[CVE-2026-64551][MODERATE 7.0] sctp: validate STALE_COOKIE cause length before reading staleness

[CVE-2026-64551][MODERATE 7.0] sctp: validate STALE_COOKIE cause length before reading staleness

[AL-KERNEL]

CVE: CVE-2026-64551
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: sctp: validate STALE_COOKIE cause length before reading staleness
Commit: 6022da37786701df1fc5dd946a6dcba59d5473b1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6022da37786701df1fc5dd946a6dcba59d5473b1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64551
Analysis date: Wed, 29 Jul 2026 01:09:24 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A network reachable OOB read in SCTP STALE_COOKIE error handling can leak kernel memory by echoing a 4 byte out of bounds staleness value back to the peer, with no demonstrated write primitive or direct privilege escalation path.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-64551 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64551

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-64551	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N';CWE-125;*CWE-200;*CWE-20;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '7.5';DESCR 'An out of bounds read in SCTP STALE_COOKIE handling can occur when an ERROR chunk is processed in COOKIE_ECHOED state and the STALE_COOKIE cause is shorter than the 4 byte staleness field. The kernel can read past the cause and for a minimal ERROR chunk past skb tail, then echo the read value back to the peer in the Cookie Preservative field of the reply INIT. For the CVSS the PR:N is used because a network peer can trigger the path after driving the association into COOKIE_ECHOED without local code execution on the target. The issue is network reachable when SCTP is enabled and exposed to untrusted peers. Impact is information disclosure through a small kernel memory leak. No direct integrity impact is indicated because the primitive is an out of bounds read and echo of bytes, not a write or UAF.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) 	MAYBE	LEAK NETWORK SKB KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  A peer that can reach SCTP and drive an association into COOKIE_ECHOED can send the malformed ERROR chunk.

* Confidentiality impact plausible: +1
  The kernel reads past the STALE_COOKIE cause and echoes the value back in the Cookie Preservative field.

* Common networking protocol receive path: +1
  This is in SCTP packet/error handling, not a local-only control interface.

Paranoid additional interpretation:

* Local unprivileged trigger: +1
  The commit explicitly says the path is reachable by an unprivileged process using a raw SCTP socket in a user and network namespace.

Not applied:

* Generic memory corruption: +0
  This is an OOB read and disclosure path, not OOB write, UAF, double free, type confusion, or arbitrary write.

* Privilege escalation plausible: +0
  No write primitive, object lifetime abuse, or control-flow impact is shown.

* Reliable kernel crash / strong DoS: +0
  The described impact is memory disclosure through echoing stale data, not crash.

* Rare subsystem penalty: 0
  SCTP exposure is less common than TCP, but this is still a normal network protocol path and should not be auto-downgraded when exposed.

## 3. Reachability analysis

The bug is remotely reachable when SCTP is enabled and exposed to an attacker. The attacker needs to reach the SCTP endpoint and manipulate the association state into COOKIE_ECHOED, then send an ERROR chunk containing a malformed STALE_COOKIE cause with insufficient length.

Namespaces matter because the commit explicitly notes reachability by an unprivileged process using a raw SCTP socket in a user and network namespace. That supports PR:N for remote CVSS and supports local unprivileged concern for practical triage in namespace-enabled environments.

Realistic exploitation depends on SCTP being available and reachable. SCTP is not typically exposed on the public Internet as broadly as TCP services, but in telecom, signaling, clustered systems, or internal deployments it can be reachable by untrusted or semi-trusted peers.

Call-site confidence: high. The patch shows the caller walking error causes, the vulnerable callee reading the staleness value, and the fix passing the validated matched cause.

## 4. Severity interpretation

This behaves more like an actionable Moderate network information disclosure than ordinary Low or simple DoS. The primitive is a small OOB read, apparently 4 bytes per malformed cause handling event, with a direct network-visible echo path.

The realistic impact is kernel memory disclosure, not privilege escalation. The paranoid score is higher because the issue is network-triggerable and the leaked bytes may be repeated or useful for defeating mitigations, but the patch does not justify integrity impact or LPE scoring.

## 5. One-sentence report phrase

A network reachable OOB read in SCTP STALE_COOKIE error handling can leak kernel memory by echoing a 4 byte out of bounds staleness value back to the peer, with no demonstrated write primitive or direct privilege escalation path.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a network-reachable kernel OOB read with an explicit disclosure path back to the peer. Even though the leak appears small and no integrity primitive is shown, exposed SCTP deployments should not be auto-closed.

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: sctp: validate STALE_COOKIE cause length before reading staleness
Commit: 6022da37786701df1fc5dd946a6dcba59d5473b1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6022da37786701df1fc5dd946a6dcba59d5473b1

Commit description:

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.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Reported-by: Xiang Mei <xmei5@asu.edu>
Assisted-by: Claude:claude-opus-4-8
Cc: stable@vger.kernel.org
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Acked-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/20260704033545.2438373-2-bestswngs@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/sctp/sm_statefuns.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6022da37786701df1fc5dd946a6dcba59d5473b1

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-64551 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64551

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 7.5

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 4
  Paranoid ActionableScore: 5

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).