CVE-2026-72250

Technical Description

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

netfilter: nf_conntrack_reasm: guard mac_header adjustment after IPv6 defrag

nf_ct_frag6_reasm() slides the packet head forward to drop the IPv6

fragment header and then unconditionally advances skb->mac_header:

skb->mac_header += sizeof(struct frag_hdr);

On the NF_INET_LOCAL_OUT defrag path the skb has no link-layer header

yet, so skb->mac_header is still the "not set" sentinel (u16)~0U. Adding

sizeof(struct frag_hdr) wraps it to a small value (0xffff + 8 == 7),

after which skb_mac_header_was_set() wrongly reports a MAC header is

present and skb_mac_header() points into the headroom.

The reassembler has done this unconditional add since it was introduced;

it was harmless while mac_header was a bare pointer, but wrong once

mac_header became a u16 offset whose unset state is the ~0U sentinel

tested by skb_mac_header_was_set(). The sibling net/ipv6/reassembly.c

does the same relocation and does guard the adjustment

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