Comment by johnmaguire

4 months ago

This is exactly my point: if Apple has SPF/DKIM/DMARC configured correctly, then Zendesk should be validating the email sender. That they didn't is technically an SPF/DKIM/DMARC issue - a bug in Zendesk - but it is not a customer misconfiguration issue.

7 comments

johnmaguire

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fweimer  4 months ago

You don't want to too strict technical validations on your helpdesk contact points, though. It's supposed to be reachable when things are broken. So it's not as easy as just reconfiguring incoming mail relays. You might need separate domains for extended validation, or a reliable (!) way to relay authentication results to those mail endpoints that need it. Come to think of it, presenting email validation results to helpdesk staff might be a good idea in general.

tryauuum  4 months ago

if someone's reading this thread: yes, apple does have dmarc / spf

    $ dig id.apple.com TXT +short
    "v=spf1 include:_spf-txn.apple.com include:_spf-mkt.apple.com include:_spf.apple.com include:icloud.com ~all"
    $ dig _dmarc.id.apple.com TXT +short
    "v=DMARC1; p=reject; rua=mailto:d@rua.agari.com; ruf=mailto:d@ruf.agari.com;"

  • teddyh  4 months ago

    They also seem to have DKIM. To find out, first we need an authoritative name server for id.apple.com:

      $ dig +short id.apple.com NS
  ns1-235.akam.net.
  ns1-45.akam.net.
  asia3.akam.net.
  asia2.akam.net.
  eur5.akam.net.
  usw2.akam.net.
  usw6.akam.net.
  use1.akam.net.

    We pick an arbitrary nameserver and see if the _domainkey subdomain gives NXDOMAIN or NORERROR:

      $ dig +noall +comments +norecurse @ns1-235.akam.net _domainkey.id.apple.com TXT | grep HEADER
  ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12521

    Good, it gives NOERROR, which indicates the existence of subdomains. Just to be sure, we check some other arbitrary non-existing subdomain, to see if it gives NXDOMAIN as it should:

      $ dig +noall +comments +norecurse @ns1-235.akam.net zojglgrcqk.id.apple.com TXT | grep HEADER
  ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 5653

    Since it gives the expected NXDOMAIN, this strongly indicates that there are DNS records present on subdomains of “_domainkey.id.apple.com”; i.e. DKIM keys.

    (Of course, if you have ever recieved e-mail from an address @id.apple.com, you would see the selector name in the DKIM signature header, and could look up the corresponding DKIM record directly. The above method is for when you don’t have access to that.)

  • hmottestad  4 months ago

    And it’s still out of scope for the HackerOne bug bounty program.

    • dns_snek  4 months ago

      Future hackers, take note. If vulnerabilities you discover have any chance of being misinterpreted as "out of scope" by some bureaucrat at HackerOne, even though they're obviously applicable and dangerous, sell them on the market instead.