[CVE-2026-98503][IMPORTANT] packet: use ubuf_info completion for TX_RING packets [ Upstream

[CVE-2026-98503][IMPORTANT] packet: use ubuf_info completion for TX_RING packets [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98503
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: packet: use ubuf_info completion for TX_RING packets [ Upstream
Commit: e67c455d79fbf709a94965f09a2be6bf4f4ba5fd
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e67c455d79fbf709a94965f09a2be6bf4f4ba5fd
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98503
Analysis date: Sat, 24 Oct 2026 03:11:04 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
AF_PACKET TX_RING slots could be returned to userspace or torn down while still referenced by an active skb, enabling payload aliasing and a plausible stale backing-page crash path.

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

The original Linux kernel CVE announcement for CVE-2026-98503 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98503

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.

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

CVE-2026-98503	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-98503 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, 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:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'TX_RING slots could be marked available when skb_orphan invoked the skb destructor even though skb fragments still referenced the slot payload. Userspace could then reuse or tear down aliased ring memory while the old skb remained active, causing packet data corruption and creating a plausible backing page use after free and kernel crash path. For the CVSS the PR:L value is selected because reliable triggering requires a local process able to create and operate an AF_PACKET TX_RING, commonly through CAP_NET_RAW or delegated namespace access. AC:H reflects the lifetime and timing conditions needed to reuse or remove the slot while references remain. The base impact is CIA:LLH because payload aliasing provides a concrete integrity effect and the teardown interaction may affect availability, while broader confidentiality or privilege escalation is not proven. The paranoid CIA:HHH score preserves the same lifetime violation class and accounts for the still defensible possibility that stale skb references reach freed ring backing pages. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to IMPORTANT because a specific evidence based protection or manual review veto was applied. final reconciliation stage IMPORTANT to IMPORTANT because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and V34_DOWNSTREAM_METADATA_KP_VETO and MANUAL_REVIEW_REQUIRED and V34_DOWNSTREAM_METADATA_DH_VETO and MANUAL_REVIEW_REQUIRED and TEMP_KPANIC_MERGE_IMPORTANT_WINS and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 3.6 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	INIT NOMEMCHK RACE UAF SKB TEST PACKET INCREASED_TO_HIGH_BASED_ON_GUESSCVSS V34_DOWNSTREAM_METADATA_KP_VETO MANUAL_REVIEW_REQUIRED V34_DOWNSTREAM_METADATA_DH_VETO MANUAL_REVIEW_REQUIRED TEMP_KPANIC_MERGE_IMPORTANT_WINS KPANIC_UNSUPPORTED_REMOVED	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3.
* Conservative score: 5. REAL UAF FLOOR 5 raises 3 -> 5 because userspace can reuse an explicitly released TX_RING slot while its payload remains referenced and actively consumed by an skb.
* Raw paranoid score: 3.
* Paranoid score: 5. No additional speculative reclaimed-page or LPE point.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 real lifetime violation/UAF: `skb_orphan()` invoked the old destructor, marking the slot available while skb fragments still referenced its payload. The added `sk_wmem_alloc` lifetime hold also prevents ring-page freeing before those references finish.
* +1 attacker-influenced lifetime/reuse: the TX_RING user can observe the slot as available and rewrite or tear down it while the old skb remains active.
* +1 plausible kernel crash/strong DoS: premature ring backing release can leave skb fragments referencing pages whose required lifetime ended.
* -1 reduced privilege: AF_PACKET creation requires CAP_NET_RAW, but that is narrower than host-administrator-equivalent power and may be delegated.
* No hard-race penalty: timing is involved, but the patch does not establish a narrow, one-shot, externally uncontrollable race.
* No strong-leverage, confidentiality, or protected-integrity points: controlled reclaim, arbitrary kernel write, sensitive adjacent victim, disclosure, and LPE are not shown.
* This is not NEW52 B5-R, NEW53 B3-PENDING, or an authorization/B4 case.

3. Reachability analysis

A local process able to create and operate an AF_PACKET TX_RING can transmit packets and reuse slots after the vulnerable destructor reports them available. This does not require host UID 0; CAP_NET_RAW can be delegated. Namespace-local CAP_NET_RAW is credible, but the supplied evidence does not fully prove that every setup and trigger stage is available in an attacker-created user/net namespace, so `NamespaceScopedPrivilege=UNKNOWN`. No special hardware is required.

4. Primitive and severity reading

The primitive is premature release of user-mapped ring-slot ownership while an active skb retains fragment references. It is more than a shallow cleanup dereference: attacker-rewritten payload is later consumed by networking, and teardown can end backing-page lifetime prematurely. This is CLASS_B, not CLASS_A, because no controlled kernel-object reclaim, directed kernel overwrite, or privilege escalation is demonstrated. The concrete active lifetime and aliasing primitive makes Important-vs-Moderate leverage unresolved, so automatic downgrade is unsafe.

5. One-sentence report phrase

AF_PACKET TX_RING slots could be returned to userspace or torn down while still referenced by an active skb, enabling payload aliasing and a plausible stale backing-page crash path.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm namespace reachability, ring teardown behavior, and whether stale fragments can reach reused kernel-owned pages beyond packet-payload corruption.

7. Call-site confidence

Call-site confidence: high

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

Patch: packet: use ubuf_info completion for TX_RING packets [ Upstream
Commit: e67c455d79fbf709a94965f09a2be6bf4f4ba5fd
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e67c455d79fbf709a94965f09a2be6bf4f4ba5fd

Changed files:
  include/linux/skbuff.h
  net/packet/af_packet.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=e67c455d79fbf709a94965f09a2be6bf4f4ba5fd

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

The original Linux kernel CVE announcement for CVE-2026-98503 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98503

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:L/I:L/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: unknown
  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: IMPORTANT
KPANIC detected for this report: NO
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).