CVE-2026-80842

CVE CVE-2026-80842EUVD EUVD-2026-71292Published 2026-09-04T15:54:52.000Z

What the advisory describes

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.

Source: EUVD (ENISA), in the words of the advisory.

Products the advisory names

These come from the advisory itself, not from any check we performed.

• Linux — Linux patch: 0; patch: 5.15.220; 7b54aaaf53cb784411426c64482af0435f7c845e <3afaaee2f972aec9059110953adb62fa3cf5c4bd; patch: 6.6.156; 7b54aaaf53cb784411426c64482af0435f7c845e <7c54fd8cfbcf371a5ef50db5c53fe6e85fb76686; patch: 6.18.49; 7b54aaaf53cb784411426c64482af0435f7c845e <3a0ad4fcdfa0b7dba1876de14a12cb65c8b5ca50; patch: 6.1.187; patch: 7.2.3; patch: 6.12.108; 5.15; 7b54aaaf53cb784411426c64482af0435f7c845e <c069f29da72324697aa4b7cab5b3647a7d24a575; 7b54aaaf53cb784411426c64482af0435f7c845e <50e5c6605cc9c2dd57bd2d1b3459674d19738983; 7b54aaaf53cb784411426c64482af0435f7c845e <3f4752996735e0628af559aa8da1d872c2fac13b; patch: 7.1.13; patch: 7.3-rc1; 7b54aaaf53cb784411426c64482af0435f7c845e <22226a2c3b90f15b0925f1464470d3baa6c5677e; 7b54aaaf53cb784411426c64482af0435f7c845e <57f94d3f4dee8b54d63cefddf1112be4656ef9e6

The versions shown are the advisory's own. Patchlage compares no version numbers and derives no judgement from them — which version is installed is something a person has to look up.

Carried in the product catalogue

An estate covering these products can be recorded in Patchlage. An advisory about them appears in the next morning's situation report.

• Linux — Linux

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