# CVE-2026-64551: sctp: validate STALE_COOKIE cause length before reading staleness

> An attacker can leak uninitialized kernel memory by sending a malformed SCTP ERROR chunk, potentially exposing sensitive data.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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:** 27 Jul 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-94031, BELL-CVE-2026-64551, DEBIAN-CVE-2026-64551, GHSA-m58p-8fjh-3whj, OESA-2026-3986, ROOT-OS-DEBIAN-12-CVE-2026-64551, UBUNTU-CVE-2026-64551

## What is CVE-2026-64551?

CVE-2026-64551 is a critical vulnerability in Linux, published on 27 Jul 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:

sctp: validate STALE_COOKIE cause length before reading staleness

When an ERROR chunk with a STALE_COOKIE cause is received in the
COOKIE_ECHOED state, sctp_sf_do_5_2_6_stale() reads the 4-byte Measure
of Staleness that follows the cause header:

	err   = (struct sctp_errhdr *)(chunk->skb->data);
	stale = ntohl(*(__be32 *)((u8 *)err + sizeof(*err)));

err is the first cause in the chunk, not the STALE_COOKIE cause that
caused the dispatch, and nothing guarantees the staleness field is
present. sctp_walk_errors() only requires a cause to be as long as the
4-byte header, so for a STALE_COOKIE cause of length 4 the read runs
past the cause, and for a minimal ERROR chunk past skb->tail. The value
is echoed to the peer in the Cookie Preservative of the reply INIT,
leaking uninitialized memory.

sctp_sf_cookie_echoed_err() already walks to the STALE_COOKIE cause, so
check its length there and pass it to sctp_sf_do_5_2_6_stale(), which
reads that cause instead of the first one. A STALE_COOKIE cause too
short to hold the staleness field is discarded.

The read is reachable by any peer that can drive an association into
COOKIE_ECHOED, including an unprivileged process using a raw SCTP socket
in a user and network namespace.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-64551?


## How do I fix CVE-2026-64551?

Apply the vendor's patch.

## Is CVE-2026-64551 being exploited?

There is no known exploitation of CVE-2026-64551 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64551 and fix it if it is affected.

What it is: CVE-2026-64551 is a critical vulnerability in Linux, published on 27 Jul 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-2026-64551 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-2026-64551/ (Markdown: https://insights.sbomify.com/CVE-2026-64551/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64551
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64551
- OSV: https://osv.dev/vulnerability/CVE-2026-64551

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64551/
Summaries are generated and may contain mistakes; the official description above is the record.