I know it's customary for HN to edit titles to remove extraneous information, but removing "Linux" here really takes away something useful and relevant. This is a Linux vulnerability. If you're running *BSD or Mac or Windows, not affected.
"Why it's urgent: the bug sits in code every Linux server runs when it accepts an IPv4 TCP connection, before any application sees the connection. Anthropic, whose researcher reported it, says its Claude model wrote a working proof-of-concept exploit that runs commands as root on "Linux servers with a multipath TCP listener," with no credentials. Go programs open those listeners by default, per the Go Security Team. See the timeline."
I don't know of any Linux boxes running a multipath TCP listener in my care and I have quite a few. MP generally implies a router of some sort and the intersections in a Venn diagram continue to get smaller ...
This is still an issue and must be patched but I think it will be rare, very rare.
This is not rare. Every TCP connection in Go by default enables MPTCP [1]. Simply running a Go program that uses TCP without explicitly disabling this behavior will cause the running kernel to be vulnerable.
- MPTCP is not a requirement, it is a generic use-after-free.
- Exploitability over the internet is unlikely, most ISP routers drop packets with IP options fields.
- At least according to Red Hat, dropping packets with IP options yourself helps, but is not a full mitigation.
- Successful exploit requires multiple CPU cores to process packets, so systems with just a single core or packet processing pinned to a single core are not affected.
Tragically not enough people drop IP options. I did it in the early 2000s for a very large US network and was glad. There's lots of obvious reasons as they're generally an old school ddos path to knock out routers (get punted to the RE/RP exception path, a good way to bypass some loopback/routing engine acls if folks don't filter it right). Every few years some academics pop up with let's use IP options because we can stuff more bullshit in the datagram - it's always a bad idea.
And it takes around an hour to do this in lab setting locally:
> An enabling property of this race condition is that a lost race only fails the handshake without crashing the whole system, so a determined attacker can retry indefinitely until they succeed. In our proof of concept, it takes 48 minutes to leak a kernel pointer and another five minutes to reach the shell command execution
If you read commit logs of, say kernel.org and a distro kernel, and aren't concerned you are blissfully ignorant (and it is worse for the broader userland repos). It's particularly bad when they don't track a kernel.org LTS. Their kernel orgs are pretty lean and this has been the status quo for decades. CVEs of sufficient stature like this will get fixed but majority of other issues slip by unnoticed. LTS is kind of a myth, it trades ABI and API stability for a lot of other issues.
For years, Red Hat employed more kernel developers than anyone and contributed more. These days they're "only" the fourth largest contributor, after Intel, Google, and Meta, but they are still among the largest corporate contributors.
If that's a lean kernel org, I don't know what a fat one would look like.
Over the past few months I've started to install newer ubuntu kernels using the mainline PPA. However, it goes long periods of time without getting updates, so it's not really a satisfactory solution. In one case I just built the kernel myself.
LTS doesn't work if you want immediate fixes like the current environment requires.
Given the current and rapidly upcoming environment, would that not imply that those are no longer viable choices? As like a fairly urgent emergency consideration?
If they cannot demonstate being systematically able to adapt towards the required reaction time (minutes? hours?) by almost-comically many orders of magnitude (multiple weeks), and it is only going to get worse, then what other conclusion could there be?
Like they'll only organizationally adapt when it's far too late (everybody using their shit has already been pwned), and then it'll be an unpracticed emergency adaptation.
I don't think I can recall an instance where there was an issue this bad (a box being vulnerable just by virtue of being connected to the internet, or exposing nothing other than ssh) and I didn't have timely patches for it. I had to turn off my server and home automation system because of this. Really not acceptable at all and makes me want to switch everything to debian.
I’m pretty confused because apparently Anthropic is the group that followed “responsible disclosure” but apparently even though upstream was patched a couple weeks ago, still nothing on either.
Going by the proxmox forum the fix is already in the sources (proxmox released their kernel based on them a few days ago). But I could not see, if it is already released for the users.
Yes, we (Proxmox) included the fix for this in 7.0.14-25, which was initially packaged two weeks ago.
It went through internal QA and to the test soon after that, then a few days later to the no-subscription repository and as of yesterday morning CET it was cleared for the enterprise one, so it's available on all repos of all Products we got in their current supported releases.
For kernel updates we where even more conservative in the past, but with the current churn on often quite relevant fixes picked up the pace a bit on moving them along, trying still to balance rolling out fixes fast(er) while not doing that so fast that tricky (hardware/setup specific) regressions don't get caught.
edit: As this makes the rounds we also released a PSA for it now [0] to make our status here easier to find.
Interestingly, Ubuntu Priority is set to "High" and not "Critical" which is defined as:
"A significant problem, typically exploitable for nearly all users in a default installation of Ubuntu. Includes serious remote denial of service, local root privilege escalations, local data theft, and data loss."
The listed kernels are in the "proposed" component (and not yet in "security" or "udpates") if you want to pull them down onto canary systems for testing before going to production.
I've been compiling a list of cybersecurity RSS feeds to build a small automation (with oversight from Hermes agent) to ping me (ntfy.sh or just Telegram) when a CVE requires my intervention (matching them to a list of services I run for clients and myself.)
My list (of feeds) is still small, but this CVE did not show up, do any of you have any tips for RSS feeds to use for this purpose?
At least if you’re on Amazon Web Services behind a load balancer you probably aren’t really that impacted enough to spend Halloween patching.
> AWS Web Application Firewall, Application Load Balancer, Classic Load Balancer, TLS Listeners on Network Load Balancer, Cloud Front, API Gateway
> Customers using the above services do not receive TCP connections from untrusted sources directly when following best practices. AWS is applying updates to the underlying infrastructure of these services and no immediate customer action is required if you are using these services. We still recommend customers update their self-managed instances behind these services within the next 30 days.
