# CVE-2026-74739: net/sched: cls_u32: skip hash tables in u32_bind_class()

> A slab-out-of-bounds read in the Linux kernel's u32 classifier allows attackers to cause denial of service or leak memory information.

- **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:** 26 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-97740, BELL-CVE-2026-74739, DEBIAN-CVE-2026-74739, GHSA-phcw-98q8-79wf, UBUNTU-CVE-2026-74739

## What is CVE-2026-74739?

CVE-2026-74739 is a high-severity memory corruption 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: cls_u32: skip hash tables in u32_bind_class()

u32_walk() enumerates both struct tc_u_hnode and struct tc_u_knode
through the walker callback. u32_bind_class() unconditionally casts the
passed fh to tc_u_knode and accesses &n->res, so when fh is actually a
tc_u_hnode, which has no tcf_result member, this results in a
slab-out-of-bounds read of res->classid in tc_cls_bind_class().

The issue can be reproduced with the following commands:

    tc qdisc add dev lo root handle 1: hfsc
    tc class add dev lo parent 1: classid 1:1 hfsc sc rate 1000kbit
    tc filter add dev lo parent 1:1 protocol ip prio 1 u32 match u32 0 0 flowid 1:1
    tc class add dev lo parent 1: classid 1:2 hfsc sc rate 2000kbit

Fix this by skipping hash tables via the TC_U32_KEY(handle) check.

## Which versions are affected by CVE-2026-74739?


## How do I fix CVE-2026-74739?

Apply the vendor's patch.

## Is CVE-2026-74739 being exploited?

There is no known exploitation of CVE-2026-74739 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74739 and fix it if it is affected.

What it is: CVE-2026-74739 is a high-severity memory corruption 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-2026-74739 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-2026-74739/ (Markdown: https://insights.sbomify.com/CVE-2026-74739/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74739
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74739
- OSV: https://osv.dev/vulnerability/CVE-2026-74739

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74739/
Summaries are generated and may contain mistakes; the official description above is the record.