CVE-2025-40363 net: ipv6: fix field-spanning memcpy warning in AH output
A memory corruption issue in the Linux kernel IPv6 AH output path can cause a kernel warning and potential denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40363?
CVE-2025-40363 is a memory corruption vulnerability in Linux, published on 16 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
net: ipv6: fix field-spanning memcpy warning in AH output
Fix field-spanning memcpy warnings in ah6_output() and ah6_output_done() where extension headers are copied to/from IPv6 address fields, triggering fortify-string warnings about writes beyond the 16-byte address fields.
memcpy: detected field-spanning write (size 40) of single field "&top_iph->saddr" at net/ipv6/ah6.c:439 (size 16) WARNING: CPU: 0 PID: 8838 at net/ipv6/ah6.c:439 ah6_output+0xe7e/0x14e0 net/ipv6/ah6.c:439
The warnings are false positives as the extension headers are intentionally placed after the IPv6 header in memory. Fix by properly copying addresses and extension headers separately, and introduce helper functions to avoid code duplication.
Which versions are affected by CVE-2025-40363?
How do I fix CVE-2025-40363?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2025-40363 being exploited?
There is no known exploitation of CVE-2025-40363 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40363, DEBIAN-CVE-2025-40363, GHSA-9gfg-vfjm-p94q, ROOT-OS-DEBIAN-12-CVE-2025-40363, ROOT-OS-DEBIAN-13-CVE-2025-40363, ROOT-OS-UBUNTU-2204-CVE-2025-40363 and 2 more.