I blocked packets arriving externally on my firewall with ip-options a couple of days ago. Firewall rule has zero hits, and I've got a very open ISP (andrews+arnold), if I want I can host SMTP, DNS, whatever
My FreeBSD loadbalancers block packets with IP Options with default config. It’s not rocket science, no matter how Cloud providers are trying to tell us.
It's okay guys, the authors simply don't know how to write good C. A real C programmer would not have shipped such a basic use-after-free bug. Rust is just a crutch.
Counterpoint, more than memory bugs exist, and everything's written in C. You're welcome to rewrite in Rust but you'll create countless bugs that aren't memory bugs that mostly already got fixed in the C version. I can't help but think things like fil-C are the most pragmatic route, despite performance costs, for most people relying on programs written in C.
This is a dumb argument imo. Critical vulnerabilities are mostly due to memory bugs (and not for a lack of other kinds of bugs). Most people relying on programs written in C (or even C++) should consider plans for migrating to software created with toolchains from this century. You cannot indefinitely carry on this tech debt.
Yes, you'd introduce a lot of new bugs because the code is newly written[1], but eventually you'll get to the same maturity as today except you can't have all these devastating memory-handling-related vulnerabilities
The question is whether your software will be in use long enough to be worth the cost of change more than whether it's a good idea in the long run. For Linux, I'd argue that that's likely. At least new code would ideally be contributed in a safe language, where practically possible (there'll surely be places where you need to deal with memory as a kernel)
Relevant article: reducing memory vulnerabilities through a combination of memory-safe languages and an exponential decrease of bugs as existing code ages https://security.googleblog.com/2024/09/eliminating-memory-s..., from which I'll also quote my reference for [1]: "A large-scale study of vulnerability lifetimes published in 2022 in Usenix Security [...] found that the vast majority of vulnerabilities reside in new or recently modified code"
Was going to say that, depending on the device's age, this law may apply, where article 13 sub 9 specifies a decade of updates is the minimum: https://eur-lex.europa.eu/eli/reg/2024/2847/oj
But then it turns out that this "applies from" late 2027 :/
Simultaneously Wikipedia says the Act has "entered into force" in 2024. Does anyone know the difference between "enters into force" and "applies"? Is it like this 2016–2018 grace period for GDPR where it was "law" but not enforced? (The wording sounds backwards if it's that, but I'm not a native speaker)
The good news is, if you emergency patched your Debian for php2shell, you probably got the new kernel on the same apt run. This time the embargo actually held, and the new kernel was out before the CVE came public
> Anthropic says Claude wrote the exploit "after initial prompting," that it runs "arbitrary commands as root, without any credentials or user interaction" on servers with a multipath TCP listener, and that in its proof of concept "it takes 48 minutes to leak a kernel pointer and another five minutes to reach the shell command execution."
This is wild. I'm a firmware nerd, not a backend nerd, what percentage of TCP/IP servers are 'multipath'?
Also, since IPv6 isn't affected, wouldn't it be funny if this is what it took to get everyone to switch.
My understanding is that an app explicitly needs to open a "multipath" socket. Go 1.24 does that by default, so does Caddy, these would be the big ones.
Can anyone explain how use after free results in a practical exploit?
I ask because I’ve been dabbling in rooting various closed devices at home. I’m finding AI fantastic at finding vulnerabilities statically (from firmware upgrade binaries), but when you then ask it to use it to get root or code execution it just goes in circles.
In the end it usually ends up there’s no exploit it can find, because it can’t actually influence the affected memory in a useful way. This is especially so if that memory is in the heap. On the stack it’s a lot more predictable (especially with OOB writes).
You need to do some https://en.wikipedia.org/wiki/Heap_feng_shui. If you can reasonably reliably trigger some other operation that allocated the freed memory for another purpose, you have something like a type confusion vulnerability.
One example is that you might be able to read what was written there. Here that may mean you could read another process’s packet(s). Imagine they were sending unencrypted passwords, perhaps because it’s in a trusted LAN connection.
If it’s freed it can be reallocated, so then you have pointers to the same area of memory used for completely different data structures, and this can go very wrong
I get the principle - what I struggle to find is concrete examples of how it can practically be used.
How do you know which pointer (as I say, especially if it’s in the heap)? And I know it can go wrong - but how do you do more than just crash the kernel?
In OOB writes in a stack variable it’s completely clear to me. For other situations I’d love to find real and clearly explained exploits of past UAF or OOB vulnerabilities.
It goes around in circles because a UAF alone isn't enough in a lot of cases, sometimes you also need a chain (an info leak, read/write primitive etc), a way to defeat ASLR and so on depending on what you are working on and target mitigations. Not all UAFs can be used for RCEs, some can be used only for DoS or for nothing really.
been doing exactly this lately with camera firmware and yeah the circles thing is real, but im pretty sure its a feedback loop problem, not a model problem
the model spins because it cant test its own guesses. what fixed it for me was emulating the actual device. qemu with the vendor rootfs, real binaries running, and then every claim becomes checkable: did the daemon actually parse my input, which uid is it under, what does its own log say. once it can check things it stops guessing, getting qemu to actually boot the thing was its own little hell though, took more tries than i want to admit.
the other thing i learned the hard way: most static findings die on reachability, not on exploit primitives. so i run them in the emulator first and kill the unreachable ones cheap, before spending any time on heap work
on heap vs stack, i think that intuition is desktop shaped. device userland usually has weak or no mitigations, heap uafs are way more tractable there than youd expect
Good ideas on the QEMU. I guess you’d have to patch the binary if it’s expecting particular hardware etc?
Not sure what you mean by “desktop shaped”?
Can you give a concrete example of UAF on heap? I’m learning a bit on how this is done, and eventually recognised the LLM is doing something called heap spray. But that seemed to rely on hoping some object you wrote just happened to get interpreted by some process. And that was the “no, wait, pointer f isn’t y” loops.
