CVE-2026-80844

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.