Unknown

CVE-2026-80842 — net: bridge: mcast: fix use-after-free of a master VLAN's multicast context

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.

Published Sep 4, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: Linux

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.2% (30-day exploitation probability)+1

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.18%

ahead of 7% of scored CVEs · Oct 27, 2026

Affects

Linux

CVSS base

—

Score not published yet.

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Linux Linux).
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Linux	Linux	≥ 7b54aaaf53cb784411426c64482af0435f7c845e and < 3afaaee2f972aec9059110953adb62fa3cf5c4bd≥ 7b54aaaf53cb784411426c64482af0435f7c845e and < 22226a2c3b90f15b0925f1464470d3baa6c5677e≥ 7b54aaaf53cb784411426c64482af0435f7c845e and < 7c54fd8cfbcf371a5ef50db5c53fe6e85fb76686≥ 7b54aaaf53cb784411426c64482af0435f7c845e and < 3a0ad4fcdfa0b7dba1876de14a12cb65c8b5ca50≥ 7b54aaaf53cb784411426c64482af0435f7c845e and < c069f29da72324697aa4b7cab5b3647a7d24a575≥ 7b54aaaf53cb784411426c64482af0435f7c845e and < 3f4752996735e0628af559aa8da1d872c2fac13b≥ 7b54aaaf53cb784411426c64482af0435f7c845e and < 57f94d3f4dee8b54d63cefddf1112be4656ef9e6≥ 7b54aaaf53cb784411426c64482af0435f7c845e and < 50e5c6605cc9c2dd57bd2d1b3459674d19738983 and 1 more version 5.15	Vulnerable	CVE Program (cve.org) e CISA ADP

EPSS over time FIRST

Oct 15, 2026 → Oct 27, 2026 · 12 reading(s) · max 0.18%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Not enough vector or weakness data: use the affected application’s logs as a starting point.

application logs

Timeline

What happened to this CVE, newest first.

2026
Record published
Oct 15, 2026
Affected products added · linux/linux
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
Source status changed · → Received
Oct 15, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 15, 2026 · NIST National Vulnerability Database
CVE published
Sep 4, 2026 · Linux

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

8 on the record

git.kernel.org/stable/c/3afaaee2f972aec9059110953adb62fa3cf5c4bd
NIST National Vulnerability Database
git.kernel.org/stable/c/57f94d3f4dee8b54d63cefddf1112be4656ef9e6
NIST National Vulnerability Database
git.kernel.org/stable/c/7c54fd8cfbcf371a5ef50db5c53fe6e85fb76686
NIST National Vulnerability Database
git.kernel.org/stable/c/3f4752996735e0628af559aa8da1d872c2fac13b
NIST National Vulnerability Database
git.kernel.org/stable/c/3a0ad4fcdfa0b7dba1876de14a12cb65c8b5ca50
NIST National Vulnerability Database
git.kernel.org/stable/c/22226a2c3b90f15b0925f1464470d3baa6c5677e
NIST National Vulnerability Database
git.kernel.org/stable/c/50e5c6605cc9c2dd57bd2d1b3459674d19738983
NIST National Vulnerability Database
git.kernel.org/stable/c/c069f29da72324697aa4b7cab5b3647a7d24a575
NIST National Vulnerability Database

Elsewhere on this site

Linux
every CVE for this vendor

Related CVEs (same products)

Unknown CVE-2026-99100 wifi: p54: validate firmware record lengths 1h
Unknown CVE-2026-99092 riscv: patch: fix handling of bpf-jit execmem addresses 1d
Unknown CVE-2026-99093 mm: don't schedule deferred kernel page table freeing while booting 1d
Unknown CVE-2026-99095 drm/vc4: drain the hangcheck timer and works on V3D unbind 1d
Unknown CVE-2026-99096 io_uring/register: don't exempt disabled rings from task restrictions 1d
Unknown CVE-2026-99097 tee: shm: reject zero-sized allocations in tee_dyn_shm_alloc_helper() 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No CVSS score published by NVD, the CNA, CISA or GitHub so far.
No fixed version, patch or mitigation documented.
No CISA SSVC assessment.
No CWE classification.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-80842 is "net: bridge: mcast: fix use-after-free of a master VLAN's multicast context", rated Unknown. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. EPSS 0.18% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

Comments

Moderated technical discussion. Read the community guidelines.

No comments yet.