>the kernel handed those saved options from the request socket to the new connection without copying them, then freed them immediately when the connection went away, while another CPU could still be reading them to build a handshake reply.
If this requires a multi-core system to exploit, it's good news for most of the consumer routers that will never get updates. Saved by cheap single-core hardware.
You would be surprised. A lot of cheap consumer routers are have two or four ARM cores. The bigger issue is that they are typically running a kernel from the stone age (< 6.0.0). Sometimes a still-supported LTS kernel like 5.10 or 5.15, but then they stopped at an old patch level.
Heck, apparently even the new Unifi UCG Fiber is running 5.4.213 (September 2022), but maybe they backport some fixes?
I’m in the market for a new router. Got a unifi u7 pro for wifi already, what are the options for routers? Sounds like the only safe thing is to roll your own so you can update things on time.
My home firewall runs Ubuntu. It doesn't accept (new) incoming packets from the internet. I don't have any IoT devices except printers, whose packets the firewall rejects, and has done since I bought them. Do I need to do anything apart from wait for the patch to become available?
OpenWrt doesn't open ports by default so I think the impact is minimal, unless this can breach nftables as well. CGNAT also mitigates this as a side effect.
If you have services open on the IPv4 net however, close them immediately as a precaution.
A listener is a piece of software that advertises itself as available to inbound connections. You can do this on a variety of protocols.
Multipath TCP is a neat trick that allows a single TCP connection (TCP = Transport Control Protocol, a stateless protocol for long running connections) to use multiple physical interfaces. You could do something similar before MTCP using bonding, but this was annoying to set up and usually required application level code to efficiently use the bonded connection. MTCP makes this much simpler from an application level point of view and it can use widely diverse underlying transport layers at the same time (for instance, WiFi, Cellular and wired connections).
TCP is in the transport layer! The layers which you name are lower, such as Layer 2 (Data Link)!
MTCP, being in the transport layer, is working at a higher level of abstraction than bonding or link aggregation. There is no need for application-layer support, but it is possible, and easier, with MTCP than with the Layer 2 solutions, because MTCP is in the transport layer. That is why Go was able to activate it, and the POC uses it, because MTCP controls can be exposed at that level.
It's an extension to TCP that, similar to QUIC, allows you to use multiple address/port pairs to transmit data over a single logical stream. Both client/initiator and server/listener have to opt into the extension. This might need to be enabled explicitly by the application[1], which Go apparently does for you, or judging from other posts may be enabled by default systemwide, depending on your platform.
AFAIU, a major user of MPTCP is Apple and the iPhone, and the ubiquity of iPhone clients motivated implementation in and deployment on Linux servers.
I had to look it up too since I hadn't heard of it. It's an extension to TCP that allows responses across different NICs. Sort of like Link Aggregation on to a switch, except it can go out dissimilar interfaces, like your wifi connection and your hardwired connection. Looks like you have to opt into it when you set up your socket: https://docs.kernel.org/networking/mptcp.html
In addition to aggregating, it can also be useful in cases where one link is much slower or higher latency. For example, if you're sitting in your driveway trying to get directions in maps while your phone is still on your very weak wifi network, it's a better user experience to have it to attempt the request using both radios concurrently so that it can fallback to cellular without waiting for a timeout/connection error if you're too far for wifi to actually work well.
2027 is going to be the year of two to three major CVEs per day.
The discourse on this is weird, sounds at times as if these are “because of AI.” These are mostly pre-existing bugs, some very old, and they’ve been lurking. If they all get found we exit the other side more secure and reliable.
I went on a security kick early this year, locking down everything as much as I could. Build your systems with the assumption that you WILL get hacked. Limit blast radius. Be prepared.
The next few years will be crazy, but you're right, we'll come out the other side more secure than ever before. Just gotta make it that far!
Will be interesting to see, if AI will cause an increased demand for sysadmins. Not sure companies will go "Make no mistakes" on their (production) infrastructure.
There are microkernel operating systems out there that run the network stack in isolated, unprivileged contexts. Some of them are even not written in C.
The most terrifying part of this is all the devices that might be affected. Ignore servers and desktops. Linux 4.4 came out nearly 11 years ago. While most Linux devices' firmware is actually more ancient than that (Linux 2.x and 3.x isn't uncommon), any device that did ship with Linux 4.4+ is going to get hacked, because nobody patches those devices. Any smart device in the world that isn't a server, desktop, or microcontroller, is probably running Linux.
As part of the Software Building Code (that we don't have, and desperately need), one of the things we should have is mitigation for these abandoned internet safety risks. Here's how I would define that section:
Section 4 Connections to Public Internet
Section 4.1 Device Support
Devices connected to the public internet WILL require one of the following:
a) Guaranteed LTS support for a minimum of 10 years
b) Guaranteed rolling release support for a minimum of 10 years
Devices without this support are not permitted to be connected to the public internet.
Section 4.2 Vendor Responsibility
When releasing devices, vendors must determine whether this device is certified for
public internet use. Support must be maintained according to S4.1. Failure to comply will
result in fines of up to $5,000 per affected device.
Section 4.3 Installer Responsibility
Any device connected to the public internet which is not certified for public internet
use is in violation, and will be subject to fines of up to $500 per affected device.
Section 4.4 Device Owner Responsibility
Any installed devices will be replaced once they reach their End Of Life period,
or after 10 years, whichever comes first. Installed devices in use that exceed this
period are in violation, and subject to fines of up to $250 per affected device.
(These fines are tiny compared to the fines for things like fire code violations, but enough money that a company, contractor, or individual would rather fix their device than pay the fines)
It works mostly fine, pretty easy to work with, might perform well when you're sleeping / not around, packages are old (not neccesarily a bad thing). The default kernel is vintage 5.15, so just compile your own. Also elilo really sucks so bring your own bootloader while you're at it.
I tried to find a mitigation using a ufw filter that rejects IPv4 packets with too large headers but it didn't work. It broke something essential and I had to switch it off again. I'd be interested in hearing about a temporary mitigation using firewall rules.
