CVE-2026-72250 netfilter: nf_conntrack_reasm: guard mac_header adjustment after IPv6 defrag
A missing guard in Linux kernel IPv6 defragmentation causes an invalid MAC header offset, leading to potential kernel crashes or memory corruption.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72250?
CVE-2026-72250 is a high-severity vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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; mirror the guard here.
Which versions are affected by CVE-2026-72250?
How do I fix CVE-2026-72250?
Apply the vendor's patch.
Is CVE-2026-72250 being exploited?
There is no known exploitation of CVE-2026-72250 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-72250, DEBIAN-CVE-2026-72250, GHSA-9f37-2xqv-pf7f, UBUNTU-CVE-2026-72250.