Executive brief
A vulnerability in the Linux kernel's network bridging component could allow a local user to trigger system warnings or potential instability. The issue occurs when the system incorrectly tracks multicast group entries during specific network configuration changes. While primarily a technical inconsistency, it can lead to kernel warnings that may impact system reliability in specific networking environments.
Technical details
The vulnerability stems from a logic error in the net/bridge/br_multicast.c component where mdb_n_entries (the count of Multicast Database entries) is updated conditionally. Specifically, when a bridge port is down, certain multicast snooping enablement paths fail to increment the entry counter, but subsequent 'flush' operations attempt to decrement it. This results in an underflow or inconsistent state, triggering kernel warnings (br_multicast_port_ngroups_dec_one). An attacker with local administrative privileges or the ability to manipulate network interfaces could trigger this state. The fix ensures that the counter is always updated regardless of the current multicast options or interface state.
Affected products
- Linux Linux kernel 6.12 and earlier
Timeline
- 2026-02-13: patched: Initial patch submitted by Nikolay Aleksandrov
- 2026-05-27: disclosed: CVE-2026-45913 published
References
- https://git.kernel.org/stable/c/45525fdfd4cb612d7b414dd5cfa1f43892a7cd71
- https://git.kernel.org/stable/c/724a405ce0309676f1e993c173382b4c4a022beb
- https://git.kernel.org/stable/c/8b769e311a86bb9d15c5658ad283b86fc8f080a2
- https://git.kernel.org/stable/c/d0fdad1bdd21a358cc2c85da3681ae27b86ce6ce
- https://git.kernel.org/stable/c/fae260fc84e1eae8f590c7907e53e8768df2d986