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Fencer Vulns
high 7.8

CVE-2025-39766 json

net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit

published 2025-09-11 13 mo ago modified 2026-10-19 20 d ago also EUVD-2025-28946

cvss
7.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 8%
public exploits
0
none known

Summary

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

net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit

The following setup can trigger a WARNING in htb_activate due to the condition: !cl->leaf.q->q.qlen

tc qdisc del dev lo root tc qdisc add dev lo root handle 1: htb default 1 tc class add dev lo parent 1: classid 1:1 \ htb rate 64bit tc qdisc add dev lo parent 1:1 handle f: \ cake memlimit 1b ping -I lo -f -c1 -s64 -W0.001 127.0.0.1

This is because the low memlimit leads to a low buffer_limit, which causes packet dropping. However, cake_enqueue still returns NET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an empty child qdisc. We should return NET_XMIT_CN when packets are dropped from the same tin and flow.

I do not believe return value of NET_XMIT_CN is necessary for packet drops in the case of ack filtering, as that is meant to optimize performance, not to signal congestion.

Patch / fix

  • Linux Linux 5.4.297, 5.10.241, 5.15.190, 6.1.149, 6.6.103, 6.12.44, 6.16.4, 6.17
  • Siemens SIMATIC CN 4100 V5.0
  • linux Debian 12 6.1.153-1
  • linux Debian 13 6.12.48-1
  • linux Debian 14 6.16.5-1

debian advisories DEBIAN-CVE-2025-39766

  • linux Ubuntu 22.04 LTS 5.15.0-163.173
  • linux Ubuntu 24.04 LTS 6.8.0-100.100
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1097.104
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1046.49
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1097.106
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1047.50
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1093.99
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1043.48

ubuntu advisories UBUNTU-CVE-2025-39766

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 10.2 6.12.0-211.16.1.el10_2
  • rv RHEL 10.2 6.12.0-211.16.1.el10_2
  • perf RHEL 10.2 6.12.0-211.16.1.el10_2
  • rtla RHEL 10.2 6.12.0-211.16.1.el10_2
  • libperf RHEL 10.2 6.12.0-211.16.1.el10_2
  • kernel-rt RHEL 10.2 6.12.0-211.16.1.el10_2
  • kernel-64k RHEL 10.2 6.12.0-211.16.1.el10_2
  • kernel-core RHEL 10.2 6.12.0-211.16.1.el10_2

red hat advisories RHSA-2026:23224RHSA-2026:22940RHSA-2026:22900RHSA-2026:22334RHSA-2026:21209RHSA-2026:19569

  • 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
  • kernel-source SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1
  • kernel-default SLES 16.0, SLE High Availability Extension 16.0, Linux Micro 6.2 +1 more 6.12.0-160000.6.1
  • kernel-default-base SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1.160000.2.4
  • kernel-syms SLES 16.0, Linux Micro Extras 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1
  • kernel-obs-qa SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.6.1
  • kernel-kvmsmall SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.6.1

suse advisories SUSE-SU-2025:21074-1SUSE-SU-2025:21139-1SUSE-SU-2026:20560-1SUSE-SU-2025:21179-1SUSE-SU-2025:20870-1SUSE-SU-2025:20898-1

  • 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 AlmaLinux 9 5.14.0-687.10.1.el9_8
  • rv AlmaLinux 9 5.14.0-687.10.1.el9_8
  • perf AlmaLinux 9 5.14.0-687.10.1.el9_8
  • rtla AlmaLinux 9 5.14.0-687.10.1.el9_8
  • libperf AlmaLinux 9 5.14.0-687.10.1.el9_8
  • kernel-rt AlmaLinux 9 5.14.0-687.10.1.el9_8
  • kernel-64k AlmaLinux 9 5.14.0-687.10.1.el9_8
  • kernel-core AlmaLinux 9 5.14.0-687.10.1.el9_8

almalinux advisories ALSA-2026:19568ALSA-2026:19569ALSA-2026:9264ALSA-2026:8921

  • kernel Rocky Linux 10 6.12.0-211.16.1.el10_2.0.1
  • kernel Rocky Linux 9 5.14.0-687.10.1.el9_8.0.1
  • kernel Rocky Linux 10 6.12.0-124.52.1.el10_1
  • kernel Rocky Linux 9 5.14.0-611.49.1.el9_7

rocky linux advisories RLSA-2026:19569RLSA-2026:19568RLSA-2026:9264RLSA-2026:8921

