CVE-2025-40297: 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] ...

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

Metrics

CVSS 3.1

7.8/10

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

0.19%

8.6th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= ec7328b59176227216c461601c6bd0e922232a9b, < e19085b2a86addccff33ab8536fc67ebd9d52198; >= ec7328b59176227216c461601c6bd0e922232a9b, < 3b60ce334c1ce8b3fad7e02dcd5ed9f6646477c8; >= ec7328b59176227216c461601c6bd0e922232a9b, < bf3843183bc3158e5821b46f330c438ae9bd6ddb; >= ec7328b59176227216c461601c6bd0e922232a9b, < 991fbe1680cd41a5f97c92cd3a3496315df36e4b; >= ec7328b59176227216c461601c6bd0e922232a9b, < 8dca36978aa80bab9d4da130c211db75c9e00048
Linux	Linux	5.18

References

Timeline

Published: Dec 8, 2025
Last Modified: Jul 30, 2026
Status: Deferred

Frequently Asked Questions

What is CVE-2025-40297?

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

How severe is CVE-2025-40297?

CVE-2025-40297 has a CVSS score of 7.8/10 (HIGH severity). The EPSS model estimates a 0.19% probability of exploitation in the next 30 days.

How do I fix CVE-2025-40297?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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