Comment by scoodah
19 hours ago
I really wish they would have expanded on this paragraph in their article further:
> The configuration used here had no jailer. Firecracker's production containment includes dropping privileges and restricting the process through namespaces and seccomp. A deployment using those controls requires a separate assessment of the privileges and resources available after compromising its VMM.
If I'm understanding all of this correctly, a properly jailed and configured firecracker instance would greatly reduce the blast radius of this escape, and I feel as though it would have been good for them to explain what jailing and dropping privileges would do to help. I'd hope most production firecracker deployments would be doing this already.
Not saying that this is any less severe and the root issue is not specific to Firecracker, but to a flaw in the kernel's network code -- they just used an insecure firecracker configuration to demonstrate it. However, I feel like some are taking this as a flaw with firecracker when its not. This is an issue in the kernel networking stack.
That's a good catch. Yes, since they've only proven this up to the jailer boundary, you'd need a second and relatively powerful LPE vulnerability to get real host control out of this.
Thanks to frontier reasoning agents, Linux is completely riddled in ways you can discover 900+ LPE vulnerabilities. [0]
Another wave of vulnerabilities like this are yet to be discovered in Linux. We are just seeing how weak C and C++ based OSes and kernels are when put under hundreds of AI agents.
[0] https://openai.com/index/a-thousand-fewer-paths-to-root/
Watch Hartman’s response to the first wave of issues found by AI. Super dismissive and ignorant.
I’m not sure the people that caused this will be the one fixing it.
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And how many of these vulns are in code for legacy hardware or filesystem support that in no way reflects threats against modern Linux installs? I wager the overwhelming majority of them.
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We always knew this, it has been understood since nearly the dawn of the monokernel OS that there is always a route to privilege escalation somewhere. This is why even for web applications that would be better served by a shell, people choose CGI-style interfaces instead.
The only reason it wasn't seen as a problem was due to the effort and time it took to find and exploit them.
> This is an issue in the kernel networking stack.
Exactly, its not a firecracker issue. Using firecracker without a jailer is like setting your password to "password".
Hang on, what are you getting at?
They ran it without a jailer, and exploited a bug in the linux socket code. Firecracker was just how they invoked/worked with /dev/kvm. It is not a firecracker bug. Its sensationalist nonsense.
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Nope. The exploit compromises the host kernel. The researchers built an unconventional exploit chain in which they used the host kernel compromise to compromise the host firecracker userspace code, but I see no fundamental reason they couldn't have compromised something else in the host kernel.
Wait, this is also presumably true, come to think of it. I'm a little fuzzy because they document the memory disclosure primitive carefully but not the memory writes they also got from it --- but whatever those are, they're hitting kernel memory? But the exploit they're describing here gets code execution out of Firecracker itself, not the kernel.
AIUI they’ve chosen as their target the host userspace pt_regs, i.e. the kernel structure that stores Firecracker’s register state. If they can find it and write to it, they can control the complete register state of Firecracker.
I assume they chose it as their target because Firecracker, like most Linux KVM userspace [0], maps guest memory into its own address space, giving an easy place to write gadgets.
My personal favorite thing to poke into pt_regs is an actual privileged (CPL0) context. [1] Returning from the kernel right back to a controlled kernel context is allowed by the CPU :)
[0] Until fairly recently this was mandatory. These days it’s possible to ask KVM to map something into the guest without having it in host userspace memory.
[1] Corrupt pt_regs so it executes user memory in kernel mode:
https://seclists.org/oss-sec/2015/q3/291
I think this may be my favorite of all exploits I’ve ever written. In fact, I often made a point of not writing interesting exploits for corruption bugs I found, but this one was too much fun to pass up.
Yeah, they're not saying a lot there. And then the proof of concept code is just being passed the physical addresses of the pages they talk about as command line args, and is just opening /dev/mem to do brain surgery on them.
Which like, isn't really a proof of concept of anything being described.
"That was always allowed".
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yup, the other firecracker escape recently (https://www.coinspect.com/blog/firecracker-escape/) popped the jailer via io_uring (tl;dr firecracker was filtering syscalls appropriately with seccomp, and was filtering the uring _they_ initiated, so attacker just got them to pop a new unfiltered uring, which is rather nice).
Just for what it's worth, that escape is much more situational than PwnEscape (there have been other escapes that depended on nested KVM, as well). Pretty much everyone seems to have been exposed with PwnEscape, because everyone using Firecracker is also using virtio-net.
I actually do use Firecracker without a network adapter, though vsock/virtio could have remaining issues
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