CVE-2026-68300: sctp: auth: verify auth requirement when auth_chunk is NULL

From: Greg Kroah-Hartman <[email protected]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

sctp: auth: verify auth requirement when auth_chunk is NULL

sctp_auth_chunk_verify() returns true unconditionally when
chunk->auth_chunk is NULL, silently skipping authentication.
This is incorrect when:

1. skb_clone() failed in the BH receive path, leaving auth_chunk
   NULL. In sctp_endpoint_bh_rcv() asoc is NULL for new
   connections, so the early sctp_auth_recv_cid() check cannot
   catch this.

2. No AUTH chunk precedes COOKIE-ECHO, so skb_clone() is never
   called and auth_chunk remains NULL.

Fix by checking sctp_auth_recv_cid() when auth_chunk is NULL:
if authentication is required, return false to drop the chunk;
otherwise continue normally.

The Linux kernel CVE team has assigned CVE-2026-68300 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.24 with commit bbd0d59809f923ea2b540cbd781b32110e249f6e and fixed in 6.6.148 with commit ec2e157fc9678a9bc411305a25aec3fd337d7efb
	Issue introduced in 2.6.24 with commit bbd0d59809f923ea2b540cbd781b32110e249f6e and fixed in 6.12.101 with commit 28c5fdce9dd955d2baf5e28987819b6d7cfaf646
	Issue introduced in 2.6.24 with commit bbd0d59809f923ea2b540cbd781b32110e249f6e and fixed in 6.18.42 with commit 18957373920caf5cdaf5cf32e5d1d7a99ca7700a
	Issue introduced in 2.6.24 with commit bbd0d59809f923ea2b540cbd781b32110e249f6e and fixed in 7.1.6 with commit 83f5031f2a6a49d696eb4cc0898345d12f9c6451
	Issue introduced in 2.6.24 with commit bbd0d59809f923ea2b540cbd781b32110e249f6e and fixed in 7.2-rc5 with commit 8e04823c120b376ef7dab14b60ebf6823aa16c14

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-68300
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/sctp/sm_statefuns.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/ec2e157fc9678a9bc411305a25aec3fd337d7efb
	https://git.kernel.org/stable/c/28c5fdce9dd955d2baf5e28987819b6d7cfaf646
	https://git.kernel.org/stable/c/18957373920caf5cdaf5cf32e5d1d7a99ca7700a
	https://git.kernel.org/stable/c/83f5031f2a6a49d696eb4cc0898345d12f9c6451
	https://git.kernel.org/stable/c/8e04823c120b376ef7dab14b60ebf6823aa16c14