# CVE-2026-64554: netfilter: bridge: fix stale prevhdr pointer in br_ip6_fragment()

> A use-after-free vulnerability in the Linux kernel bridge netfilter allows attackers to cause a kernel panic or potentially execute code via crafted IPv6 fragments.

- **Severity:** High 8.8 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Jul 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-94035, BELL-CVE-2026-64554, DEBIAN-CVE-2026-64554, GHSA-435j-q3ff-8922, ROOT-OS-DEBIAN-12-CVE-2026-64554, UBUNTU-CVE-2026-64554

## What is CVE-2026-64554?

CVE-2026-64554 is a high-severity use after free vulnerability in Linux, published on 27 Jul 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: bridge: fix stale prevhdr pointer in br_ip6_fragment()

br_ip6_fragment() gets prevhdr, a pointer into the skb head, from
ip6_find_1stfragopt(), then calls skb_checksum_help().  For a cloned skb
skb_checksum_help() reallocates the head via pskb_expand_head(), leaving
prevhdr dangling.  It is later dereferenced in ip6_frag_next(), causing a
use-after-free write.

Save prevhdr's offset before skb_checksum_help() and recompute it after,
like commit ef0efcd3bd3f ("ipv6: Fix dangling pointer when ipv6
fragment").

  BUG: KASAN: slab-use-after-free in ip6_frag_next (net/ipv6/ip6_output.c:857)
  Write of size 1 at addr ffff888013ff5016 by task exploit/141
  Call Trace:
   ...
   kasan_report (mm/kasan/report.c:595)
   ip6_frag_next (net/ipv6/ip6_output.c:857)
   br_ip6_fragment (net/ipv6/netfilter.c:212)
   nf_ct_bridge_post (net/bridge/netfilter/nf_conntrack_bridge.c:407)
   nf_hook_slow (net/netfilter/core.c:619)
   br_forward_finish (net/bridge/br_forward.c:66)
   __br_forward (net/bridge/br_forward.c:115)
   maybe_deliver (net/bridge/br_forward.c:191)
   br_flood (net/bridge/br_forward.c:245)
   br_handle_frame_finish (net/bridge/br_input.c:229)
   br_handle_frame (net/bridge/br_input.c:442)
   ...
   packet_sendmsg (net/packet/af_packet.c:3114)
   ...
   do_syscall_64 (arch/x86/entry/syscall_64.c:94)
   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
  Kernel panic - not syncing: Fatal exception in interrupt

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-64554?


## How do I fix CVE-2026-64554?

Apply the vendor's patch.

## Is CVE-2026-64554 being exploited?

There is no known exploitation of CVE-2026-64554 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64554 and fix it if it is affected.

What it is: CVE-2026-64554 is a high-severity use after free vulnerability in Linux, published on 27 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-64554 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-64554/ (Markdown: https://insights.sbomify.com/CVE-2026-64554/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64554
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64554
- OSV: https://osv.dev/vulnerability/CVE-2026-64554

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64554/
Summaries are generated and may contain mistakes; the official description above is the record.