  • kernel Azure Linux 3.0 6.6.104.2-1
  • kernel CBL-Mariner 2.0 5.15.200.1-1

azure linux advisories AZL-67232AZL-73962

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-2025-39766 updated cvss 7.3

kernel: net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit

  • Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 more
    affected: no fix available
  • Red Hat CodeReady Linux Builder EUS (v.9.4) libperf 5.14.0-427.127.1.el9_4, kernel-debuginfo-common-s390x 5.14.0-427.127.1.el9_4, kernel-debuginfo-common-x86_64 5.14.0-427.127.1.el9_4, kernel-debuginfo-common-aarch64 5.14.0-427.127.1.el9_4, kernel-debuginfo-common-ppc64le 5.14.0-427.127.1.el9_4
    fixed: vendor fix RHSA-2026:21209
  • Red Hat CodeReady Linux Builder EUS (v.9.6) libperf 5.14.0-570.119.1.el9_6, kernel-debuginfo-common-s390x 5.14.0-570.119.1.el9_6, kernel-debuginfo-common-x86_64 5.14.0-570.119.1.el9_6, kernel-debuginfo-common-aarch64 5.14.0-570.119.1.el9_6, kernel-debuginfo-common-ppc64le 5.14.0-570.119.1.el9_6
    fixed: vendor fix RHSA-2026:23224
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-611.49.1.el9_7, rv 5.14.0-687.10.1.el9_8, perf 5.14.0-611.49.1.el9_7, perf 5.14.0-687.10.1.el9_8, rtla 5.14.0-611.49.1.el9_7, rtla 5.14.0-687.10.1.el9_8, +20 more
    fixed: vendor fix RHSA-2026:8921
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-124.52.1.el10_1, rv 6.12.0-211.16.1.el10_2, perf 6.12.0-124.52.1.el10_1, perf 6.12.0-211.16.1.el10_2, rtla 6.12.0-124.52.1.el10_1, rtla 6.12.0-211.16.1.el10_2, +20 more
    fixed: vendor fix RHSA-2026:9264
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) perf 5.14.0-284.174.1.el9_2, rtla 5.14.0-284.174.1.el9_2, kernel-devel-matched 5.14.0-284.174.1.el9_2, kernel-64k-devel-matched 5.14.0-284.174.1.el9_2, kernel-debug-devel-matched 5.14.0-284.174.1.el9_2, kernel-debuginfo-common-s390x 5.14.0-284.174.1.el9_2, +5 more
    fixed: vendor fix RHSA-2026:22940
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) rv 6.12.0-55.76.1.el10_0, perf 6.12.0-55.76.1.el10_0, rtla 6.12.0-55.76.1.el10_0, python3-perf 6.12.0-55.76.1.el10_0, kernel-devel-matched 6.12.0-55.76.1.el10_0, kernel-64k-devel-matched 6.12.0-55.76.1.el10_0, +7 more
    fixed: vendor fix RHSA-2026:22334
  • Red Hat Enterprise Linux AppStream EUS (v.9.4) rv 5.14.0-427.127.1.el9_4, perf 5.14.0-427.127.1.el9_4, rtla 5.14.0-427.127.1.el9_4, kernel-devel-matched 5.14.0-427.127.1.el9_4, kernel-64k-devel-matched 5.14.0-427.127.1.el9_4, kernel-debug-devel-matched 5.14.0-427.127.1.el9_4, +6 more
    fixed: vendor fix RHSA-2026:21209
show 23 more
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) rv 5.14.0-570.119.1.el9_6, perf 5.14.0-570.119.1.el9_6, rtla 5.14.0-570.119.1.el9_6, python3-perf 5.14.0-570.119.1.el9_6, kernel-devel-matched 5.14.0-570.119.1.el9_6, kernel-64k-devel-matched 5.14.0-570.119.1.el9_6, +7 more
    fixed: vendor fix RHSA-2026:23224
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-611.49.1.el9_7, kernel 5.14.0-687.10.1.el9_8, kernel-64k 5.14.0-611.49.1.el9_7, kernel-64k 5.14.0-687.10.1.el9_8, kernel-core 5.14.0-611.49.1.el9_7, kernel-core 5.14.0-687.10.1.el9_8, +60 more
    fixed: vendor fix RHSA-2026:8921
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-124.52.1.el10_1, kernel 6.12.0-211.16.1.el10_2, kernel-64k 6.12.0-124.52.1.el10_1, kernel-64k 6.12.0-211.16.1.el10_2, kernel-core 6.12.0-124.52.1.el10_1, kernel-core 6.12.0-211.16.1.el10_2, +62 more
