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CVE-2026-80842 json

net: bridge: mcast: fix use-after-free of a master VLAN's multicast context

published 2mo ago modified 23d ago also EUVD-2026-71292

cvss
—
not scored
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 7%
public exploits
0
none known

Summary

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

net: bridge: mcast: fix use-after-free of a master VLAN's multicast context

br_multicast_toggle_one_vlan() clears BR_VLFLAG_MCAST_ENABLED under br->multicast_lock before stopping a VLAN's multicast context. That is the teardown handshake: lockless readers gate on the flag through br_multicast_ctx_should_use() -> br_multicast_ctx_vlan_disabled(), so once it is cleared under the lock no reader can arm the context again.

For a master VLAN the handshake never runs. __vlan_del() clears BRIDGE_VLAN_INFO_BRENTRY before calling br_vlan_put_master(), so br_multicast_toggle_one_vlan(masterv, false) returns early on !br_vlan_is_brentry(vlan): the flag stays set and br->multicast_lock is never taken. br_vlan_put_master() then drains the context in br_multicast_ctx_deinit() and frees the VLAN through call_rcu(), while a reader still inside rcu_read_lock() sees the context as enabled and re-arms it. The port and port-VLAN branch of the function has no br_vlan_is_brentry() test and flips the flag under br->multicast_lock, so it is not affected.

The reader is the bridge transmit path. For a master VLAN br_multicast_rcv() selects brmctx = &vlan->br_mcast_ctx with pmctx = NULL, so IGMP sent to the bridge device re-arms the context's timers after br_multicast_ctx_deinit() has already stopped them.

BUG: KASAN: slab-use-after-free in detach_if_pending+0x412/0x4a0 Write of size 8 at addr ffff88810ac39918 by task brmc/601 __mod_timer+0x51a/0xc50 br_multicast_host_join+0x25b/0x390 __br_multicast_add_group+0x468/0x530 br_ip4_multicast_add_group+0x1a0/0x260 br_multicast_rcv+0x2cda/0x61e0 br_dev_xmit+0x6c4/0x1540 Allocated by task 610: br_vlan_add+0x111/0xb40 br_vlan_info+0x370/0x3e0 Freed by task 0: kfree+0x1a7/0x4f0 rcu_core+0x7dc/0x10a0

Only test br_vlan_is_brentry() when enabling, like the br_multicast_ctx_vlan_global_disabled() test next to it. Disabling then always clears BR_VLFLAG_MCAST_ENABLED under br->multicast_lock before br_multicast_ctx_deinit() drains the context.

Patch / fix

  • Linux Linux 5.15.220, 6.1.187, 6.6.156, 6.12.108, 6.18.49, 7.1.13, 7.2.3, 7.3
  • linux Debian 12 6.1.187-1
  • linux Debian 13 6.12.111-1
  • linux Debian 14 7.1.13-1
  • linux-6.12 Debian 12 6.12.111-1~deb12u1

debian advisories DEBIAN-CVE-2026-80842

  • linux Ubuntu 22.04 LTS 5.15.0-202.212
  • linux Ubuntu 24.04 LTS 6.8.0-149.149
  • linux Ubuntu 26.04 LTS 7.0.0-42.42
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1119.126
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1069.74
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1016.17
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1120.130
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1073.81

ubuntu advisories UBUNTU-CVE-2026-80842

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 SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.84.1
  • kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.53.84.1
  • kernel-source SLE Module for Development Tools 15 SP7, SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1
  • kernel-default SLE Workstation Extension 15 SP7, SLE Module for Legacy 15 SP7, SLE Module for Basesystem 15 SP7 +2 more 6.4.0-150700.53.84.1
  • kernel-zfcpdump SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1
  • kernel-obs-build SLE Module for Development Tools 15 SP7 6.4.0-150700.53.84.1
  • kernel-default-base SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1.150700.17.47.1

suse advisories SUSE-SU-2026:4706-1SUSE-SU-2026:4640-1SUSE-SU-2026:24316-1SUSE-SU-2026:24315-1SUSE-SU-2026:24181-1SUSE-SU-2026:24182-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.39.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.39.1

opensuse advisories openSUSE-SU-2026:22091-1openSUSE-SU-2026:11773-1

  • kernel Azure Linux 3.0 6.6.157.1-1

azure linux advisories AZL-99528

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

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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-2026-80842 updated cvss 7.0

kernel: net: bridge: mcast: fix use-after-free of a master VLAN's multicast context

