# CVE-2026-74740: net/sched: act_api: fix TOCTOU NULL deref on a->goto_chain

> A race condition in the Linux kernel traffic control API allows local attackers to trigger a NULL pointer dereference and cause a system crash.

- **Severity:** Not scored
- **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:** 26 Aug 2026
- **Updated:** 26 Aug 2026
- **Also known as:** AZL-97746, BELL-CVE-2026-74740, DEBIAN-CVE-2026-74740, UBUNTU-CVE-2026-74740

## What is CVE-2026-74740?

CVE-2026-74740 is a vulnerability in Linux, published on 26 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_api: fix TOCTOU NULL deref on a->goto_chain

tcf_action_exec() handles TC_ACT_GOTO_CHAIN by first checking
rcu_access_pointer(a->goto_chain) and then calling
tcf_action_goto_chain_exec(), which does a second, independent
rcu_dereference_bh(a->goto_chain) read and immediately dereferences
chain->filter_chain. A concurrent tcf_action_set_ctrlact() (e.g. the gact
replace path) can clear a->goto_chain between the two reads, so the second
read returns NULL and tcf_action_goto_chain_exec() dereferences NULL.

Fix the race by doing a single rcu_dereference_bh() read of a->goto_chain
in tcf_action_exec(), checking it once for NULL, and passing the resulting
chain pointer into tcf_action_goto_chain_exec(). This turns the split
check/use into a single check/use on one value.

## Which versions are affected by CVE-2026-74740?


## How do I fix CVE-2026-74740?

Apply the vendor's patch.

## Is CVE-2026-74740 being exploited?

There is no known exploitation of CVE-2026-74740 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74740 and fix it if it is affected.

What it is: CVE-2026-74740 is a vulnerability in Linux, published on 26 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-2026-74740 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-2026-74740/ (Markdown: https://insights.sbomify.com/CVE-2026-74740/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74740
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74740
- OSV: https://osv.dev/vulnerability/CVE-2026-74740

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74740/
Summaries are generated and may contain mistakes; the official description above is the record.