    fixed: vendor fix RHSA-2026:9264
  • Red Hat Enterprise Linux BaseOS E4S (v.9.2) bpftool 7.0.0-284.174.1.el9_2, kernel 5.14.0-284.174.1.el9_2, kernel-64k 5.14.0-284.174.1.el9_2, kernel-core 5.14.0-284.174.1.el9_2, kernel-tools 5.14.0-284.174.1.el9_2, python3-perf 5.14.0-284.174.1.el9_2, +28 more
    fixed: vendor fix RHSA-2026:22940
  • Red Hat Enterprise Linux BaseOS EUS (v. 10.0) kernel 6.12.0-55.76.1.el10_0, kernel-64k 6.12.0-55.76.1.el10_0, kernel-core 6.12.0-55.76.1.el10_0, kernel-tools 6.12.0-55.76.1.el10_0, kernel-modules 6.12.0-55.76.1.el10_0, kernel-64k-core 6.12.0-55.76.1.el10_0, +27 more
    fixed: vendor fix RHSA-2026:22334
  • Red Hat Enterprise Linux BaseOS EUS (v.9.4) bpftool 7.3.0-427.127.1.el9_4, kernel 5.14.0-427.127.1.el9_4, kernel-64k 5.14.0-427.127.1.el9_4, kernel-core 5.14.0-427.127.1.el9_4, kernel-tools 5.14.0-427.127.1.el9_4, python3-perf 5.14.0-427.127.1.el9_4, +28 more
    fixed: vendor fix RHSA-2026:21209
  • Red Hat Enterprise Linux BaseOS EUS (v.9.6) kernel 5.14.0-570.119.1.el9_6, kernel-64k 5.14.0-570.119.1.el9_6, kernel-core 5.14.0-570.119.1.el9_6, kernel-tools 5.14.0-570.119.1.el9_6, kernel-modules 5.14.0-570.119.1.el9_6, kernel-64k-core 5.14.0-570.119.1.el9_6, +27 more
    fixed: vendor fix RHSA-2026:23224
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-611.49.1.el9_7, libperf 5.14.0-687.10.1.el9_8, kernel-debuginfo-common-s390x 5.14.0-611.49.1.el9_7, kernel-debuginfo-common-s390x 5.14.0-687.10.1.el9_8, kernel-debuginfo-common-x86_64 5.14.0-611.49.1.el9_7, kernel-debuginfo-common-x86_64 5.14.0-687.10.1.el9_8, +4 more
    fixed: vendor fix RHSA-2026:8921
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-124.52.1.el10_1, libperf 6.12.0-211.16.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-124.52.1.el10_1, kernel-debuginfo-common-s390x 6.12.0-211.16.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-124.52.1.el10_1, kernel-debuginfo-common-x86_64 6.12.0-211.16.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:9264
  • Red Hat Enterprise Linux CodeReady Linux Builder EUS (v. 10.0) libperf 6.12.0-55.76.1.el10_0, kernel-debuginfo-common-s390x 6.12.0-55.76.1.el10_0, kernel-debuginfo-common-x86_64 6.12.0-55.76.1.el10_0, kernel-debuginfo-common-aarch64 6.12.0-55.76.1.el10_0, kernel-debuginfo-common-ppc64le 6.12.0-55.76.1.el10_0
    fixed: vendor fix RHSA-2026:22334
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-611.49.1.el9_7, kernel-rt 5.14.0-687.10.1.el9_8, kernel-rt-64k 5.14.0-611.49.1.el9_7, kernel-rt-64k 5.14.0-687.10.1.el9_8, kernel-rt-core 5.14.0-611.49.1.el9_7, kernel-rt-core 5.14.0-687.10.1.el9_8, +34 more
    fixed: vendor fix RHSA-2026:8921
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-124.52.1.el10_1, kernel-rt 6.12.0-211.16.1.el10_2, kernel-rt-64k 6.12.0-124.52.1.el10_1, kernel-rt-64k 6.12.0-211.16.1.el10_2, kernel-rt-core 6.12.0-124.52.1.el10_1, kernel-rt-core 6.12.0-211.16.1.el10_2, +34 more
    fixed: vendor fix RHSA-2026:9264
  • Red Hat Enterprise Linux Real Time E4S (v.9.2) kernel-rt 5.14.0-284.174.1.rt14.459.el9_2, kernel-rt-core 5.14.0-284.174.1.rt14.459.el9_2, kernel-rt-modules 5.14.0-284.174.1.rt14.459.el9_2, kernel-rt-debug-core 5.14.0-284.174.1.rt14.459.el9_2, kernel-rt-modules-core 5.14.0-284.174.1.rt14.459.el9_2, kernel-rt-debug-modules 5.14.0-284.174.1.rt14.459.el9_2, +4 more
    fixed: vendor fix RHSA-2026:22900