Add the below rule onto your machine's /etc/ufw/before.rules to mitigate it.
# CVE-2026-98432 mitigation: drop TCP packets carrying IPv4 extended options
-A ufw-before-input -p tcp -m u32 --u32 "0>>24&0xF=6:15" -j DROP
Any value >5 in this field means ip extended header options and so values of 6 through 15 should be dropped.
Note that I don't just drop syn packets like the mptcp exploit because any tcp packet could do it in theory.
This works for me on multiple servers and home desktops and my hardware linux firewall/router. I did it a couple days ago when this was first announced. The iptables counter for matches haven't gone up at all on my VPS servers that gets lots of traffic. The counter only goes up when I manually trigger it to test. Everything continues to work nominally with these in place.
It might be bit of an effort to get Fil-C compiling the Linux kernel. As I understand it, it would amount to running garbage collector in the kernel, so some care would probably need to be taken to ensure it doesn't stop things at the wrong time, e.g. interrupts.
It's kinda a really bad time to be a C-loving, AI-hating, fanboi.
Do we at least entertain the idea that some rewrites of some things in safer languages could be a desirable goal? (not saying it's practical or not: just asking if C lovers are willing to reflect a bit on what's going on atm).
Finally a usecase for mptcp on linux. Been waiting and trying off and on for years to get it to do something, but now it can give a nice remote root shell. Well, not to me, I just get to patch devices.
Right. The "Affected Products" section on https://nvd.nist.gov is absolutely useless and highly misleading. I don't understand how this can be the case for something so security critical.
> TCP Use-After-Free: CVE-2026-98432 / CVSS 9.8
I know it's customary for HN to edit titles to remove extraneous information, but removing "Linux" here really takes away something useful and relevant. This is a Linux vulnerability. If you're running *BSD or Mac or Windows, not affected.
Quite, however it looks quite rare:
"Why it's urgent: the bug sits in code every Linux server runs when it accepts an IPv4 TCP connection, before any application sees the connection. Anthropic, whose researcher reported it, says its Claude model wrote a working proof-of-concept exploit that runs commands as root on "Linux servers with a multipath TCP listener," with no credentials. Go programs open those listeners by default, per the Go Security Team. See the timeline."
I don't know of any Linux boxes running a multipath TCP listener in my care and I have quite a few. MP generally implies a router of some sort and the intersections in a Venn diagram continue to get smaller ...
This is still an issue and must be patched but I think it will be rare, very rare.
This is not rare. Every TCP connection in Go by default enables MPTCP [1]. Simply running a Go program that uses TCP without explicitly disabling this behavior will cause the running kernel to be vulnerable.
1: https://groups.google.com/g/golang-announce/c/PCoQcdxoScw
"TCP stack" versus "Linux TCP stack" is an OOM in terms of relevance.
Out of memory?! That's terrible!
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Some notes I've got about this:
- MPTCP is not a requirement, it is a generic use-after-free.
- Exploitability over the internet is unlikely, most ISP routers drop packets with IP options fields.
- At least according to Red Hat, dropping packets with IP options yourself helps, but is not a full mitigation.
- Successful exploit requires multiple CPU cores to process packets, so systems with just a single core or packet processing pinned to a single core are not affected.
Tragically not enough people drop IP options. I did it in the early 2000s for a very large US network and was glad. There's lots of obvious reasons as they're generally an old school ddos path to knock out routers (get punted to the RE/RP exception path, a good way to bypass some loopback/routing engine acls if folks don't filter it right). Every few years some academics pop up with let's use IP options because we can stuff more bullshit in the datagram - it's always a bad idea.
> Exploitability over the internet is unlikely, most ISP routers drop packets with ipoptions fields.
That doesn't track. Apple iPhones are a major user of MPTCP and they report the majority of requests supporting MPTCP, IIRC 70+%.
MPTCP uses TCP options fields, the vulnerability is in IP options.
Dropping packets with IP options from XDP should be a more complete mitigation (also more performant).
https://en.wikipedia.org/wiki/Express_Data_Path for anyone else wondering what that is
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I'm wondering if Android is vulnerable, since it is based on Linux?
And it takes around an hour to do this in lab setting locally:
> An enabling property of this race condition is that a lost race only fails the handshake without crashing the whole system, so a determined attacker can retry indefinitely until they succeed. In our proof of concept, it takes 48 minutes to leak a kernel pointer and another five minutes to reach the shell command execution
source: https://www.anthropic.com/research/discovering-vulnerabiliti...
How are Ubuntu and RHEL not fixed? Few operating systems market themselves more as suitable for servers. What are they doing over there?
If you read commit logs of, say kernel.org and a distro kernel, and aren't concerned you are blissfully ignorant (and it is worse for the broader userland repos). It's particularly bad when they don't track a kernel.org LTS. Their kernel orgs are pretty lean and this has been the status quo for decades. CVEs of sufficient stature like this will get fixed but majority of other issues slip by unnoticed. LTS is kind of a myth, it trades ABI and API stability for a lot of other issues.
"Their kernel orgs are pretty lean"
For years, Red Hat employed more kernel developers than anyone and contributed more. These days they're "only" the fourth largest contributor, after Intel, Google, and Meta, but they are still among the largest corporate contributors.
If that's a lean kernel org, I don't know what a fat one would look like.
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Over the past few months I've started to install newer ubuntu kernels using the mainline PPA. However, it goes long periods of time without getting updates, so it's not really a satisfactory solution. In one case I just built the kernel myself.
LTS doesn't work if you want immediate fixes like the current environment requires.
Unfortunately, as a ZFS on Linux user, LTS is the best way to get continual updates without breaking my system.
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Given the current and rapidly upcoming environment, would that not imply that those are no longer viable choices? As like a fairly urgent emergency consideration?
