Out-of-bounds write in Linux kernel - CVE-2026-63923

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Main Vulnerability Database Vulnerabilities #VU138728

Out-of-bounds write in Linux kernel - CVE-2026-63923

Published: July 20, 2026


Vulnerability identifier: #VU138728
CSH Severity: Low
CVSS v4: 6.9 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-63923
CWE-ID: CWE-787
Exploitation vector: Local access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a local user to cause a denial of service or overwrite out-of-bounds memory.

The vulnerability exists due to an out-of-bounds write in rvu_mbox_handler_rep_event_notify and the representor event handling path when processing a crafted REP_EVENT_NOTIFY mailbox request with a sender-controlled body pcifunc value. A local user can send a specially crafted mailbox request to cause a denial of service or overwrite out-of-bounds memory.

Exploitation requires a VF attached to a PF that has been put into switchdev representor mode. For RVU_EVENT_MAC_ADDR_CHANGE, the invalid body pcifunc is used as a six-byte ether_addr_copy() target in the queued worker.


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-2026-63923

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