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Message-ID: <95ddd38e-2e23-4dee-b03c-a376d8cb9814@gmail.com>
Date: Tue, 29 Oct 2024 21:09:01 -0500
From: Jacob Bachmeyer <jcb62281@...il.com>
To: oss-security@...ts.openwall.com
Subject: Re: CVE-2024-36905: Linux kernel: Divide-by-zero on
shutdown of TCP_SYN_RECV sockets
On 10/29/24 08:03, Joel GUITTET wrote:
> We would like to ask your advice about the CVE-2024-36905 (tcp shutdown vulnerability).
> NIST indicates a network vector while AWS and Red Hat indicates local attack vector.
> Our cybersecurity team has difficulties to justify that a local vector is appropriate here.
> Can you help us to understand this specific point for this CVE ? The hypothesis we have is that a TCP socket need to be open/closed quickly, and maybe it's not possible remotely ?
From my understanding of Git commit
94062790aedb505bdda209b10bea47b294d6394f
(<URL:https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=94062790aedb505bdda209b10bea47b294d6394f>),
this appears to be a race condition where a program (running locally)
calls connect(2) and then shutdown(2) without actually attempting to
transfer any data, with a further constraint that certain packets (I am
unsure precisely what) must have been transferred such that the TCP
connection is half-opened. It *might* be possible to cause this crash
remotely if a program attempts to set up a unidirectional TCP connection
(achieved by shutting down the undesired direction) but I am unsure if
any such programs are actually in use.
I would need to further study the Linux networking code to be sure, but
a comment updated in the patch seems to imply that this is an edge case
that was previously believed to be impossible to reach. I suspect NIST
labeled it "network" because TCP is involved, but as of this writing
<URL:https://nvd.nist.gov/vuln/detail/CVE-2024-36905> says "This
vulnerability is currently awaiting analysis." so I would expect NIST's
indication to be revised after that analysis is completed.
Again, this issue is probably only remotely exploitable if the host is
running a very unusual client program, but a local exploit can supply
the required oddly-behaving program.
-- Jacob
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