CVE-2026-64109

What it is

In the Linux kernel, the following vulnerability has been resolved: af_unix: Fix UAF read of tail->len in unix_stream_data_wait() unix_stream_data_wait() does skb_peek_tail(&sk->sk_receive_queue) without holding any lock that prevents SKBs on that queue from being dequeued and freed. This has been the case since commit 79f632c71bea ("unix/stream: fix peeking with an offset larger than data in queue"). The first consequence of this is that the pointer comparison `tail != last` can be false even if `last` semantically refers to an already-freed SKB while `tail` is a new SKB allocated at the same address; which can cause unix_stream_data_wait() to wrongly keep blocking after new data has arrived, but only in a weird scenario where a peeking recv() and a normal recv() on the same socket are racing, which is probably not a real problem. But since commit 2b514574f7e8 ("net: af_unix: implement splice for stream af_unix sockets"), `tail` is actually dereferenced, which can cause UAF in the following race scenario (where test_setup() runs single-threaded, and afterwards, test_thread1() and test_thread2() run concurrently in two threads: ``` static int socks[2]; void test_setup(void) { socketpair(AF_UNIX, SOCK_STREAM, 0, socks); send(socks[1], "A", 1, 0); int peekoff = 1; setsockopt(socks[0], SOL_SOCKET, SO_PEEK_OFF, &peekoff, sizeof(peekoff)); } void test_thread1(void) { char dummy; recv(socks[0], &dummy, 1, MSG_PEEK); } void test_thread2(void) { char dummy; recv(socks[0], &dummy, 1, 0); shutdown(socks[1], SHUT_WR); } ``` when racing like this: ``` thread1 thread2 unix_stream_read_generic mutex_lock(&u->iolock) skb_peek(&sk->sk_receive_queue) skb_peek_next(skb, &sk->sk_receive_queue) mutex_unlock(&u->iolock) unix_stream_read_generic unix_state_lock(sk) skb_peek(&sk->sk_receive_queue) unix_state_unlock(sk) unix_stream_data_wait unix_state_lock(sk) tail = skb_peek_tail(&sk->sk_receive_queue) spin_lock(&sk->sk_receive_queue.lock) __skb_unlink(skb, &sk->sk_receive_queue) spin_unlock(&sk->sk_receive_queue.lock) consume_skb(skb) [frees the SKB] `tail != last`: false `tail`: true `tail->len != last_len` ***UAF*** ``` Fix the UAF by removing the read of tail->len; checking tail->len would only make sense if SKBs in the receive queue of a UNIX socket could grow, which can no longer happen. Kuniyuki explained: > When commit 869e7c62486e ("net: af_unix: implement stream sendpage > support") added sendpage() support, data could be appended to the last > skb in the receiver's queue. > > That's why we needed to check if the length of the last skb was changed > while waiting for new data in unix_stream_data_wait(). > > However, commit a0dbf5f818f9 ("af_unix: Support MSG_SPLICE_PAGES") and > commit 57d44a354a43 ("unix: Convert unix_stream_sendpage() to use > MSG_SPLICE_PAGES") refactored sendmsg(), and now data is always added > to a new skb. That means this fix is not suitable for kernels before 6.5.

At a glance

Exploitability

Can be exploited locally on the machine with a low-privilege account. High risk of data exposure, data tampering, service disruption.

Exploit odds

0.1% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-07-19 16:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-19 21:17 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.1% in the next 30 days (EPSS).
• Severity: 8.8 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-07-19 16:17 UTC

Last modified

2026-10-19 21:17 UTC

Exploit probability

0.1% · EPSS, next 30 days

Weakness

CWE-416 · Use after free

Record status

Modified

Affected

• Linux Kernel < 6.6.143
• Linux Kernel < 6.12.92
• Linux Kernel < 6.18.34
• Linux Kernel < 7.0.11
• Linux Kernel 7.1

Attack profile CVSS 3.1 · 8.8

Attack vector

Local

Complexity

Low

Privileges needed

Low

User interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

Is it in your code?

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