If they cannot demonstate being systematically able to adapt towards the required reaction time (minutes? hours?) by almost-comically many orders of magnitude (multiple weeks), and it is only going to get worse, then what other conclusion could there be?
Like they'll only organizationally adapt when it's far too late (everybody using their shit has already been pwned), and then it'll be an unpracticed emergency adaptation.
I don't think I can recall an instance where there was an issue this bad (a box being vulnerable just by virtue of being connected to the internet, or exposing nothing other than ssh) and I didn't have timely patches for it. I had to turn off my server and home automation system because of this. Really not acceptable at all and makes me want to switch everything to debian.
I’m pretty confused because apparently Anthropic is the group that followed “responsible disclosure” but apparently even though upstream was patched a couple weeks ago, still nothing on either.
> How are Ubuntu and RHEL not fixed?
Ubuntu has had kernels in the "proposed" component for several days now if you want to pull it in manually. Not yet pushed to "security" or "updates".
Is there an RTFM for 'pull it manually'?
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It seems particularly crazy for Ubuntu given that Debian released their fix something like a couple weeks ago.
It's one of two things: Either they have found some regression with enterprise customers, or they are not happy with the fix.
RHEL runs with MP-TCP disabled by default, they initially listed it as Important only to later raise it to Critical.
Going by the proxmox forum the fix is already in the sources (proxmox released their kernel based on them a few days ago). But I could not see, if it is already released for the users.
https://forum.proxmox.com/threads/cve-2026-98432-in-proxmox-...
Yes, we (Proxmox) included the fix for this in 7.0.14-25, which was initially packaged two weeks ago.
It went through internal QA and to the test soon after that, then a few days later to the no-subscription repository and as of yesterday morning CET it was cleared for the enterprise one, so it's available on all repos of all Products we got in their current supported releases.
For kernel updates we where even more conservative in the past, but with the current churn on often quite relevant fixes picked up the pace a bit on moving them along, trying still to balance rolling out fixes fast(er) while not doing that so fast that tricky (hardware/setup specific) regressions don't get caught.
edit: As this makes the rounds we also released a PSA for it now [0] to make our status here easier to find.
[0]: https://forum.proxmox.com/threads/proxmox-virtual-environmen...
Running regression tests I assume; they can't just YOLO shit like most OSS projects for the exact reason you mention.
It could be that it is more YOLO not patching this ASAP. Maybe better to risk some regressions.
For a month?
>How are Ubuntu and RHEL not fixed?
IMNSHO this makes them unfit for purpose. I think this is the nail in the coffin for Ubuntu for me.
It's not a good look.
I pulled in from -proposed this time.
Ubuntu was slow on the brotli / CVE-2026-111497 updates as well.
What would you suggest for enterprise use of Linux if RHEL is no longer fit for purpose?
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No patches for Ubuntu or red hat yet.
https://ubuntu.com/security/CVE-2026-98432
https://access.redhat.com/security/cve/cve-2026-98432
Interestingly, Ubuntu Priority is set to "High" and not "Critical" which is defined as:
"A significant problem, typically exploitable for nearly all users in a default installation of Ubuntu. Includes serious remote denial of service, local root privilege escalations, local data theft, and data loss."
Makes you wonder what the critical level is for
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> https://ubuntu.com/security/CVE-2026-98432
The listed kernels are in the "proposed" component (and not yet in "security" or "udpates") if you want to pull them down onto canary systems for testing before going to production.
so just block multipath and add the firewall rule from article that drops packets with IPv4 options
"the bug sits in code every Linux server runs when it accepts an IPv4 TCP connection, before any application sees the connection."
Is iptables considered an "application" here? I.e. can this bug be triggered before iptables drops the packet?
Both of which we are finding out are apparently insufficient to mitigate this.
Hoping fix will be out soon so we don’t have to.
I've been compiling a list of cybersecurity RSS feeds to build a small automation (with oversight from Hermes agent) to ping me (ntfy.sh or just Telegram) when a CVE requires my intervention (matching them to a list of services I run for clients and myself.)
My list (of feeds) is still small, but this CVE did not show up, do any of you have any tips for RSS feeds to use for this purpose?
https://pwn.watch/ has an RSS feed available
That heat map this month
Any chance you’d mind sharing your list?
The openwall oss-security list usually covers a decent number of issues and this CVE was mentioned there yesterday:
https://www.openwall.com/lists/oss-security/
At least if you’re on Amazon Web Services behind a load balancer you probably aren’t really that impacted enough to spend Halloween patching.
> AWS Web Application Firewall, Application Load Balancer, Classic Load Balancer, TLS Listeners on Network Load Balancer, Cloud Front, API Gateway
> Customers using the above services do not receive TCP connections from untrusted sources directly when following best practices. AWS is applying updates to the underlying infrastructure of these services and no immediate customer action is required if you are using these services. We still recommend customers update their self-managed instances behind these services within the next 30 days.
[0]: https://aws.amazon.com/security/security-bulletins/2026-160-...
I'm more worried about my consumer-grade router.
I blocked packets arriving externally on my firewall with ip-options a couple of days ago. Firewall rule has zero hits, and I've got a very open ISP (andrews+arnold), if I want I can host SMTP, DNS, whatever
The timeline says the CVE was reported over 2 weeks ago, so why are the alarms sounding now?
Note: AWS NLB doesn't terminate TCP for TCP listeners.
It would be great if they introduced mitigations for this vulnerability though.
Another reason hyperscaler cloud providers will continue to grow (IMO)!
My FreeBSD loadbalancers block packets with IP Options with default config. It’s not rocket science, no matter how Cloud providers are trying to tell us.
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My VPS was auto-updated and restarted more than 14 days ago. The logs have rolled already. Probably October 12 early morning.
Another reason NixOS will continue to grow :)
Unless they themselves (underlying services) get hacked...
It's okay guys, the authors simply don't know how to write good C. A real C programmer would not have shipped such a basic use-after-free bug. Rust is just a crutch.
