CVE-2025-40297 net: bridge: fix use-after-free due to MST port state bypass
A use-after-free in the Linux kernel bridge module allows attackers to cause denial of service or execute code when MST and VLAN filtering are configured.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40297?
CVE-2025-40297 is a high-severity use after free vulnerability in Linux, published on 8 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
net: bridge: fix use-after-free due to MST port state bypass
syzbot reported[1] a use-after-free when deleting an expired fdb. It is due to a race condition between learning still happening and a port being deleted, after all its fdbs have been flushed. The port's state has been toggled to disabled so no learning should happen at that time, but if we have MST enabled, it will bypass the port's state, that together with VLAN filtering disabled can lead to fdb learning at a time when it shouldn't happen while the port is being deleted. VLAN filtering must be disabled because we flush the port VLANs when it's being deleted which will stop learning. This fix adds a check for the port's vlan group which is initialized to NULL when the port is getting deleted, that avoids the port state bypass. When MST is enabled there would be a minimal new overhead in the fast-path because the port's vlan group pointer is cache-hot.
[1] https://syzkaller.appspot.com/bug?extid=dd280197f0f7ab3917be
Which versions are affected by CVE-2025-40297?
How do I fix CVE-2025-40297?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2025-40297 being exploited?
There is no known exploitation of CVE-2025-40297 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40297, DEBIAN-CVE-2025-40297, GHSA-9jpf-8hq9-w5f5, ROOT-OS-DEBIAN-12-CVE-2025-40297, ROOT-OS-DEBIAN-13-CVE-2025-40297, ROOT-OS-UBUNTU-2404-CVE-2025-40297 and 1 more.