[CVE-2026-98289][LOW] af_unix: Unify scc_index when finalising SCC in __unix_walk_scc(). [ Upstream

[CVE-2026-98289][LOW] af_unix: Unify scc_index when finalising SCC in __unix_walk_scc(). [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98289
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: af_unix: Unify scc_index when finalising SCC in __unix_walk_scc(). [ Upstream
Commit: b8f71d69380a5fbc734c868acbeb560f1de1766f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b8f71d69380a5fbc734c868acbeb560f1de1766f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98289
Analysis date: Fri, 09 Oct 2026 02:47:34 -0400
ActionableScore: 3
ActionableScore lower bound: 2
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-2026-98289 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98289

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: LOW
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-2026-98289	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98289 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT LOW AEGIS_AS=2 LEGACY=LOW RESULT=SAME TEMP_MERGE=AEGIS_LOW_OVERRIDE (legacy and Aegis reconciliation agree; DECISION: both LOW)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-772;*CWE-401;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'An error in the AF_UNIX garbage collector can assign different scc_index values to vertices that belong to the same strongly connected component. With multiple back edges and a specific DFS order, unix_vertex_dead can treat part of the component as a reference to another component and leave the socket cycle uncollected. A local process can potentially repeat this pattern to retain socket buffers and file references passed through SCM_RIGHTS, causing resource consumption and possible denial of service. For the CVSS the PR:L value is used because a local unprivileged process can normally create AF_UNIX sockets and pass file descriptors, although practical impact depends on limits and repeatable accumulation. The issue is not network reachable because AF_UNIX is a local IPC mechanism. No UAF, out of bounds access, or premature free is supported by the changed code, so confidentiality and integrity remain unaffected.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 3)	MAYBE	REMOTE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH TEMP_AEGIS_LOW_OVERRIDE	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Conservative signals:

* +1 Local unprivileged trigger. An ordinary local process can create AF_UNIX sockets, construct descriptor cycles using SCM_RIGHTS, and influence graph traversal without host-admin privilege.
* +1 Concrete persistent kernel resource/reference leak. Incorrect SCC classification prevents `unix_collect_skb()` from collecting an otherwise dead cycle, retaining socket buffers and file references.
* Total: 2.

Paranoid additional signal:

* +1 Resource exhaustion consequence. Repeated construction of the affected graph can plausibly accumulate retained sockets, SKBs, and file references. This supports availability impact, although host-wide exhaustion and bypass of per-user limits are not demonstrated.
* Total: 3.

Important non-awarded signals:

* No heap or slab OOB write is present. The supplied B5-R retry-accumulated OOB profile does not apply.
* No UAF, premature free, double release, or stale post-lifetime dereference is established.
* No attacker-controlled overwrite, controlled reclaim, arbitrary write, or disclosure exists.
* No reliable kernel crash is demonstrated independently of possible long-term resource exhaustion.
* No confidentiality, integrity, authorization, or isolation-boundary impact is established.
* No remote-reachability point is awarded because AF_UNIX is local IPC.
* The DFS-order dependency is not treated as a hard timing race and receives no timing penalty.

3. Reachability analysis

The plausible attacker is an ordinary local user able to create AF_UNIX sockets and pass file descriptors with SCM_RIGHTS. Host-admin-equivalent privilege is not required for those operations.

No namespace capability is needed, so this is not a namespace-scoped privilege path. There is no special hardware, boot option, device assignment, or prior privileged setup indicated. The trigger depends on constructing an SCC with multiple back edges and arranging an affected DFS order, but it is a deterministic graph and traversal condition rather than a narrow concurrent race.

The attacker can instantiate the relevant sockets and graph. Repeatable host-wide accumulation remains less certain because normal descriptor, socket, memory, and inflight-FD limits may constrain practical exhaustion.

4. Primitive and severity interpretation

The exact defect is an SCC bookkeeping error in the AF_UNIX garbage collector. Vertices belonging to one SCC can retain different `scc_index` values, causing `unix_vertex_dead()` to interpret an internal edge as a reference from another SCC. The collector consequently fails to reclaim a dead socket cycle.

This is resource retention, not memory corruption. No object is accessed after its lifetime, and no second release or refcount mutation occurs through a dangling reference. The changed state is consumed only for garbage-collection eligibility and does not provide an attacker-useful structured corruption primitive.

PrimitiveClass is CLASS_C because the demonstrated security consequence is possible resource exhaustion through failure to collect dead cycles. ImportantCandidate is NO because neither a corruption primitive nor a security-boundary violation exists. AutoDowngradeAllowed is YES because unresolved Important-grade leverage is not present.

The likely operational severity is Low to ordinary Moderate. The paranoid score recognizes plausible sustained accumulation but does not promote the issue to Important.

5. One-sentence report phrase

An AF_UNIX SCC bookkeeping error can prevent cyclic SCM_RIGHTS socket references from being garbage collected, allowing a local unprivileged process to retain kernel resources and potentially cause denial of service through repeated accumulation.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a bounded bug class consisting of resource retention without UAF, OOB access, corruption, authorization bypass, or demonstrated host-wide exhaustion.

7. Call-site confidence

Call-site confidence: medium

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

Patch: af_unix: Unify scc_index when finalising SCC in __unix_walk_scc(). [ Upstream
Commit: b8f71d69380a5fbc734c868acbeb560f1de1766f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b8f71d69380a5fbc734c868acbeb560f1de1766f

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=b8f71d69380a5fbc734c868acbeb560f1de1766f

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

The original Linux kernel CVE announcement for CVE-2026-98289 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98289

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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 2
  Paranoid ActionableScore: 3

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).