Counterpoint, more than memory bugs exist, and everything's written in C. You're welcome to rewrite in Rust but you'll create countless bugs that aren't memory bugs that mostly already got fixed in the C version. I can't help but think things like fil-C are the most pragmatic route, despite performance costs, for most people relying on programs written in C.
This is a dumb argument imo. Critical vulnerabilities are mostly due to memory bugs (and not for a lack of other kinds of bugs). Most people relying on programs written in C (or even C++) should consider plans for migrating to software created with toolchains from this century. You cannot indefinitely carry on this tech debt.
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Yes, you'd introduce a lot of new bugs because the code is newly written[1], but eventually you'll get to the same maturity as today except you can't have all these devastating memory-handling-related vulnerabilities
The question is whether your software will be in use long enough to be worth the cost of change more than whether it's a good idea in the long run. For Linux, I'd argue that that's likely. At least new code would ideally be contributed in a safe language, where practically possible (there'll surely be places where you need to deal with memory as a kernel)
Relevant article: reducing memory vulnerabilities through a combination of memory-safe languages and an exponential decrease of bugs as existing code ages https://security.googleblog.com/2024/09/eliminating-memory-s..., from which I'll also quote my reference for [1]: "A large-scale study of vulnerability lifetimes published in 2022 in Usenix Security [...] found that the vast majority of vulnerabilities reside in new or recently modified code"
With all the "Claude rewrote X in rust!" posts lately, I'm waiting on the inevitable Linux kernel rewrite post.
Vibe code aside I feel targeted rewrites are becoming more and more justified.
I wouldn’t be surprised if we start seeing individual drivers and subsystems move over.
The Linux maintainers have been extremely conservative with the Rust introduction but after the endless CVE apocalypse they might be more receptive.
Everything talks about this in terms of servers, but what about desktop Linux in typical setups? Consumer modems and routers? IoT junk?
IoT devices will get fixes delivered on the 12th of never.
Was going to say that, depending on the device's age, this law may apply, where article 13 sub 9 specifies a decade of updates is the minimum: https://eur-lex.europa.eu/eli/reg/2024/2847/oj But then it turns out that this "applies from" late 2027 :/
Simultaneously Wikipedia says the Act has "entered into force" in 2024. Does anyone know the difference between "enters into force" and "applies"? Is it like this 2016–2018 grace period for GDPR where it was "law" but not enforced? (The wording sounds backwards if it's that, but I'm not a native speaker)
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But are they exploitably vulnerable to this specifically in typical setups?
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The security fixed will be installed next tuesday.
You should assume your IoT junk is already compromised, that's why your IoT junk runs on a dedicated VLAN.
What kernel is the router managing these VLANs running?
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Desktop Linux in typical setups? Consumer modems and routers?
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I suppose I'm not the only one feeling worn out by this tidal wave of vulnerabilities that I somehow have to keep up to?
The good news is, if you emergency patched your Debian for php2shell, you probably got the new kernel on the same apt run. This time the embargo actually held, and the new kernel was out before the CVE came public
The only way to survive is to just update everything daily or faster.
At work we currently have a weekly release schedule but im going to push to speed it up because 1 week is far too long to leave packages out of date.
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Nope. This was just the start.
Fixed upstream in:[1]
7.3 (2026-10-18)
7.2.10 (2026-10-11)
6.18.56 (2026-10-11)
6.12.113 (2026-10-15)
6.6.159 (2026-10-15)
6.1.190 (2026-10-15)
5.15.225 (2026-10-15)
[1] https://lore.kernel.org/all/?q=tcp_v4_reqsk_destructor -- check for "kfree_rcu" being used instead of "kfree" within "tcp_v4_reqsk_destructor" (net/ipv4/tcp_ipv4.c)
> Anthropic says Claude wrote the exploit "after initial prompting," that it runs "arbitrary commands as root, without any credentials or user interaction" on servers with a multipath TCP listener, and that in its proof of concept "it takes 48 minutes to leak a kernel pointer and another five minutes to reach the shell command execution."
This is wild. I'm a firmware nerd, not a backend nerd, what percentage of TCP/IP servers are 'multipath'?
Also, since IPv6 isn't affected, wouldn't it be funny if this is what it took to get everyone to switch.
> what percentage of TCP/IP servers are 'multipath'?
no idea, but at least Tailscale and Caddy were opening MPTCP sockets on servers I checked.
My understanding is that an app explicitly needs to open a "multipath" socket. Go 1.24 does that by default, so does Caddy, these would be the big ones.
Your understanding seems to be wrong.
Every Ubuntu version in the last decade is currently vulnerable.
https://ubuntu.com/security/CVE-2026-98432
Patches not yet available. That makes this a big deal.
This article says that this isn’t app level but is level and can be exploited before requests reach apps.
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Can anyone explain how use after free results in a practical exploit?
I ask because I’ve been dabbling in rooting various closed devices at home. I’m finding AI fantastic at finding vulnerabilities statically (from firmware upgrade binaries), but when you then ask it to use it to get root or code execution it just goes in circles.
In the end it usually ends up there’s no exploit it can find, because it can’t actually influence the affected memory in a useful way. This is especially so if that memory is in the heap. On the stack it’s a lot more predictable (especially with OOB writes).
You need to do some https://en.wikipedia.org/wiki/Heap_feng_shui. If you can reasonably reliably trigger some other operation that allocated the freed memory for another purpose, you have something like a type confusion vulnerability.
One example is that you might be able to read what was written there. Here that may mean you could read another process’s packet(s). Imagine they were sending unencrypted passwords, perhaps because it’s in a trusted LAN connection.
If it’s freed it can be reallocated, so then you have pointers to the same area of memory used for completely different data structures, and this can go very wrong
I get the principle - what I struggle to find is concrete examples of how it can practically be used.
