[CVE-2026-98589][MODERATE 7.0] bpf: Reject pkt arguments in mutating subprogs [ Upstream

[CVE-2026-98589][MODERATE 7.0] bpf: Reject pkt arguments in mutating subprogs [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98589
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Reject pkt arguments in mutating subprogs [ Upstream
Commit: 0b6b2bb9b90ad1e2d94d18f626258a1dbbdee0ea
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b6b2bb9b90ad1e2d94d18f626258a1dbbdee0ea
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98589
Analysis date: Fri, 23 Oct 2026 20:14:38 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A BPF verifier type mismatch can preserve a packet pointer after a mutating subprogram invalidates its backing memory, permitting verifier-approved stale reads or writes with kernel crash and unresolved privilege-escalation potential.

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

The original Linux kernel CVE announcement for CVE-2026-98589 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98589

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.

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

CVE-2026-98589	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98589 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-119;CWE-693;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'The BPF verifier represents a PTR_TO_PACKET argument as PTR_TO_MEM when it is passed to a global subprogram. If that subprogram invokes a pskb helper that changes or reallocates packet data, the verifier may continue to treat the previous pointer and its bounds as valid even though the underlying packet memory has been invalidated. A later BPF access can therefore use stale packet memory and may result in an out of bounds access or a use after free condition in kernel context. For the CVSS the PR:L value is selected because exploitation requires local ability to load and execute a suitable BPF program, but delegated BPF or network capabilities may provide this access without full administrative control. The issue is not directly network reachable. Impact is at least a local denial of service via kernel crash and in the worst case may allow kernel memory disclosure, memory corruption, privilege escalation, or container escape. The verifier bypass and possible stale pointer primitive require manual security review. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7.8 and the production ActionableScore returned 6 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 LOW to MODERATE_KPANIC because the manual review requirement was applied. ActionableScore thresholds stage MODERATE_KPANIC to IMPORTANT because the ActionableScore threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC 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 has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK and INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP. The independent weaker Aegis shadow evaluated CVSS 4.3 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	MAYBE	BPF SIMPLEFIX LINUS PACKET  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

## 1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* No floor or cap changed either score. The BPF privileged-control-plane cap of 5 conservative and 6 paranoid is satisfied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

## 2. Signal breakdown

Conservative signals:

* +2 Real UAF or equivalent lifetime violation. A packet pointer can remain usable as `PTR_TO_MEM` after a `pskb_*` operation invalidates or reallocates its backing packet memory.
* +1 Attacker-influenced lifetime sequence. The submitted BPF program selects the mutating subprogram and can subsequently use the incorrectly preserved pointer.
* +1 Meaningful weak exploitation leverage. The BPF program can perform a verifier-approved read or write through stale packet memory, rather than merely causing a fixed cleanup dereference.
* +1 Realistic kernel crash or strong DoS from accessing invalid packet backing memory.
* Total: 5.

Paranoid difference:

* The +1 weak-leverage signal becomes +2 strong unresolved leverage. An attacker-authored BPF program can select the stale access offset, operation, and written value within verifier-approved bounds after the original backing memory has been invalidated. Controlled reclaim and an arbitrary target are not established, so this remains Class B rather than Class A.
* Total: 6.

Not awarded:

* No remote-reachability bonus. Network traffic alone does not load the required BPF program.
* No local-unprivileged bonus. Complete unprivileged BPF loading and attachment are not established.
* No confidentiality or integrity bonus. Read-back of protected data and corruption of a specific protected object are not demonstrated.
* No extra availability point. The possible crash is counted once.
* No controlled-reclaim, arbitrary-write, callback-control, or demonstrated LPE bonus.
* No repeated-release/refcount signal. There is no first release followed by a second lifetime mutation on the same reference.
* No B5-R retry-accumulated OOB classification. Neither retry accumulation nor a confirmed retry-driven heap OOB write is shown.
* No B3-PENDING shared-backing classification.
* No V32, V33, or V34 checksum-metadata chain is present.
* No B4 authorization profile. The new verifier rejection is memory-safety validation, not an authorization DENY-to-ALLOW correction.

## 3. Reachability analysis

The attacker must load a suitable BPF program that passes a packet pointer to a global subprogram, invokes a packet-mutating helper, and then accesses the preserved argument. Loading relevant networking BPF programs is privilege-gated in common configurations, but the supplied evidence does not resolve the exact program type, capability checks, attachment mechanism, or evaluated product configuration.

`HostAdminRequired=UNKNOWN` because the complete load, attach, and trigger sequence is not visible. Delegated `CAP_BPF` or networking capabilities could permit a below-host-admin actor, but theoretical delegation is insufficient to set it to `NO`.

`NamespaceScopedPrivilege=UNKNOWN` because namespace-local netdevice administration does not prove that BPF loading, attachment, and execution are all available through attacker-created namespaces. Root-controlled unprivileged-BPF policy may also be relevant. No special hardware or race timing is required.

## 4. Primitive and severity interpretation

The exact primitive is a verifier-approved stale packet-memory access. A `PTR_TO_PACKET` argument is represented inside the global subprogram as ordinary `PTR_TO_MEM`. A `pskb_*` operation may change or reallocate packet data, but the verifier fails to invalidate that argument. Subsequent BPF instructions can therefore read or write through a pointer into an invalidated region.

This is stale mutable packet storage rather than a stale structured kernel object. It is broader than a cleanup-only fault because attacker-authored instructions actively consume the pointer after invalidation. A UAF is directly implied for paths where the packet backing allocation is replaced and freed. Other mutations may instead produce stale bounds or an invalid in-buffer location.

The demonstrated primitive is Class B. A kernel crash is credible. Kernel disclosure, corruption of a reclaimed object, privilege escalation, and container escape remain unresolved consequences. Class A is not justified without controlled reclaim, a directed target, protected-data disclosure, or another concrete exploitation primitive.

`ImportantCandidate=YES` because a BPF verifier bypass permits programmable kernel-context access through potentially freed packet memory. `AutoDowngradeAllowed=NO` because reducing it to crash-only behavior would discard meaningful unresolved post-lifetime read/write leverage.

## 5. One-sentence report phrase

A BPF verifier type mismatch can preserve a packet pointer after a mutating subprogram invalidates its backing memory, permitting verifier-approved stale reads or writes with kernel crash and unresolved privilege-escalation potential.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

The patch establishes a programmable stale packet-memory access in kernel context, while reclaim control and the complete BPF privilege boundary require further analysis.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: bpf: Reject pkt arguments in mutating subprogs [ Upstream
Commit: 0b6b2bb9b90ad1e2d94d18f626258a1dbbdee0ea
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b6b2bb9b90ad1e2d94d18f626258a1dbbdee0ea

Changed files:
  kernel/bpf/verifier.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=0b6b2bb9b90ad1e2d94d18f626258a1dbbdee0ea

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

The original Linux kernel CVE announcement for CVE-2026-98589 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98589

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 5
  Paranoid ActionableScore: 6

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).