[CVE-2026-80521][MODERATE 7.0] af_unix: Unlink scc_entry in unix_del_edge(). [ Upstream

[CVE-2026-80521][MODERATE 7.0] af_unix: Unlink scc_entry in unix_del_edge(). [ Upstream

[AL-KERNEL]

CVE: CVE-2026-80521
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: af_unix: Unlink scc_entry in unix_del_edge(). [ Upstream
Commit: e3702470ced94fad74d71e2232f022d2eb752a6d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3702470ced94fad74d71e2232f022d2eb752a6d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80521
Analysis date: Wed, 26 Aug 2026 12:02:14 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-80521 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80521

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-2026-80521	MODERATE	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:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in AF_UNIX garbage collection can leave a stale scc_entry linked after part of a dead strongly connected component is freed. A local user can potentially trigger this through concurrent AF_UNIX socket send and close activity involving file descriptor passing, creating a timing window where a new edge is visible to GC before the skb is queued. A later GC pass may walk the stale SCC list entry and reach freed memory, making this a use after free candidate rather than a pure resource leak or warning. For the CVSS the PR:L is selected because reliable triggering requires local user or process execution, but no administrative privilege is normally needed to create AF_UNIX sockets. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality or integrity impact due to kernel use after free memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-80521 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	REMOTE UAF SKB KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4

1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

2. Signal breakdown

* Local unprivileged trigger: +1. AF_UNIX sockets and SCM file descriptor passing are normally reachable by local unprivileged users.
* Memory corruption, weak primitive: +1. The patch describes traversal through a stale `scc_entry` after partial SCC freeing, which is a UAF candidate, but no attacker-controlled reclaim or overwrite primitive is shown.
* Real lifetime corruption: +1. The bug is explicitly about an object/list lifetime mismatch where an SCC vertex can be freed while still reachable through `scc_entry`.
* Reliable kernel crash / strong DoS: +1. A later GC walk can dereference freed list state, making kernel crash or memory fault realistic.
* Broad/default/common subsystem: +1. AF_UNIX is a core local IPC subsystem commonly enabled and widely used.
* Hard or unreliable race / special timing required: -1. Triggering depends on a narrow race between `unix_add_edges()`, `skb_queue_tail()`, concurrent close, and GC.

Paranoid-only adjustment:

* Availability impact realistic: +1. In the paranoid score, the stale list traversal is treated as a host-wide crash risk rather than a minor local fault. This raises the score to 5 but stays within the race-UAF downgrade cap.

Not awarded:

* No remote/network trigger. AF_UNIX is local IPC, not remotely reachable.
* No strong LPE bonus. The patch does not show attacker-controlled reclaim, type confusion, callback dispatch, arbitrary write, or refcount takeover.
* No confidentiality or integrity impact in the conservative score. Those remain theoretical only.

3. Reachability analysis

A local user can potentially trigger the issue by creating AF_UNIX socket graphs with passed file descriptors and racing send and close operations so that GC observes an edge before the related skb is queued. No administrative privileges are normally required for basic AF_UNIX socket creation. User namespaces do not fundamentally change the main assessment because the relevant interface is already local-user reachable. The path is common and default-enabled, but exploitation is timing-sensitive and depends on GC behavior, so AC remains high.

4. Severity interpretation

This is stronger than an ordinary Moderate because it is a local unprivileged lifetime bug in a common kernel IPC subsystem with a concrete stale-list/UAF pattern. Realistic demonstrated impact is most likely local DoS via kernel crash. Theoretical privilege escalation cannot be excluded at triage time because UAF-class bugs sometimes become exploitable, but the patch does not show a strong reclaim or write primitive. Therefore the conservative score stays borderline at 4, while the paranoid score is 5 and should not be auto-closed.

5. One-sentence report phrase

A race in AF_UNIX garbage collection can leave a stale scc_entry reachable after partial SCC freeing, allowing a local unprivileged user to potentially trigger a use-after-free during later GC traversal and cause at least a kernel crash.

6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

Reason: this is a local unprivileged race-dependent UAF candidate in a broad default subsystem. The known evidence mainly supports DoS, but the lifetime corruption pattern is serious enough for manual review before downgrading or auto-closing.

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

Patch: af_unix: Unlink scc_entry in unix_del_edge(). [ Upstream
Commit: e3702470ced94fad74d71e2232f022d2eb752a6d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3702470ced94fad74d71e2232f022d2eb752a6d

Changed files:
  net/unix/garbage.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=e3702470ced94fad74d71e2232f022d2eb752a6d

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

The original Linux kernel CVE announcement for CVE-2026-80521 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80521

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