[CVE-2026-98627][IMPORTANT] bpf: Preserve packet pointer class displacement in regsafe() [ Upstream

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

CVE: CVE-2026-98627
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: bpf: Preserve packet pointer class displacement in regsafe() [ Upstream
Commit: 091b40845bd3cf96791171ca95113e9184ccb596
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=091b40845bd3cf96791171ca95113e9184ccb596
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98627
Analysis date: Sat, 24 Oct 2026 02:57:17 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
BPF verifier pruning can lose the displacement relationship among shared-ID packet pointers and admit a crafted out-of-bounds packet access with unresolved write and privilege-escalation leverage.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98627 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98627

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-98627	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-98627 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT IMPORTANT AEGIS_AS=2 LEGACY=IMPORTANT RESULT=SAME (final reconciliation agrees; DECISION: both IMPORTANT)	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-125;*CWE-787;CWE-682;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 'An unsound state pruning decision in BPF regsafe can lose the displacement between packet pointers that share an ID. A bounds check on one pointer updates the shared packet range, so pruning a state after the relative displacement changed can allow another pointer to perform an out of bounds packet access. This is a verifier protection failure with a concrete potential OOB read or OOB write primitive, although the available offset range and reliability of reaching adjacent kernel objects require exploit validation. For the CVSS the PR:L value reflects that an attacker must execute locally and load a crafted packet processing BPF program, while required capabilities depend on whether unprivileged BPF is enabled or BPF access is delegated. The issue is not directly network reachable. Impact is at least kernel denial of service and may include kernel memory disclosure, corruption, or local privilege escalation. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 7.8 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. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was IMPORTANT. The shadow agreed with the final production impact and aggregation did not change that impact. 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	WRITE OOB BPF SIMPLEFIX IMPROVEONLY LINUS PACKET 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 4.
* Conservative score: 4; no floor or cap applied.
* Raw paranoid score: 5.
* Paranoid score: 5; the stronger reading treats the attacker-selected BPF access as potentially write-capable, as stated in the supplied triage evidence.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +1 weak/indirect corruption: verifier state pruning loses displacement between packet pointers sharing an ID, licensing a concrete out-of-bounds packet access.
* +1 practical primitive chain: crafted pointer displacement, shared-ID bounds propagation, unsound pruning, then later access through another class member.
* +1 reliable-crash concern: an accepted out-of-bounds packet access can plausibly fault or corrupt packet-adjacent storage; a guaranteed panic is not shown.
* +1 broad BPF verifier exposure: packet-processing BPF and verifier state pruning are deployed kernel functionality, although program-loading privilege varies.
* Paranoid replacement: +2 strong corruption instead of the base +1 weak-corruption signal, because supplied evidence supports a write-capable OOB access interpretation. This adds one net point.
* No privilege penalty: host-admin-equivalent privilege is not positively shown.
* No confidentiality, protected-state integrity, arbitrary write, adjacent victim, controlled target, disclosure, or LPE bonus is awarded.
* NEW52/B5-R does not apply: no retry-accumulated index or retry sequence exists.
* B4 does not apply: this is verifier memory-safety enforcement, not an authorization DENY-to-ALLOW decision.

3. Reachability analysis

A local actor must load and execute a crafted packet-processing BPF program. The evidence does not establish whether the complete load/attach/trigger sequence is available to an ordinary user, delegated capability holder, namespace-scoped administrator, or only host administration. Unprivileged BPF configuration, CAP_BPF/CAP_SYS_ADMIN requirements, attachment privilege, and netdevice control are unresolved. Remote packet reachability alone is insufficient because the crafted program must first be installed. No special hardware or timing race is required.

4. Primitive and severity reading

The primitive is an unsound verifier equivalence decision: registers with the same packet-pointer ID but changed relative displacement can be treated as safely covered by an explored state. Shared range propagation then authorizes an access outside the packet’s validated bounds.

This is not a UAF and not NEW52 retry accumulation. The patch establishes an OOB packet access, but does not identify its exact width, destination, adjacent object, or a completed kernel-memory write exploit. Therefore CLASS_B is more supportable than CLASS_A. The write-capable interpretation is technically credible but requires call-path and generated-instruction validation.

ImportantCandidate is YES because a crafted verifier state can escape memory-safety validation and reach a later access; exploit leverage beyond crash remains materially unresolved. Auto-downgrade is unsafe despite the absence of a demonstrated LPE.

5. One-sentence report phrase

BPF verifier pruning can lose the displacement relationship among shared-ID packet pointers and admit a crafted out-of-bounds packet access with unresolved write and privilege-escalation leverage.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm a write-form reproducer, access width and backing layout, plus the exact BPF load/attach privilege boundary.

7. Call-site confidence

Call-site confidence: medium

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

Patch: bpf: Preserve packet pointer class displacement in regsafe() [ Upstream
Commit: 091b40845bd3cf96791171ca95113e9184ccb596
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=091b40845bd3cf96791171ca95113e9184ccb596

Changed files:
  kernel/bpf/states.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=091b40845bd3cf96791171ca95113e9184ccb596

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

The original Linux kernel CVE announcement for CVE-2026-98627 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98627

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: 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: 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).