[CVE-2026-98631][MODERATE REGULAR] xsk: Use a 32-bit compare in xsk_map_gen_lookup [ Upstream

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

CVE: CVE-2026-98631
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: xsk: Use a 32-bit compare in xsk_map_gen_lookup [ Upstream
Commit: c6d5c582d55a8f229d75e98d62eaa065b0deb18d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6d5c582d55a8f229d75e98d62eaa065b0deb18d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98631
Analysis date: Sat, 24 Oct 2026 12:24:23 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A signed-width error in generated XSKMAP lookup code permits an extreme-size map index to read beyond the pointer array and potentially use adjacent data as an `xsk_sock` pointer.

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

The original Linux kernel CVE announcement for CVE-2026-98631 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98631

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: YES

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

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

CVE-2026-98631	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98631 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-125;CWE-194;CWE-681;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A generated XSKMAP lookup used a 64 bit BPF immediate comparison for a 32 bit key. When max_entries is at least 0x80000000, sign extension makes the comparison threshold larger than every zero extended key, allowing an out of range index to reach an out of bounds pointer load from xsk_map. The confirmed primitive is an out of bounds read of a value later treated as an xsk_sock pointer, with a plausible kernel crash if the invalid pointer is used. Limited confidentiality or integrity impact remains possible but unproven because the loaded value may cross a kernel object boundary, while no controlled write or direct information disclosure is demonstrated. For the CVSS the PR:L value reflects that reliable triggering requires a local user or service context able to create a very large XSKMAP and load or use the relevant BPF program. AC:H reflects the extreme map size and substantial memory requirement. Remote packet influence alone does not establish remote reachability. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.8 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the manual review requirement was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.1 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	OOB BPF SIMPLEFIX IMPROVEONLY LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; no floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +1 weak/indirect corruption candidate: the signed 64-bit immediate comparison can admit a zero-extended out-of-range index, causing a confirmed read beyond `xsk_map[]`.
* +1 plausible kernel crash: the loaded out-of-bounds word is treated as an `xsk_sock` pointer, so later use can fault.
* Paranoid +1 unsafe active-object selection: cross-object bytes may become a kernel object pointer consumed by generated lookup users. The exact dereference and any useful non-crash effect are not shown.
* No privilege penalty: host-admin-equivalent privilege is not positively established.
* No confidentiality, integrity, disclosure, write, controlled target, reclaim, or LPE points.
* No extra availability point; it would duplicate the same possible crash.
* NEW52/B5-R does not apply: there is no retry-accumulated OOB write.
* NEW53/B3-PENDING and NEW54/B4-PENDING do not apply.

3. Reachability analysis

Triggering requires creation of an XSKMAP with `max_entries >= 0x80000000` and execution of the generated BPF lookup. This implies extreme allocation pressure and likely configuration or BPF privilege constraints, but the supplied patch does not establish the complete capability checks, namespace scope, or below-host-admin path. Remote packets alone do not establish reachability. No timing race or special hardware is required.

4. Primitive and severity reading

The proven primitive is a heap/slab-adjacent OOB pointer read caused by a 64-bit sign-extension mismatch. It is not a UAF or write. The downstream value is interpreted as an active `xsk_sock` pointer, but the supplied code does not show a controlled dereference, disclosure, callback, or state mutation. This supports CLASS_C and plausible DoS, not an Important-grade corruption primitive. ImportantCandidate is therefore NO; downgrade remains allowed after the required reachability and consumer review.

5. One-sentence report phrase

A signed-width error in generated XSKMAP lookup code permits an extreme-size map index to read beyond the pointer array and potentially use adjacent data as an `xsk_sock` pointer.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm BPF/XSK privilege scope, feasibility of the very large allocation, and the first downstream consumer of the invalid pointer.

7. Call-site confidence

Call-site confidence: medium

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

Patch: xsk: Use a 32-bit compare in xsk_map_gen_lookup [ Upstream
Commit: c6d5c582d55a8f229d75e98d62eaa065b0deb18d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6d5c582d55a8f229d75e98d62eaa065b0deb18d

Changed files:
  net/xdp/xskmap.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=c6d5c582d55a8f229d75e98d62eaa065b0deb18d

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

The original Linux kernel CVE announcement for CVE-2026-98631 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98631

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:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 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).