# CVE-2026-74663: net/sched: reject overly deep qdisc hierarchies

> Attackers can cause kernel stack exhaustion and denial of service by creating excessively deep qdisc hierarchies in the Linux kernel.

- **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:** 22 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-97095, BELL-CVE-2026-74663, DEBIAN-CVE-2026-74663, GHSA-qwcm-6g6c-27vm, UBUNTU-CVE-2026-74663

## What is CVE-2026-74663?

CVE-2026-74663 is a high-severity denial of service vulnerability in Linux, published on 22 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: reject overly deep qdisc hierarchies

Deep qdisc hierarchies can lead to excessive recursion in qdisc tree
walkers and exhaust the kernel stack. The existing loop check does not
cover the create-and-graft path, so a hierarchy can still be extended by
creating a new child qdisc below an already deep parent.

Store the hierarchy depth in struct Qdisc and update it when qdiscs are
grafted. Reject new child qdiscs once the parent is already at the maximum
allowed depth.

## Which versions are affected by CVE-2026-74663?


## How do I fix CVE-2026-74663?

Apply the vendor's patch.

## Is CVE-2026-74663 being exploited?

There is no known exploitation of CVE-2026-74663 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74663 and fix it if it is affected.

What it is: CVE-2026-74663 is a high-severity denial of service vulnerability in Linux, published on 22 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-2026-74663 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-2026-74663/ (Markdown: https://insights.sbomify.com/CVE-2026-74663/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74663
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74663
- OSV: https://osv.dev/vulnerability/CVE-2026-74663

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74663/
Summaries are generated and may contain mistakes; the official description above is the record.