[CVE-2026-52924][IMPORTANT] sctp: purge outqueue on stale COOKIE-ECHO handling [ Upstream

[CVE-2026-52924][IMPORTANT] sctp: purge outqueue on stale COOKIE-ECHO handling [ Upstream

[AL-KERNEL]

CVE: CVE-2026-52924
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: sctp: purge outqueue on stale COOKIE-ECHO handling [ Upstream
Commit: 84b7a319105db2f917ccdcf502bdc866082b1285
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=84b7a319105db2f917ccdcf502bdc866082b1285
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52924
Analysis date: Wed, 24 Jun 2026 05:05:24 -0400
ActionableScore: 8
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A remote SCTP peer may trigger stale COOKIE-ECHO handling that leaves scheduler state pointing to freed stream data, causing a use-after-free in SCTP dequeue paths and at least a kernel crash, with worst-case memory-corruption impact requiring manual review.

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

The original Linux kernel CVE announcement for CVE-2026-52924 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52924

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: IMPORTANT
Manual review required: YES

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

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

CVE-2026-52924	IMPORTANT	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-664;CWE-703;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.1';DESCR 'A use after free can occur in the SCTP stale COOKIE-ECHO handling path when a Stale Cookie ERROR rolls an association back from COOKIE_ECHOED to COOKIE_WAIT while user data is already queued or bundled with COOKIE-ECHO. The stream update path can free the old stream state, while scheduler cached state such as stream out_curr or queued transmit state can still reference the freed sctp_stream_out entry. Later SCTP dequeue paths such as FCFS, RR, or PRIO may dereference the stale stream state and crash the kernel. For the CVSS the PR:N is used because a remote SCTP peer can influence this protocol state through network packets when SCTP is exposed, without requiring privileges on the victim host. The issue is network reachable but AC:H is used because the trigger depends on a specific association setup and stale cookie rollback sequence. Impact is at least remote denial of service. For the paranoid score, the highest still-defensible interpretation is used because the bug is a real use after free in kernel networking code, so confidentiality and integrity impact may be possible in worst case and the issue should not be auto closed without manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	READ DANGER UAF NETWORK KERNEL_PANIC_PLUS_UAF HARDWARE LINUS KPANIC 	NO	NO	checked

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

ActionableScore=8
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  SCTP packet processing can be influenced by a remote SCTP peer if SCTP is exposed.
* Memory corruption, strong corruption primitive: +2
  The commit explicitly describes a slab-use-after-free involving `stream->out_curr` pointing to a freed `sctp_stream_out`.
* Real lifetime corruption: +1
  Old stream state is freed by `sctp_stream_free()`, while scheduler state can retain stale references.
* Reliable kernel crash / strong DoS: +1
  KASAN reports a concrete UAF crash in `sctp_sched_fcfs_dequeue()`.
* Hard or unreliable state sequence: -1
  Trigger requires a specific SCTP association rollback path involving stale COOKIE-ECHO handling and queued or bundled user data.

Conservative total: 5

Paranoid additional signals:

* Weak LPE concern: +1
  This is not just a NULL dereference. It is stale object reuse after free in kernel networking scheduler state, although no controlled reclaim or write primitive is demonstrated.
* Confidentiality impact plausible: +1
  In worst case, UAF reuse in kernel heap objects can expose stale or misinterpreted data, but this is not demonstrated.
* Integrity impact plausible: +1
  In worst case, stale object reuse may corrupt scheduler state or adjacent protocol state, but no arbitrary write is shown.

Paranoid total: 8

Not counted:

* No broad/default exposure bonus. SCTP is a real network protocol but is not commonly exposed on public interfaces by default.
* No Dirty-Pipe-like or page-cache primitive.
* No strong LPE bonus because the patch does not show attacker-controlled reclaim, overwrite, callback dispatch, refcount takeover, or arbitrary write.

## 3. Reachability analysis

A remote SCTP peer can plausibly trigger the vulnerable state machine path if SCTP is enabled and reachable. The bug is in the SCTP receive/state handling path, not in a local-only ioctl or admin-only control plane. No local privileges on the victim are required for the network interpretation.

The realistic trigger is not trivial. It requires a stale COOKIE-ECHO error rollback from `COOKIE_ECHOED` to `COOKIE_WAIT` while outbound data has already been queued or bundled, leaving scheduler state referencing old stream objects. This supports high attack complexity, but not an admin-only privilege requirement.

Namespaces do not materially reduce the network-facing risk if the SCTP endpoint is exposed. In local/container scenarios, the risk depends on whether untrusted code can create SCTP sockets or reach a host SCTP listener.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is a real UAF in a network protocol receive path with a demonstrated kernel crash. The conservative behavior is remote DoS with high complexity, which lands in Actionable Moderate territory.

The Important-class concern comes from the UAF lifetime primitive in kernel networking code. There is no demonstrated privilege escalation primitive, controlled reclaim, or arbitrary write, so the realistic evidence remains DoS. However, the paranoid score should not auto-close it because stale object reuse after free in a remotely reachable protocol path can sometimes be underestimated during early triage.

## 5. One-sentence report phrase

A remote SCTP peer may trigger stale COOKIE-ECHO handling that leaves scheduler state pointing to freed stream data, causing a use-after-free in SCTP dequeue paths and at least a kernel crash, with worst-case memory-corruption impact requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a remotely reachable SCTP UAF with demonstrated kernel crash and plausible worst-case memory-corruption implications, even though practical privilege escalation is not demonstrated by the patch.

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

Patch: sctp: purge outqueue on stale COOKIE-ECHO handling [ Upstream
Commit: 84b7a319105db2f917ccdcf502bdc866082b1285
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=84b7a319105db2f917ccdcf502bdc866082b1285

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=84b7a319105db2f917ccdcf502bdc866082b1285

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

The original Linux kernel CVE announcement for CVE-2026-52924 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52924

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:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 5
  Paranoid ActionableScore: 8

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).