linux-cve-announce - CVE-2025-39764: netfilter: ctnetlink: remove refcounting in expectation dumpers

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Message-ID: <2025091147-CVE-2025-39764-b300@gregkh>
Date: Thu, 11 Sep 2025 18:53:04 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-39764: netfilter: ctnetlink: remove refcounting in expectation dumpers

From: Greg Kroah-Hartman <gregkh@...nel.org>

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

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

netfilter: ctnetlink: remove refcounting in expectation dumpers

Same pattern as previous patch: do not keep the expectation object
alive via refcount, only store a cookie value and then use that
as the skip hint for dump resumption.

AFAICS this has the same issue as the one resolved in the conntrack
dumper, when we do
  if (!refcount_inc_not_zero(&exp->use))

to increment the refcount, there is a chance that exp == last, which
causes a double-increment of the refcount and subsequent memory leak.

The Linux kernel CVE team has assigned CVE-2025-39764 to this issue.


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

	Issue introduced in 2.6.23 with commit cf6994c2b9812a9f02b99e89df411ffc5db9c779 and fixed in 6.16.2 with commit a4d634ded4d3d400f115d84f654f316f249531c9
	Issue introduced in 2.6.23 with commit cf6994c2b9812a9f02b99e89df411ffc5db9c779 and fixed in 6.17-rc2 with commit 1492e3dcb2be3aa46d1963da96aa9593e4e4db5a

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-2025-39764
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/netfilter/nf_conntrack_netlink.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/a4d634ded4d3d400f115d84f654f316f249531c9
	https://git.kernel.org/stable/c/1492e3dcb2be3aa46d1963da96aa9593e4e4db5a