How do you know which pointer (as I say, especially if it’s in the heap)? And I know it can go wrong - but how do you do more than just crash the kernel?
In OOB writes in a stack variable it’s completely clear to me. For other situations I’d love to find real and clearly explained exploits of past UAF or OOB vulnerabilities.
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It goes around in circles because a UAF alone isn't enough in a lot of cases, sometimes you also need a chain (an info leak, read/write primitive etc), a way to defeat ASLR and so on depending on what you are working on and target mitigations. Not all UAFs can be used for RCEs, some can be used only for DoS or for nothing really.
been doing exactly this lately with camera firmware and yeah the circles thing is real, but im pretty sure its a feedback loop problem, not a model problem
the model spins because it cant test its own guesses. what fixed it for me was emulating the actual device. qemu with the vendor rootfs, real binaries running, and then every claim becomes checkable: did the daemon actually parse my input, which uid is it under, what does its own log say. once it can check things it stops guessing, getting qemu to actually boot the thing was its own little hell though, took more tries than i want to admit.
the other thing i learned the hard way: most static findings die on reachability, not on exploit primitives. so i run them in the emulator first and kill the unreachable ones cheap, before spending any time on heap work
on heap vs stack, i think that intuition is desktop shaped. device userland usually has weak or no mitigations, heap uafs are way more tractable there than youd expect
If you really learned anything you should post your own thoughts, not whatever this lowercased Claudish is.
Oh yes definitely seen the reachability problem!
Good ideas on the QEMU. I guess you’d have to patch the binary if it’s expecting particular hardware etc?
Not sure what you mean by “desktop shaped”?
Can you give a concrete example of UAF on heap? I’m learning a bit on how this is done, and eventually recognised the LLM is doing something called heap spray. But that seemed to rely on hoping some object you wrote just happened to get interpreted by some process. And that was the “no, wait, pointer f isn’t y” loops.
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>the kernel handed those saved options from the request socket to the new connection without copying them, then freed them immediately when the connection went away, while another CPU could still be reading them to build a handshake reply.
If this requires a multi-core system to exploit, it's good news for most of the consumer routers that will never get updates. Saved by cheap single-core hardware.
You would be surprised. A lot of cheap consumer routers are have two or four ARM cores. The bigger issue is that they are typically running a kernel from the stone age (< 6.0.0). Sometimes a still-supported LTS kernel like 5.10 or 5.15, but then they stopped at an old patch level.
Heck, apparently even the new Unifi UCG Fiber is running 5.4.213 (September 2022), but maybe they backport some fixes?
[1] https://community.ui.com/releases/dd0283dc-bf71-4140-ae1d-c1...
Note that even the latest OpenWRT is vulnerable to this, I'm running OpenWRT 25.12.6 and the kernel version is 6.12.112
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I’m in the market for a new router. Got a unifi u7 pro for wifi already, what are the options for routers? Sounds like the only safe thing is to roll your own so you can update things on time.
Those routers probably have 20 other critical un-patched exploits ...
An entire ecosystem of malware crawling and cohabiting in them.
god this page could hardly be more ai generated if it tried
actual link: https://nvd.nist.gov/vuln/detail/cve-2026-98432
My home firewall runs Ubuntu. It doesn't accept (new) incoming packets from the internet. I don't have any IoT devices except printers, whose packets the firewall rejects, and has done since I bought them. Do I need to do anything apart from wait for the patch to become available?
How does your internet work, if the firewall doesn't accept incoming packets?
Is OpenWRT affected? Because that would be a real fawkin problem.
OpenWrt doesn't open ports by default so I think the impact is minimal, unless this can breach nftables as well. CGNAT also mitigates this as a side effect.
If you have services open on the IPv4 net however, close them immediately as a precaution.
How do you plan on reopening them again after you've closed 443 and 22?
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As much as I hate to link to this site, this particular sub is very good:
https://www.reddit.com/r/openwrt/comments/1xka85h/is_the_ope...
They say 25.12-SNAPSHOT has it fixed
I was sorely tempted to fully bypass the kernel for networking before, and this isn't exactly giving me warm fuzzies for staying.
Without a test-case, read POC, how do I verify if my server is affected?
What is a "multipath TCP listener"?
A listener is a piece of software that advertises itself as available to inbound connections. You can do this on a variety of protocols.
Multipath TCP is a neat trick that allows a single TCP connection (TCP = Transport Control Protocol, a stateless protocol for long running connections) to use multiple physical interfaces. You could do something similar before MTCP using bonding, but this was annoying to set up and usually required application level code to efficiently use the bonded connection. MTCP makes this much simpler from an application level point of view and it can use widely diverse underlying transport layers at the same time (for instance, WiFi, Cellular and wired connections).
> Transport Control Protocol, a stateless protocol
TCP is stateful by definition, and that is why it supports robust error correction and reliable streams of data. UDP is its stateless counterpart.
> bonding, ... usually required application level code
No, it doesn't. https://en.wikipedia.org/wiki/Link_aggregation
> underlying transport layers
TCP is in the transport layer! The layers which you name are lower, such as Layer 2 (Data Link)!
MTCP, being in the transport layer, is working at a higher level of abstraction than bonding or link aggregation. There is no need for application-layer support, but it is possible, and easier, with MTCP than with the Layer 2 solutions, because MTCP is in the transport layer. That is why Go was able to activate it, and the POC uses it, because MTCP controls can be exposed at that level.
See https://en.wikipedia.org/wiki/Multipath_TCP
It's an extension to TCP that, similar to QUIC, allows you to use multiple address/port pairs to transmit data over a single logical stream. Both client/initiator and server/listener have to opt into the extension. This might need to be enabled explicitly by the application[1], which Go apparently does for you, or judging from other posts may be enabled by default systemwide, depending on your platform.
AFAIU, a major user of MPTCP is Apple and the iPhone, and the ubiquity of iPhone clients motivated implementation in and deployment on Linux servers.
