Improper locking in Linux kernel - CVE-2026-63988

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Main Vulnerability Database Vulnerabilities #VU138660

Improper locking in Linux kernel - CVE-2026-63988

Published: July 20, 2026


Vulnerability identifier: #VU138660
CSH Severity: Low
CVSS v4: 6.8 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-63988
CWE-ID: CWE-667
Exploitation vector: Local access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a local user to cause a denial of service.

The vulnerability exists due to improper lock management in brport_store() in the bridge sysfs interface when handling sysfs attribute writes that change bridge port flags and invoke dev_set_promiscuity(). A local user can write crafted values to affected bridge port sysfs attributes to cause a kernel BUG from sleeping in atomic context.

The issue affects non-STP bridge port attributes, while the STP-related path_cost and priority attributes are handled separately.


Affected software

Linux kernel
Ubuntu
linux-ibm (Ubuntu package)
linux-azure (Ubuntu package)
linux-aws (Ubuntu package)
linux-nvidia (Ubuntu package)
linux-nvidia-bos (Ubuntu package)

How to mitigate CVE-2026-63988

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
linux-ibm (Ubuntu package) - addressed in versions 7.0.0-1008.8, 7.0.0-1010.10
linux-azure (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1010.10
linux-aws (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1015.15
linux-nvidia (Ubuntu package) - addressed in versions 7.0.0-1016.16, 7.0.0-1016.16~24.04.1
linux-nvidia-bos (Ubuntu package) - update to 7.0.0-2016.16

External References

Related Security Bulletins