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Fencer Vulns
high 7.8

CVE-2026-74583 json

net/sched: cls_route: fix fastmap use-after-free on filter

published 2026-08-21 2 mo ago modified 2026-10-16 23 d ago also EUVD-2026-64005

cvss
7.8
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 1%
public exploits
0
none known

Summary

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

net/sched: cls_route: fix fastmap use-after-free on filter

The route4 classifier maintains a 16-slot fastmap cache that stores raw struct route4_filter pointers indexed by (id, iif). The reader (route4_classify) populates this cache via route4_set_fastmap() for every classified packet that hits a filter. The writer (route4_delete, route4_change) clears the cache via route4_reset_fastmap() before RCU-deferred kfree of the filter.

This creates a UAF race: 1. Reader walks the RCU-protected bucket chain, finds filter f 2. Writer unlinks f, calls route4_reset_fastmap(), then tcf_queue_work() 3. Reader calls route4_set_fastmap() and writes f into the cache *after* the writer's reset, caching a pointer about to be freed 4. After the RCU grace period, kfree(f) executes 5. Next classified packet on the same (id, iif) tuple hits the stale fastmap entry and reads f->res from freed memory

Reproduced with an mdelay(100) accelerator in route4_set_fastmap() and a concurrent add/delete stress test (provided by both zdi and Santosh). Both triggered KASAN slab-use-after-free reports in the route4 fastmap paths.

Fix: Introduce a per-filter boolean dying flag to suppress stale fastmap republishing by in-flight readers.

Patch / fix

  • Linux Linux 5.10.265, 5.15.216, 6.1.183, 6.6.152, 6.12.104, 6.18.45, 7.1.9, 7.2
  • linux Debian 12 6.1.187-1
  • linux Debian 13 6.12.105-1
  • linux Debian 14 7.1.9-1
  • linux-6.12 Debian 12 6.12.107-1~deb12u1

debian advisories DEBIAN-CVE-2026-74583

  • linux Ubuntu 22.04 LTS 5.15.0-198.208
  • linux Ubuntu 26.04 LTS 7.0.0-42.42
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1117.124
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1016.17
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1118.128
  • linux-gcp Ubuntu 26.04 LTS 7.0.0-1016.18
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1113.119
  • linux-ibm Ubuntu 22.04 LTS 5.15.0-1111.115

ubuntu advisories UBUNTU-CVE-2026-74583

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 8 4.18.0-553.174.1.el8_10
  • perf RHEL 8 4.18.0-553.174.1.el8_10
  • bpftool RHEL 8 4.18.0-553.174.1.el8_10
  • kernel-core RHEL 8 4.18.0-553.174.1.el8_10
  • kernel-tools RHEL 8 4.18.0-553.174.1.el8_10
  • python3-perf RHEL 8 4.18.0-553.174.1.el8_10
  • kernel-modules RHEL 8 4.18.0-553.174.1.el8_10
  • kernel-zfcpdump RHEL 8 4.18.0-553.174.1.el8_10

red hat advisories RHSA-2026:83157RHSA-2026:83159

  • kernel-rt Real Time Module 15 SP7 6.4.0-150700.7.81.1
  • kernel-syms-rt Real Time Module 15 SP7 6.4.0-150700.7.81.1
  • kernel-source-rt Real Time Module 15 SP7 6.4.0-150700.7.81.1
  • kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.87.3
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.87.1
  • kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.53.87.3
  • kernel-source SLE Module for Development Tools 15 SP7, SLE Module for Basesystem 15 SP7 6.4.0-150700.53.87.3
  • kernel-default SLE Workstation Extension 15 SP7, SLE Module for Legacy 15 SP7, SLE Module for Basesystem 15 SP7 +2 more 6.4.0-150700.53.87.3

suse advisories SUSE-SU-2026:4940-1SUSE-SU-2026:4935-1SUSE-SU-2026:24473-1SUSE-SU-2026:24553-1SUSE-SU-2026:24422-1SUSE-SU-2026:24446-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.40.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.40.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.40.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.40.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.40.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.40.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.40.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.40.1

opensuse advisories openSUSE-SU-2026:22167-1

  • kernel AlmaLinux 8 4.18.0-553.174.1.el8_10
  • perf AlmaLinux 8 4.18.0-553.174.1.el8_10
  • bpftool AlmaLinux 8 4.18.0-553.174.1.el8_10
  • kernel-core AlmaLinux 8 4.18.0-553.174.1.el8_10
  • kernel-tools AlmaLinux 8 4.18.0-553.174.1.el8_10
  • python3-perf AlmaLinux 8 4.18.0-553.174.1.el8_10
  • kernel-modules AlmaLinux 8 4.18.0-553.174.1.el8_10
  • kernel-zfcpdump AlmaLinux 8 4.18.0-553.174.1.el8_10

almalinux advisories ALSA-2026:83157ALSA-2026:83159

  • kernel-rt Rocky Linux 8 4.18.0-553.174.1.rt7.515.el8_10
  • kernel Rocky Linux 8 4.18.0-553.174.1.el8_10

rocky linux advisories RLSA-2026:83159RLSA-2026:83157

  • kernel Azure Linux 3.0 6.6.152.1-1

azure linux advisories AZL-96998

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-2026-74583 updated cvss 7.8

kernel: net/sched: cls_route: fix fastmap use-after-free on filter

  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    affected: workaround, no fix available
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.174.1.el8_10, kernel 4.18.0-553.174.1.el8_10, bpftool 4.18.0-553.174.1.el8_10, kernel-core 4.18.0-553.174.1.el8_10, kernel-tools 4.18.0-553.174.1.el8_10, python3-perf 4.18.0-553.174.1.el8_10, +15 more Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.174.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.174.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.174.1.el8_10
    fixed: vendor fix RHSA-2026:83157
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.174.1.rt7.515.el8_10, kernel-rt-kvm 4.18.0-553.174.1.rt7.515.el8_10, kernel-rt-core 4.18.0-553.174.1.rt7.515.el8_10, kernel-rt-modules 4.18.0-553.174.1.rt7.515.el8_10, kernel-rt-debug-kvm 4.18.0-553.174.1.rt7.515.el8_10, kernel-rt-debug-core 4.18.0-553.174.1.rt7.515.el8_10, +4 more Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.174.1.rt7.515.el8_10, kernel-rt-core 4.18.0-553.174.1.rt7.515.el8_10, kernel-rt-modules 4.18.0-553.174.1.rt7.515.el8_10, kernel-rt-debug-core 4.18.0-553.174.1.rt7.515.el8_10, kernel-rt-debug-modules 4.18.0-553.174.1.rt7.515.el8_10, kernel-rt-modules-extra 4.18.0-553.174.1.rt7.515.el8_10, +2 more
    fixed: vendor fix RHSA-2026:83159
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel
    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
23 d ago

Exploit prediction

0.12% chance of exploitation in the next 30 days, higher than 1% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 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

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.