CVE-2026-72400 seg6: validate SRH length before reading fixed fields
A missing length check in the Linux kernel's SEG6 validation allows out-of-bounds reads via BPF, potentially causing a denial of service.
- 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-2026-72400?
CVE-2026-72400 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:
seg6: validate SRH length before reading fixed fields
seg6_validate_srh() reads fixed SRH fields such as srh->type and srh->hdrlen before checking that the supplied length covers the fixed struct ipv6_sr_hdr fields.
The BPF SEG6 encap path reaches this with a BPF program-supplied pointer and length: bpf_lwt_push_encap() and the SEG6 local BPF END_B6 and END_B6_ENCAP actions call bpf_push_seg6_encap(), which forwards the length to seg6_validate_srh() with no minimum-size guard. A 2-byte SEG6 encap header can therefore make the validator read srh->type at offset 2 beyond the caller-supplied buffer.
Reject lengths shorter than the fixed SRH at the top of seg6_validate_srh(), before any field is read. This fixes the BPF helper path and keeps the common validator robust.
Which versions are affected by CVE-2026-72400?
How do I fix CVE-2026-72400?
Apply the vendor's patch.
Is CVE-2026-72400 being exploited?
There is no known exploitation of CVE-2026-72400 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-72400, DEBIAN-CVE-2026-72400, GHSA-x2wv-639g-pv5q, UBUNTU-CVE-2026-72400.