  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: workaround, no fix available
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    under investigation
  • Red Hat Enterprise Linux AppStream EUS (v.10.2) rv 6.12.0-211.75.1.el10_2, perf 6.12.0-211.75.1.el10_2, rtla 6.12.0-211.75.1.el10_2, python3-perf 6.12.0-211.75.1.el10_2, kernel-devel-matched 6.12.0-211.75.1.el10_2, kernel-64k-devel-matched 6.12.0-211.75.1.el10_2, +7 more
    fixed: vendor fix RHSA-2026:99139
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.185.1.el8_10, kernel 4.18.0-553.185.1.el8_10, bpftool 4.18.0-553.185.1.el8_10, kernel-core 4.18.0-553.185.1.el8_10, kernel-tools 4.18.0-553.185.1.el8_10, python3-perf 4.18.0-553.185.1.el8_10, +15 more
    fixed: vendor fix RHSA-2026:98099
  • Red Hat Enterprise Linux BaseOS EUS (v.10.2) kernel 6.12.0-211.75.1.el10_2, kernel-64k 6.12.0-211.75.1.el10_2, kernel-core 6.12.0-211.75.1.el10_2, kernel-tools 6.12.0-211.75.1.el10_2, kernel-modules 6.12.0-211.75.1.el10_2, kernel-64k-core 6.12.0-211.75.1.el10_2, +28 more Red Hat Enterprise Linux CodeReady Linux Builder EUS (v.10.2) libperf 6.12.0-211.75.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.75.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.75.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.75.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.75.1.el10_2
    fixed: vendor fix RHSA-2026:99139
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.185.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.185.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.185.1.el8_10
    fixed: vendor fix RHSA-2026:98099
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.185.1.rt7.526.el8_10, kernel-rt-kvm 4.18.0-553.185.1.rt7.526.el8_10, kernel-rt-core 4.18.0-553.185.1.rt7.526.el8_10, kernel-rt-modules 4.18.0-553.185.1.rt7.526.el8_10, kernel-rt-debug-kvm 4.18.0-553.185.1.rt7.526.el8_10, kernel-rt-debug-core 4.18.0-553.185.1.rt7.526.el8_10, +4 more
    fixed: vendor fix RHSA-2026:98100
  • Red Hat Enterprise Linux Real Time EUS (v.10.2) kernel-rt 6.12.0-211.75.1.el10_2, kernel-rt-64k 6.12.0-211.75.1.el10_2, kernel-rt-core 6.12.0-211.75.1.el10_2, kernel-rt-modules 6.12.0-211.75.1.el10_2, kernel-rt-64k-core 6.12.0-211.75.1.el10_2, kernel-rt-debug-core 6.12.0-211.75.1.el10_2, +14 more Red Hat Enterprise Linux Real Time for NFV EUS (v.10.2) kernel-rt 6.12.0-211.75.1.el10_2, kernel-rt-core 6.12.0-211.75.1.el10_2, kernel-rt-modules 6.12.0-211.75.1.el10_2, kernel-rt-debug-core 6.12.0-211.75.1.el10_2, kernel-rt-modules-core 6.12.0-211.75.1.el10_2, kernel-rt-debug-modules 6.12.0-211.75.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:99139
show 2 more
  • Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.185.1.rt7.526.el8_10, kernel-rt-core 4.18.0-553.185.1.rt7.526.el8_10, kernel-rt-modules 4.18.0-553.185.1.rt7.526.el8_10, kernel-rt-debug-core 4.18.0-553.185.1.rt7.526.el8_10, kernel-rt-debug-modules 4.18.0-553.185.1.rt7.526.el8_10, kernel-rt-modules-extra 4.18.0-553.185.1.rt7.526.el8_10, +2 more
    fixed: vendor fix RHSA-2026:98100
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 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

Exploit prediction

0.18% chance of exploitation in the next 30 days, higher than 7% of all scored CVEs (FIRST EPSS, 2026-11-11).

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

Fencer Intel 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.