[CVE-2025-39964][MODERATE REGULAR] crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2025-39964
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg [ Upstream
Commit: 0f28c4adbc4a97437874c9b669fd7958a8c6d6ce
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0f28c4adbc4a97437874c9b669fd7958a8c6d6ce
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-39964
Analysis date: Wed, 23 Sep 2026 18:54:39 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2025-39964 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-39964

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 REGULAR
Manual review required: NO

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

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

CVE-2025-39964	MODERATE	https://www.kernelcve.org/list/?q=CVE-2025-39964 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;CWE-662;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A race in AF_ALG sendmsg allows two local threads to write to the same algorithm socket when the active write temporarily releases the socket lock while waiting for resources. Data from the writes can be interleaved and the shared AF_ALG operation state can become inconsistent, potentially producing incorrect operation behavior or an availability failure. For the CVSS the PR:L value is used because an unprivileged local process can normally create and use an AF_ALG socket but must execute local code and issue concurrent writes to its own socket. The issue is not network reachable because AF_ALG is a local kernel socket interface. The required race window supports AC:H. The available code does not establish a UAF, OOB access, information leak, or controlled write primitive, so privilege escalation is not currently supported and the grounded impact is denial of service.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) 	MAYBE	WRITE OOB INIT SIMPLEFIX LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Local unprivileged trigger. An ordinary local process can create an AF_ALG socket and issue concurrent sendmsg operations without host-admin-equivalent privilege.
* +0 Race penalty. Concurrent writes are repeatable and attacker-controlled, with no evidence of a narrow or externally uncontrollable timing window.
* +0 Reliable kernel crash. The commit establishes interleaved data and inconsistent socket state but does not establish an Oops, panic, or host-wide failure.
* +0 Weak corruption concern. The shared operation state can become inconsistent, but no invalid pointer, OOB access, stale object, lifetime violation, or concrete corruption sink is shown.
* +0 Strong exploitation leverage. Controlled reclaim, arbitrary write, callback influence, disclosure, and privilege escalation are not demonstrated.
* +0 Remote reachability. AF_ALG is a local kernel socket interface.
* No C or I signal is awarded because the affected state belongs to the callers own cryptographic socket and no cross-principal consequence is established.
* No extra paranoid point is awarded because stronger impact would require an unsupported memory-corruption or kernel-crash primitive.

3. Reachability analysis

An ordinary local process can create an AF_ALG socket and use multiple threads to issue writes against the same socket. No capability, namespace privilege, host administrator action, prior privileged runtime setup, or special hardware is required for the described sequence. AF_ALG must be compiled and the selected algorithm must be available, but this is not evidence of a rare or attacker-inaccessible configuration.

The attacker controls both concurrent operations, so attempts are inexpensive and repeatable. The patch does not establish that exploitation depends on a materially narrow race window. The interface is local-only and cannot be reached directly through network traffic.

4. Primitive and severity interpretation

The exact primitive is concurrent semantic interleaving of writes and inconsistent mutation of an active AF_ALG operation context. This is an invalid-state race, not a stale-object or memory-lifetime violation.

There is no concrete repeated release or refcount operation. No first operation ends an object lifetime, and no second operation mutates a potentially freed object. The patch establishes neither UAF nor OOB access nor controlled kernel corruption.

The appropriate classification is CLASS_C. The demonstrated consequence is unpredictable interleaving and potentially incorrect cryptographic operation state. A kernel crash is only speculative from the supplied evidence. There is no established leverage beyond disruption of the callers socket operation.

ImportantCandidate is NO because no Important-preserving primitive exists. AutoDowngradeAllowed is YES because the issue is an unprivileged but local invalid-state race without demonstrated memory corruption, boundary bypass, disclosure, host-wide DoS, or privilege escalation. Likely operational severity is Low-like to ordinary Moderate.

5. One-sentence report phrase

Concurrent writes to one AF_ALG socket can interleave data and leave the shared cryptographic operation state inconsistent, but the supplied evidence does not establish memory corruption, kernel crash, disclosure, or privilege escalation.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review the omitted wait and lock-release paths if confirmation is needed that inconsistent state cannot reach an invalid scatterlist or lifetime operation, but the current evidence does not justify preserving Important severity.

7. Call-site confidence

Call-site confidence: medium

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

Patch: crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg [ Upstream
Commit: 0f28c4adbc4a97437874c9b669fd7958a8c6d6ce
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0f28c4adbc4a97437874c9b669fd7958a8c6d6ce

Changed files:
  crypto/af_alg.c
  include/crypto/if_alg.h

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=0f28c4adbc4a97437874c9b669fd7958a8c6d6ce

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

The original Linux kernel CVE announcement for CVE-2025-39964 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-39964

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:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: unknown
  Paranoid ActionableScore: 1

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).