CVE-2026-80844

Technical Description

In the Linux kernel, the following vulnerability has been resolved:

xfrm: ah6: validate routing header segments_left

AH6 rearranges routing-header addresses before computing or verifying the

ICV. ipv6_rearrange_rthdr() assumes that segments_left is not larger than

the number of addresses described by the routing header's hdrlen field.

That assumption does not hold for raw IPv6 HDRINCL packets. A packet with

hdrlen equal to 2 describes one address, but can carry an arbitrary

segments_left value. With segments_left equal to 255, the function moves

its address pointer 4,064 bytes backwards and passes a 4,064-byte length to

memmove(), resulting in an out-of-bounds access.

Validate the invariant locally before modifying the routing header or

performing any address-pointer arithmetic, and propagate malformed-header

errors to the existing AH6 input and output error paths.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References