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Fencer Vulns
high 8.8

CVE-2026-64109 json

af_unix: Fix UAF read of tail->len in unix_stream_data_wait()

published 2026-07-19 3 mo ago modified 2026-10-19 20 d ago also EUVD-2026-45794

cvss
8.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 2%
public exploits
0
none known

Summary

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.

Patch / fix

  • Linux Linux 6.6.143, 6.12.92, 6.18.34, 7.0.11, 7.1
  • linux Debian 13 6.12.94-1
  • linux Debian 14 7.0.12-1

debian advisories DEBIAN-CVE-2026-64109

  • linux Ubuntu 24.04 LTS 6.8.0-139.139
  • linux Ubuntu 26.04 LTS 7.0.0-28.28
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1064.67
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1009.9
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1067.75
  • linux-gcp Ubuntu 26.04 LTS 7.0.0-1008.8
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1062.70
  • linux-gke Ubuntu 26.04 LTS 7.0.0-1003.4

ubuntu advisories UBUNTU-CVE-2026-64109

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-64kb SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS, SLE High Performance Computing 15 SP5-ESPOS 5.14.21-150500.55.189.1
  • kernel-syms SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.189.1
  • kernel-source SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.189.1
  • kernel-default SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +3 more 5.14.21-150500.55.189.1
  • kernel-obs-build SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.189.1
  • kernel-default-base SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.189.1.150500.6.87.4
  • kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.81.1
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.81.1

suse advisories SUSE-SU-2026:4595-1SUSE-SU-2026:4254-1SUSE-SU-2026:4369-1SUSE-SU-2026:4347-1SUSE-SU-2026:4284-1SUSE-SU-2026:23887-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.38.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.38.1

opensuse advisories openSUSE-SU-2026:21910-1

  • kernel AlmaLinux 8 4.18.0-553.181.1.el8_10
  • perf AlmaLinux 8 4.18.0-553.181.1.el8_10
  • bpftool AlmaLinux 8 4.18.0-553.181.1.el8_10
  • kernel-core AlmaLinux 8 4.18.0-553.181.1.el8_10
  • kernel-tools AlmaLinux 8 4.18.0-553.181.1.el8_10
  • python3-perf AlmaLinux 8 4.18.0-553.181.1.el8_10
  • kernel-modules AlmaLinux 8 4.18.0-553.181.1.el8_10
  • kernel-zfcpdump AlmaLinux 8 4.18.0-553.181.1.el8_10

almalinux advisories ALSA-2026:93436ALSA-2026:93437ALSA-2026:91565

  • kernel Rocky Linux 10 6.12.0-211.69.1.el10_2

rocky linux advisories RLSA-2026:91565

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-64109 updated cvss 4.7

kernel: af_unix: Fix UAF read of tail->len in unix_stream_data_wait()

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    affected: workaround, no fix available
  • Red Hat Enterprise Linux kernel-modules-internal 6.12.0-211.69.1.el10_2 Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-211.69.1.el10_2, perf 6.12.0-211.69.1.el10_2, rtla 6.12.0-211.69.1.el10_2, python3-perf 6.12.0-211.69.1.el10_2, kernel-devel-matched 6.12.0-211.69.1.el10_2, kernel-64k-devel-matched 6.12.0-211.69.1.el10_2, +7 more
    fixed: vendor fix RHSA-2026:91565
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.181.1.el8_10, kernel 4.18.0-553.181.1.el8_10, bpftool 4.18.0-553.181.1.el8_10, kernel-core 4.18.0-553.181.1.el8_10, kernel-tools 4.18.0-553.181.1.el8_10, python3-perf 4.18.0-553.181.1.el8_10, +15 more
    fixed: vendor fix RHSA-2026:93436
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-211.69.1.el10_2, kernel-64k 6.12.0-211.69.1.el10_2, kernel-core 6.12.0-211.69.1.el10_2, kernel-tools 6.12.0-211.69.1.el10_2, kernel-modules 6.12.0-211.69.1.el10_2, kernel-64k-core 6.12.0-211.69.1.el10_2, +28 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-211.69.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.69.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.69.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.69.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.69.1.el10_2
    fixed: vendor fix RHSA-2026:91565
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.181.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.181.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.181.1.el8_10
    fixed: vendor fix RHSA-2026:93436
  • Red Hat Enterprise Linux Hidden (v. 10) kernel-modules-internal 6.12.0-211.69.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.69.1.el10_2
    fixed: vendor fix RHSA-2026:91565
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.181.1.rt7.522.el8_10, kernel-rt-kvm 4.18.0-553.181.1.rt7.522.el8_10, kernel-rt-core 4.18.0-553.181.1.rt7.522.el8_10, kernel-rt-modules 4.18.0-553.181.1.rt7.522.el8_10, kernel-rt-debug-kvm 4.18.0-553.181.1.rt7.522.el8_10, kernel-rt-debug-core 4.18.0-553.181.1.rt7.522.el8_10, +4 more
    fixed: vendor fix RHSA-2026:93437
show 2 more
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-211.69.1.el10_2, kernel-rt-64k 6.12.0-211.69.1.el10_2, kernel-rt-core 6.12.0-211.69.1.el10_2, kernel-rt-modules 6.12.0-211.69.1.el10_2, kernel-rt-64k-core 6.12.0-211.69.1.el10_2, kernel-rt-debug-core 6.12.0-211.69.1.el10_2, +14 more Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-211.69.1.el10_2, kernel-rt-core 6.12.0-211.69.1.el10_2, kernel-rt-modules 6.12.0-211.69.1.el10_2, kernel-rt-debug-core 6.12.0-211.69.1.el10_2, kernel-rt-modules-core 6.12.0-211.69.1.el10_2, kernel-rt-debug-modules 6.12.0-211.69.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:91565
  • Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.181.1.rt7.522.el8_10, kernel-rt-core 4.18.0-553.181.1.rt7.522.el8_10, kernel-rt-modules 4.18.0-553.181.1.rt7.522.el8_10, kernel-rt-debug-core 4.18.0-553.181.1.rt7.522.el8_10, kernel-rt-debug-modules 4.18.0-553.181.1.rt7.522.el8_10, kernel-rt-modules-extra 4.18.0-553.181.1.rt7.522.el8_10, +2 more
    fixed: vendor fix RHSA-2026:93437

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
23 d ago

Exploit prediction

0.13% chance of exploitation in the next 30 days, higher than 2% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 8.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Affected products

  • Linux Linux

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.