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Fencer Vulns
critical 9.8

CVE-2025-39946 in the critical feed json

tls: make sure to abort the stream if headers are bogus

published 2025-10-04 13 mo ago modified 2026-10-19 20 d ago also EUVD-2025-32393

cvss
9.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
10.3%
EPSS 10.3% chance of exploitation in 30 days, percentile 95%
public exploits
0
none known

Summary

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

tls: make sure to abort the stream if headers are bogus

Normally we wait for the socket to buffer up the whole record before we service it. If the socket has a tiny buffer, however, we read out the data sooner, to prevent connection stalls. Make sure that we abort the connection when we find out late that the record is actually invalid. Retrying the parsing is fine in itself but since we copy some more data each time before we parse we can overflow the allocated skb space.

Constructing a scenario in which we're under pressure without enough data in the socket to parse the length upfront is quite hard. syzbot figured out a way to do this by serving us the header in small OOB sends, and then filling in the recvbuf with a large normal send.

Make sure that tls_rx_msg_size() aborts strp, if we reach an invalid record there's really no way to recover.

Patch / fix

  • Linux Linux 6.1.154, 6.6.108, 6.12.49, 6.16.9, 6.17
  • linux Debian 12 6.1.158-1
  • linux Debian 13 6.12.57-1
  • linux Debian 14 6.16.9-1

debian advisories DEBIAN-CVE-2025-39946

  • linux Ubuntu 24.04 LTS 6.8.0-100.100
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1046.49
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1047.50
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1043.48
  • linux-ibm Ubuntu 24.04 LTS 6.8.0-1044.44
  • linux-azure Ubuntu 24.04 LTS 6.8.0-1046.52
  • linux-gkeop Ubuntu 24.04 LTS 6.8.0-1030.33
  • linux-raspi Ubuntu 24.04 LTS 6.8.0-1047.51

ubuntu advisories UBUNTU-CVE-2025-39946

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 RHEL 10.1 6.12.0-124.11.1.el10_1
  • rv RHEL 10.1 6.12.0-124.11.1.el10_1
  • perf RHEL 10.1 6.12.0-124.11.1.el10_1
  • rtla RHEL 10.1 6.12.0-124.11.1.el10_1
  • libperf RHEL 10.1 6.12.0-124.11.1.el10_1
  • kernel-rt RHEL 10.1 6.12.0-124.11.1.el10_1
  • kernel-64k RHEL 10.1 6.12.0-124.11.1.el10_1
  • kernel-core RHEL 10.1 6.12.0-124.11.1.el10_1

red hat advisories RHSA-2025:21463

  • kernel-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.58.1
  • kernel-syms-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.58.1
  • kernel-rt_debug Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.58.1
  • kernel-source-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.58.1
  • kernel-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-38.1
  • kernel-source-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-38.1
  • kernel-rt Linux Micro 6.2 6.12.0-160000.6.1
  • kernel-64kb SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1

suse advisories SUSE-SU-2025:4301-1SUSE-SU-2025:21052-1SUSE-SU-2025:21064-1SUSE-SU-2025:21074-1SUSE-SU-2025:21139-1SUSE-SU-2026:20560-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.6.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-kvmsmall openSUSE Leap 16.0 6.12.0-160000.6.1

opensuse advisories openSUSE-SU-2025:20081-1

  • kernel Azure Linux 3.0 6.6.112.1-1

azure linux advisories AZL-68141

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

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-2025-39946 updated cvss 6.4

kernel: tls: make sure to abort the stream if headers are bogus

  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    affected: workaround, no fix available “To mitigate this issue, prevent module tls from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically.”
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-124.11.1.el10_1, perf 6.12.0-124.11.1.el10_1, rtla 6.12.0-124.11.1.el10_1, python3-perf 6.12.0-124.11.1.el10_1, kernel-devel-matched 6.12.0-124.11.1.el10_1, kernel-64k-devel-matched 6.12.0-124.11.1.el10_1, +7 more Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-124.11.1.el10_1, kernel-64k 6.12.0-124.11.1.el10_1, kernel-core 6.12.0-124.11.1.el10_1, kernel-tools 6.12.0-124.11.1.el10_1, kernel-modules 6.12.0-124.11.1.el10_1, kernel-64k-core 6.12.0-124.11.1.el10_1, +28 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-124.11.1.el10_1, kernel-debuginfo-common-s390x 6.12.0-124.11.1.el10_1, kernel-debuginfo-common-x86_64 6.12.0-124.11.1.el10_1, kernel-debuginfo-common-aarch64 6.12.0-124.11.1.el10_1, kernel-debuginfo-common-ppc64le 6.12.0-124.11.1.el10_1 Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-124.11.1.el10_1, kernel-rt-64k 6.12.0-124.11.1.el10_1, kernel-rt-core 6.12.0-124.11.1.el10_1, kernel-rt-modules 6.12.0-124.11.1.el10_1, kernel-rt-64k-core 6.12.0-124.11.1.el10_1, kernel-rt-debug-core 6.12.0-124.11.1.el10_1, +14 more Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-124.11.1.el10_1, kernel-rt-core 6.12.0-124.11.1.el10_1, kernel-rt-modules 6.12.0-124.11.1.el10_1, kernel-rt-debug-core 6.12.0-124.11.1.el10_1, kernel-rt-modules-core 6.12.0-124.11.1.el10_1, kernel-rt-debug-modules 6.12.0-124.11.1.el10_1, +4 more
    fixed: vendor fix “To mitigate this issue, prevent module tls from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically.” RHSA-2025:21463
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more
    not affected: vulnerable code not present

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
yes
Technical impact
total
Assessed
4 mo ago

Exploit prediction

10.26% chance of exploitation in the next 30 days, higher than 95% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

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.