  • Red Hat Enterprise Linux Real Time EUS (v. 10.0) kernel-rt 6.12.0-55.76.1.el10_0, kernel-rt-64k 6.12.0-55.76.1.el10_0, kernel-rt-core 6.12.0-55.76.1.el10_0, kernel-rt-modules 6.12.0-55.76.1.el10_0, kernel-rt-64k-core 6.12.0-55.76.1.el10_0, kernel-rt-debug-core 6.12.0-55.76.1.el10_0, +14 more
    fixed: vendor fix RHSA-2026:22334
  • Red Hat Enterprise Linux Real Time EUS (v.9.4) kernel-rt 5.14.0-427.127.1.el9_4, kernel-rt-core 5.14.0-427.127.1.el9_4, kernel-rt-modules 5.14.0-427.127.1.el9_4, kernel-rt-debug-core 5.14.0-427.127.1.el9_4, kernel-rt-modules-core 5.14.0-427.127.1.el9_4, kernel-rt-debug-modules 5.14.0-427.127.1.el9_4, +4 more
    fixed: vendor fix RHSA-2026:21209
  • Red Hat Enterprise Linux Real Time EUS (v.9.6) kernel-rt 5.14.0-570.119.1.el9_6, kernel-rt-64k 5.14.0-570.119.1.el9_6, kernel-rt-core 5.14.0-570.119.1.el9_6, kernel-rt-modules 5.14.0-570.119.1.el9_6, kernel-rt-64k-core 5.14.0-570.119.1.el9_6, kernel-rt-debug-core 5.14.0-570.119.1.el9_6, +14 more
    fixed: vendor fix RHSA-2026:23224
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-611.49.1.el9_7, kernel-rt 5.14.0-687.10.1.el9_8, kernel-rt-core 5.14.0-611.49.1.el9_7, kernel-rt-core 5.14.0-687.10.1.el9_8, kernel-rt-modules 5.14.0-611.49.1.el9_7, kernel-rt-modules 5.14.0-687.10.1.el9_8, +14 more
    fixed: vendor fix RHSA-2026:8921
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-124.52.1.el10_1, kernel-rt 6.12.0-211.16.1.el10_2, kernel-rt-core 6.12.0-124.52.1.el10_1, kernel-rt-core 6.12.0-211.16.1.el10_2, kernel-rt-modules 6.12.0-124.52.1.el10_1, kernel-rt-modules 6.12.0-211.16.1.el10_2, +14 more
    fixed: vendor fix RHSA-2026:9264
  • Red Hat Enterprise Linux Real Time for NFV E4S (v.9.2) kernel-rt 5.14.0-284.174.1.rt14.459.el9_2, kernel-rt-kvm 5.14.0-284.174.1.rt14.459.el9_2, kernel-rt-core 5.14.0-284.174.1.rt14.459.el9_2, kernel-rt-modules 5.14.0-284.174.1.rt14.459.el9_2, kernel-rt-debug-kvm 5.14.0-284.174.1.rt14.459.el9_2, kernel-rt-debug-core 5.14.0-284.174.1.rt14.459.el9_2, +6 more
    fixed: vendor fix RHSA-2026:22900
  • Red Hat Enterprise Linux Real Time for NFV EUS (v. 10.0) kernel-rt 6.12.0-55.76.1.el10_0, kernel-rt-kvm 6.12.0-55.76.1.el10_0, kernel-rt-core 6.12.0-55.76.1.el10_0, kernel-rt-modules 6.12.0-55.76.1.el10_0, kernel-rt-debug-kvm 6.12.0-55.76.1.el10_0, kernel-rt-debug-core 6.12.0-55.76.1.el10_0, +6 more
    fixed: vendor fix RHSA-2026:22334
  • Red Hat Enterprise Linux Real Time for NFV EUS (v.9.4) kernel-rt 5.14.0-427.127.1.el9_4, kernel-rt-kvm 5.14.0-427.127.1.el9_4, kernel-rt-core 5.14.0-427.127.1.el9_4, kernel-rt-modules 5.14.0-427.127.1.el9_4, kernel-rt-debug-kvm 5.14.0-427.127.1.el9_4, kernel-rt-debug-core 5.14.0-427.127.1.el9_4, +6 more
    fixed: vendor fix RHSA-2026:21209
  • Red Hat Enterprise Linux Real Time for NFV EUS (v.9.6) kernel-rt 5.14.0-570.119.1.el9_6, kernel-rt-kvm 5.14.0-570.119.1.el9_6, kernel-rt-core 5.14.0-570.119.1.el9_6, kernel-rt-modules 5.14.0-570.119.1.el9_6, kernel-rt-debug-kvm 5.14.0-570.119.1.el9_6, kernel-rt-debug-core 5.14.0-570.119.1.el9_6, +6 more
    fixed: vendor fix RHSA-2026:23224
  • 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
no
Technical impact
total
Assessed
4 mo ago

Exploit prediction

0.18% chance of exploitation in the next 30 days, higher than 8% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Linux Linux
  • Siemens SIMATIC CN 4100

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.