# CVE-2026-72057: net/sched: act_ct: preserve tc_skb_cb across defragmentation

> Attackers can cause a kernel panic in Linux systems with panic_on_warn enabled by sending fragmented traffic through the act_ct module.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-72057, DEBIAN-CVE-2026-72057, GHSA-r6mf-v83v-v392, UBUNTU-CVE-2026-72057

## What is CVE-2026-72057?

CVE-2026-72057 is a high-severity denial of service vulnerability in Linux, published on 15 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

net/sched: act_ct: preserve tc_skb_cb across defragmentation

tcf_ct_handle_fragments() calls nf_ct_handle_fragments() without saving
and restoring skb->cb. The defrag helper clears IPCB/IP6CB, which aliases
the tc_skb_cb/qdisc_skb_cb control buffer. Fragmented traffic through
act_ct therefore loses qdisc metadata such as pkt_segs and can trigger
WARN_ON_ONCE() in qdisc_pkt_segs() when panic_on_warn is enabled.

Save and restore the full tc_skb_cb around nf_ct_handle_fragments(),
matching the pattern used by ovs_ct_handle_fragments().

Weakness: CWE-662 (Improper Synchronization)

## Which versions are affected by CVE-2026-72057?


## How do I fix CVE-2026-72057?

Apply the vendor's patch.

## Is CVE-2026-72057 being exploited?

There is no known exploitation of CVE-2026-72057 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72057 and fix it if it is affected.

What it is: CVE-2026-72057 is a high-severity denial of service vulnerability in Linux, published on 15 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-72057 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-2026-72057/ (Markdown: https://insights.sbomify.com/CVE-2026-72057/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72057
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72057
- OSV: https://osv.dev/vulnerability/CVE-2026-72057

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72057/
Summaries are generated and may contain mistakes; the official description above is the record.