Linux Kernel Bridge: UAF via multicast snooping toggle
CVE-2026-64032 Published on July 19, 2026
bridge: mcast: Fix a possible use-after-free when removing a bridge port
In the Linux kernel, the following vulnerability has been resolved:
bridge: mcast: Fix a possible use-after-free when removing a bridge port
When per-VLAN multicast snooping is enabled, the bridge iterates over
all the bridge ports, disables the per-port multicast context on each
port and enables the per-{port, VLAN} multicast contexts instead. The
reverse happens when per-VLAN multicast snooping is disabled.
When global multicast snooping is enabled, the bridge iterates over all
the bridge ports and enables the per-port multicast context on each
port. The reverse happens when multicast snooping is disabled.
The above scheme can result in a situation where both types of contexts
(per-port and per-{port, VLAN}) are enabled on a single bridge port:
# ip link add name br1 up type bridge mcast_snooping 1 mcast_querier 1 vlan_filtering 1
# ip link add name dummy1 up master br1 type dummy
# ip link set dev br1 type bridge mcast_vlan_snooping 1
# ip link set dev br1 type bridge mcast_snooping 0
# ip link set dev br1 type bridge mcast_snooping 1
This is not intended and it is a problem since the commit cited below.
Prior to this commit, when removing a bridge port,
br_multicast_disable_port() would disable the per-port multicast context
and the per-{port, VLAN} multicast contexts would get disabled when
flushing VLANs.
After this commit, br_multicast_disable_port() only disables the
per-port multicast context if per-VLAN multicast snooping is disabled.
If both types of contexts were enabled on the port when it was removed,
the per-port multicast context would remain enabled when freeing the
bridge port, leading to a use-after-free [1].
Fix by preventing the bridge from enabling / disabling the per-port
multicast contexts when toggling global multicast snooping if per-VLAN
multicast snooping is enabled.
[1]
ODEBUG: free active (active state 0) object: ffff88810f8bda78 object type: timer_list hint: br_ip6_multicast_port_query_expired (net/bridge/br_multicast.c:1927)
WARNING: lib/debugobjects.c:629 at debug_print_object+0x1b1/0x3e0, CPU#5: swapper/5/0
[...]
Call Trace:
<IRQ>
__debug_check_no_obj_freed (lib/debugobjects.c:1116)
kfree (mm/slub.c:2620 mm/slub.c:6250 mm/slub.c:6565)
kobject_cleanup (lib/kobject.c:689)
rcu_do_batch (kernel/rcu/tree.c:2617)
rcu_core (kernel/rcu/tree.c:2869)
handle_softirqs (kernel/softirq.c:622)
__irq_exit_rcu (kernel/softirq.c:656 kernel/softirq.c:496 kernel/softirq.c:735)
irq_exit_rcu (kernel/softirq.c:752)
sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1061 (discriminator 47) arch/x86/kernel/apic/apic.c:1061 (discriminator 47))
</IRQ>
Products Associated with CVE-2026-64032
stack.watch emails you whenever new vulnerabilities are published in Linux Kernel or Canonical Ubuntu Linux. Just hit a watch button to start following.
Affected Versions
Linux:- Version 410a033bfa8c7daefbae0225c836693db2149ec1 and below ddefd1b8e5eb58933a697ab38334f0fd82e7fb8b is affected.
- Version c6d16eab122744df698f18b47cf771945cd55066 and below ed3b69e60385a03df11c6d12e5d7bdf0f4a11b70 is affected.
- Version b4c83b37490d61cfdd62a2b29e98a9b89004b5c0 and below 1900ca8acb92fbea8bf9abef9927c7fed03db7fc is affected.
- Version 78f768e36c065ca3f88272fcf39014782c2d4ecd and below ebe5561154c823b323bd06e350b55e0b8604d851 is affected.
- Version 4b30ae9adb047dd0a7982975ec3933c529537026 and below a9224862d597d0eed0a34bbb27343f703fc4113f is affected.
- Version 4b30ae9adb047dd0a7982975ec3933c529537026 and below 7213256c91ed778a0997c2029c152b18dc50e4fd is affected.
- Version 4b30ae9adb047dd0a7982975ec3933c529537026 and below 4df78ff02629c7729168f0696a7a2123c389818d is affected.
- Version c996e25df0b3282c724bb5aca434518bc08cd963 is affected.
- Version 5.15.186 and below 5.15.209 is affected.
- Version 6.1.142 and below 6.1.175 is affected.
- Version 6.6.95 and below 6.6.142 is affected.
- Version 6.12.35 and below 6.12.92 is affected.
- Version 6.15.4 and below 6.16 is affected.
- Version 6.16 is affected.
- Before 6.16 is unaffected.
- Version 5.15.209, <= 5.15.* is unaffected.
- Version 6.1.175, <= 6.1.* is unaffected.
- Version 6.6.142, <= 6.6.* is unaffected.
- Version 6.12.92, <= 6.12.* is unaffected.
- Version 6.18.34, <= 6.18.* is unaffected.
- Version 7.0.11, <= 7.0.* is unaffected.
- Version 7.1, <= * is unaffected.