---
id: CVE-2026-72250
title: 'netfilter: nf_conntrack_reasm: guard mac_header adjustment after IPv6 defrag'
summary: |-
  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 th…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    6e8cd710ca35c576f5f2e5a396047c9ac61f75e5
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    2a95ec21824a8ad81ad660b12231456fc0ac9830
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    bbcdef2061b170af45702ce6b359c02c12acfc94
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    cd0d7bbc027b4d3329712cdcdeb4e5567ffd0d58
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    53ef70a315420ed31581d38343684b3bf9a3c76d
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    a58230f3a7c4f6c3261786bc1efb72c42e68cd25
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    00bdce2fda7e430d24cfbc96764a1b96deb31f82
  - >-
    Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 <
    3b08fed5b7e0d5e3a25d73ef3ba09cd33ade16c9
  - Linux 2.6.15
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-16T18:45:08.646891Z'
published: '2026-08-15'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T18:55:13.023Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-72250'
references:
  - url: 'https://git.kernel.org/stable/c/6e8cd710ca35c576f5f2e5a396047c9ac61f75e5'
  - url: 'https://git.kernel.org/stable/c/2a95ec21824a8ad81ad660b12231456fc0ac9830'
  - url: 'https://git.kernel.org/stable/c/bbcdef2061b170af45702ce6b359c02c12acfc94'
  - url: 'https://git.kernel.org/stable/c/cd0d7bbc027b4d3329712cdcdeb4e5567ffd0d58'
  - url: 'https://git.kernel.org/stable/c/53ef70a315420ed31581d38343684b3bf9a3c76d'
  - url: 'https://git.kernel.org/stable/c/a58230f3a7c4f6c3261786bc1efb72c42e68cd25'
  - url: 'https://git.kernel.org/stable/c/00bdce2fda7e430d24cfbc96764a1b96deb31f82'
  - url: 'https://git.kernel.org/stable/c/3b08fed5b7e0d5e3a25d73ef3ba09cd33ade16c9'
tags:
  - cve.org
epss: 0.00169
epssPercentile: 0.05793
ingestedAt: '2026-10-16T19:46:24.415Z'
---

## Overview

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.

## Affected

- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < 6e8cd710ca35c576f5f2e5a396047c9ac61f75e5`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < 2a95ec21824a8ad81ad660b12231456fc0ac9830`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < bbcdef2061b170af45702ce6b359c02c12acfc94`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < cd0d7bbc027b4d3329712cdcdeb4e5567ffd0d58`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < 53ef70a315420ed31581d38343684b3bf9a3c76d`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < a58230f3a7c4f6c3261786bc1efb72c42e68cd25`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < 00bdce2fda7e430d24cfbc96764a1b96deb31f82`
- `Linux >= 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1 < 3b08fed5b7e0d5e3a25d73ef3ba09cd33ade16c9`
- `Linux 2.6.15`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.