# CVE-2026-72338: net/sched: act_pedit: fix TOCTOU heap OOB write in tc offload

> A race condition in the Linux kernel's traffic control allows local attackers with CAP_NET_ADMIN to trigger a heap out-of-bounds write, potentially leading to code execution or privilege escalation.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-72338, DEBIAN-CVE-2026-72338, GHSA-hgh2-wfvr-f9mp, UBUNTU-CVE-2026-72338

## What is CVE-2026-72338?

CVE-2026-72338 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:

net/sched: act_pedit: fix TOCTOU heap OOB write in tc offload

There is a TOCTOU race condition in flower lockless approach between sizing
a flow_rule buffer and filling it.
zdi-disclosures@trendmicro.com reports:
The cls_flower classifier operates with TCF_PROTO_OPS_DOIT_UNLOCKED
(fl_change runs without RTNL), while RTM_NEWACTION holds RTNL, so the
independent locking domains make the race reachable in practice.  KASAN
confirms:
  BUG: KASAN: slab-out-of-bounds in tcf_pedit_offload_act_setup+0x81b/0x930
  Write of size 4 at addr ffff888001f27520 by task poc-toctou/312
  The buggy address is located 0 bytes to the right of
   allocated 288-byte region [ffff888001f27400, ffff888001f27520)
   (cache kmalloc-512)

Note: The result is a heap OOB write attacker-controlled content into the
adjacent slab object (requires CAP_NET_ADMIN).

The fix introduces reading tcfp_nkeys under act->tcfa_lock in all places
using a new tcf_pedit_nkeys_locked() which replaces the old tcf_pedit_nkeys().
Additionally we close the remaining TOCTOU window between the sizing read and
the fill reads by more careful accounting.
Rather than silently truncating the key count, which leads to incorrect
action semantics offloaded to hardware and secondary OOB writes if
the remaining capacity is zero or consumed by prior actions, we enforce
remaining capacity checks and return -ENOSPC if the required space exceeds
the remaining capacity.

## Which versions are affected by CVE-2026-72338?


## How do I fix CVE-2026-72338?

Apply the vendor's patch.

## Is CVE-2026-72338 being exploited?

There is no known exploitation of CVE-2026-72338 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72338 and fix it if it is affected.

What it is: CVE-2026-72338 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.
Exploitation: There is no known exploitation of CVE-2026-72338 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-2026-72338/ (Markdown: https://insights.sbomify.com/CVE-2026-72338/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72338
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72338
- OSV: https://osv.dev/vulnerability/CVE-2026-72338

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72338/
Summaries are generated and may contain mistakes; the official description above is the record.