[1] https://docs.kernel.org/networking/mptcp.html#sockets-api
I had to look it up too since I hadn't heard of it. It's an extension to TCP that allows responses across different NICs. Sort of like Link Aggregation on to a switch, except it can go out dissimilar interfaces, like your wifi connection and your hardwired connection. Looks like you have to opt into it when you set up your socket: https://docs.kernel.org/networking/mptcp.html
You have a Wifi network interface and a wired Ethernet one, multipath is somehow combining the two together.
In addition to aggregating, it can also be useful in cases where one link is much slower or higher latency. For example, if you're sitting in your driveway trying to get directions in maps while your phone is still on your very weak wifi network, it's a better user experience to have it to attempt the request using both radios concurrently so that it can fallback to cellular without waiting for a timeout/connection error if you're too far for wifi to actually work well.
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Some previous discussion: https://news.ycombinator.com/item?id=50299182
The linked source spun up my fans with 100% GPU utilization. Is there some... unwelcome... script running?
What does this enable an attacker to do exactly? RCE? DoS? Unknown?
If you run a custom kernel chances are you're not affected:
# CONFIG_MPTCP is not set
Yup, was nice to see on my gentoo system. And then this amusing tweet from the grsecurity guy: https://x.com/spendergrsec/status/2116602388471758887
2027 is going to be the year of two to three major CVEs per day.
The discourse on this is weird, sounds at times as if these are “because of AI.” These are mostly pre-existing bugs, some very old, and they’ve been lurking. If they all get found we exit the other side more secure and reliable.
I went on a security kick early this year, locking down everything as much as I could. Build your systems with the assumption that you WILL get hacked. Limit blast radius. Be prepared.
The next few years will be crazy, but you're right, we'll come out the other side more secure than ever before. Just gotta make it that far!
Will be interesting to see, if AI will cause an increased demand for sysadmins. Not sure companies will go "Make no mistakes" on their (production) infrastructure.
> If they all get found we exit the other side more secure and reliable.
I agree, but as yet we have no idea how much pain we have to pass through to get to the other side.
On the other side we have a Linux networking stack written in Rust.
There are microkernel operating systems out there that run the network stack in isolated, unprivileged contexts. Some of them are even not written in C.
MikroTik routers seem affected but mitigations are available.
Watch your Linux systems for kernel updates. Reboot!
If you use sysctl to disable mptcp, you need to do that again after each reboot.
The most terrifying part of this is all the devices that might be affected. Ignore servers and desktops. Linux 4.4 came out nearly 11 years ago. While most Linux devices' firmware is actually more ancient than that (Linux 2.x and 3.x isn't uncommon), any device that did ship with Linux 4.4+ is going to get hacked, because nobody patches those devices. Any smart device in the world that isn't a server, desktop, or microcontroller, is probably running Linux.
As part of the Software Building Code (that we don't have, and desperately need), one of the things we should have is mitigation for these abandoned internet safety risks. Here's how I would define that section:
(These fines are tiny compared to the fines for things like fire code violations, but enough money that a company, contractor, or individual would rather fix their device than pay the fines)
If I am reading this right, Slackware 15.0 is already fixed:
You’re still on slackware? I’ve not thought about it in years! How’re things over there?
It works mostly fine, pretty easy to work with, might perform well when you're sleeping / not around, packages are old (not neccesarily a bad thing). The default kernel is vintage 5.15, so just compile your own. Also elilo really sucks so bring your own bootloader while you're at it.
Oh joy.
I tried to find a mitigation using a ufw filter that rejects IPv4 packets with too large headers but it didn't work. It broke something essential and I had to switch it off again. I'd be interested in hearing about a temporary mitigation using firewall rules.
Add the below rule onto your machine's /etc/ufw/before.rules to mitigate it.
Any value >5 in this field means ip extended header options and so values of 6 through 15 should be dropped. Note that I don't just drop syn packets like the mptcp exploit because any tcp packet could do it in theory.
This works for me on multiple servers and home desktops and my hardware linux firewall/router. I did it a couple days ago when this was first announced. The iptables counter for matches haven't gone up at all on my VPS servers that gets lots of traffic. The counter only goes up when I manually trigger it to test. Everything continues to work nominally with these in place.
[06:00]
How are people finding Fil-C? It's designed to avoid things like this.
It might be bit of an effort to get Fil-C compiling the Linux kernel. As I understand it, it would amount to running garbage collector in the kernel, so some care would probably need to be taken to ensure it doesn't stop things at the wrong time, e.g. interrupts.
Does it support writing kernels?
Let me guess... The bug is in C code?
(reading TFA)
Ah yup.
And moreover it's a security issue found by LLMs.
It's kinda a really bad time to be a C-loving, AI-hating, fanboi.
Do we at least entertain the idea that some rewrites of some things in safer languages could be a desirable goal? (not saying it's practical or not: just asking if C lovers are willing to reflect a bit on what's going on atm).
Get rewriting, soldier!
maybe
i’d focus on writing new stuff with rust though, not rewriting old stuff
and time will tell whether it actually reduces bugs or just change the failure modes to something else
also C will always be there in some way or the other, at least in conventions and syntax
Who wrote the bug? Very likely someone at Redhat.
Finally a usecase for mptcp on linux. Been waiting and trying off and on for years to get it to do something, but now it can give a nice remote root shell. Well, not to me, I just get to patch devices.
In an earlier report, it said only affected is kernel 4.4, not all since. This quite dramatic now.
I see. https://nvd.nist.gov/vuln/detail/cve-2026-98432 affected versions format is the culprit. Entirely unusable. We do have versions, branch names and tags for a reason.
Wrong. Every kernel from 4.4 onward is affected until the fixed releases (5.10.272, 5.15.223, 6.1.190 and so on).
Right. The "Affected Products" section on https://nvd.nist.gov is absolutely useless and highly misleading. I don't understand how this can be the case for something so security critical.