CVE-2025-40297

net: bridge: fix use-after-free due to MST port state bypass

Published Dec 8, 2025 CVSS 3.1 · 7.8 High EPSS < 1% KEV · Not listed
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

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4436-1 linux-6.1 security update
Ubuntu USN Ubuntu USN USN-8028-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8029-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8030-1 Linux kernel (GCP) vulnerabilities
Ubuntu USN Ubuntu USN USN-8028-2 Linux kernel (Real-time) vulnerabilities
Ubuntu USN Ubuntu USN USN-8031-1 Linux kernel (GCP) vulnerabilities
Ubuntu USN Ubuntu USN USN-8029-2 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8028-3 Linux kernel (Real-time) vulnerabilities
Ubuntu USN Ubuntu USN USN-8028-4 Linux kernel (FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-8048-1 Linux kernel (OEM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8028-5 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8031-2 Linux kernel (GCP FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-8028-6 Linux kernel (HWE) vulnerabilities
Ubuntu USN Ubuntu USN USN-8031-3 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-8052-1 Linux kernel (Low Latency) vulnerabilities
Ubuntu USN Ubuntu USN USN-8028-7 Linux kernel (Low Latency NVIDIA) vulnerabilities
Ubuntu USN Ubuntu USN USN-8029-3 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-8028-8 Linux kernel (IBM) vulnerabilities
Ubuntu USN Ubuntu USN USN-8052-2 Linux kernel (Xilinx) vulnerabilities
Ubuntu USN Ubuntu USN USN-8074-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-8074-2 Linux kernel (Azure FIPS) vulnerabilities
Ubuntu USN Ubuntu USN USN-8126-1 Linux kernel (Azure) vulnerabilities
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}

cvssV3_1

{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'}

Type Values Removed Values Added
References
Metrics threat_severity

None

cvssV3_1

{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}

threat_severity

Moderate

Type Values Removed Values Added
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
Title net: bridge: fix use-after-free due to MST port state bypass
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References
Weaknesses

No weakness.

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
Oct 15, 2026, 10:02 PM
Reserved
Apr 16, 2025, 7:20 AM
Status
Deferred
Published
Dec 8, 2025, 1:16 AM
Modified
Oct 15, 2026, 10:19 PM
Severity
Moderate
Public date
Dec 8, 2025, 12:00 AM