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NVD / CVE Program· CNA Linux

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

Noroxi assessment

Priority: Monitor (action score 0/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.17% (FIRST EPSS).
  • Fixed version: Linux Linux 22226a2c3b90f15b0925f1464470d3baa6c5677e, 3a0ad4fcdfa0b7dba1876de14a12cb65c8b5ca50, 3afaaee2f972aec9059110953adb62fa3cf5c4bd; azl3 kernel 6.6.152.1-1 on Azure Linux 3.0 6.6.157.1-1.

Low priority for now. Upgrade to Linux Linux 22226a2c3b90f15b0925f1464470d3baa6c5677e, 3a0ad4fcdfa0b7dba1876de14a12cb65c8b5ca50, 3afaaee2f972aec9059110953adb62fa3cf5c4bd; azl3 kernel 6.6.152.1-1 on Azure Linux 3.0 6.6.157.1-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

—No exploit Fix available
Published
Sep 4, 2026
Updated
Oct 19, 2026
EPSS
0.1% · 7th percentile
CWE
—

Report tools

JSON

Action score

0

Monitor

Low priority for now.

CVSS
0 / 40 · —
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

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Noroxi analysis

What does it mean in your environment?

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 5.15affected
    • 7b54aaaf53cb784411426c64482af0435f7c845e and later · before 3afaaee2f972aec9059110953adb62fa3cf5c4bdaffected · git
    • 7b54aaaf53cb784411426c64482af0435f7c845e and later · before 22226a2c3b90f15b0925f1464470d3baa6c5677eaffected · git
    • 7b54aaaf53cb784411426c64482af0435f7c845e and later · before 7c54fd8cfbcf371a5ef50db5c53fe6e85fb76686affected · git
    • 7b54aaaf53cb784411426c64482af0435f7c845e and later · before 3a0ad4fcdfa0b7dba1876de14a12cb65c8b5ca50affected · git
    • 7b54aaaf53cb784411426c64482af0435f7c845e and later · before c069f29da72324697aa4b7cab5b3647a7d24a575affected · git
    • 7b54aaaf53cb784411426c64482af0435f7c845e and later · before 3f4752996735e0628af559aa8da1d872c2fac13baffected · git
    • 7b54aaaf53cb784411426c64482af0435f7c845e and later · before 57f94d3f4dee8b54d63cefddf1112be4656ef9e6affected · git
    • 7b54aaaf53cb784411426c64482af0435f7c845e and later · before 50e5c6605cc9c2dd57bd2d1b3459674d19738983affected · git
    • before 5.15not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 6.1.187-16.1.187-1
Debian:12linux-6.12before 6.12.111-1~deb12u16.12.111-1~deb12u1
Debian:13linuxbefore 6.12.111-16.12.111-1
Debian:14linuxbefore 7.1.13-17.1.13-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-74705udp: fix potential use-after-free in tunnel segmentation
    40Plan
  • CVE-2026-74612veth: fix skb length accounting after XDP frag adjustment
    40Plan
  • CVE-2026-74475vxlan: use neigh_ha_snapshot() in route_shortcircuit()
    40Plan

Published before and after this one in the same product

  • ← EarlierCVE-2026-80840Sep 4, 2026 · ipv6: seg6: clear IPv4 control block on IPIP decapsulation
    0Monitor
  • ← EarlierCVE-2026-80841Sep 4, 2026 · net/packet: defer vmalloc TX_RING free until skbs finish
    0Monitor
  • Later →CVE-2026-80843Sep 4, 2026 · xfrm: fix xfrm_state_construct() auth-trunc leak
    0Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux22226a2c3b90f15b0925f1464470d3baa6c5677eVendor (CNA)
Linux Linux3a0ad4fcdfa0b7dba1876de14a12cb65c8b5ca50Vendor (CNA)
Linux Linux3afaaee2f972aec9059110953adb62fa3cf5c4bdVendor (CNA)
Linux Linux3f4752996735e0628af559aa8da1d872c2fac13bVendor (CNA)
Linux Linux50e5c6605cc9c2dd57bd2d1b3459674d19738983Vendor (CNA)
Linux Linux57f94d3f4dee8b54d63cefddf1112be4656ef9e6Vendor (CNA)
Linux Linux7c54fd8cfbcf371a5ef50db5c53fe6e85fb76686Vendor (CNA)
Linux Linuxc069f29da72324697aa4b7cab5b3647a7d24a575Vendor (CNA)
azl3 kernel 6.6.150.1-1 on Azure Linux 3.0—Microsoft (MSRC)
azl3 kernel 6.6.152.1-1 on Azure Linux 3.06.6.157.1-1 · Release NotesMicrosoft (MSRC)
debian:linux6.1.187-1 · Debian:12Package registry (OSV)
debian:linux-6.126.12.111-1~deb12u1 · Debian:12Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

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No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

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Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

No CVSS vector for this record, so attack conditions can't be derived.

Weakness class (CWE)

—

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

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References

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records