[CVE-2026-98626][MODERATE REGULAR] bpf: Restrict CO-RE poisoning to relocatable instructions [ Upstream

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

CVE: CVE-2026-98626
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: Restrict CO-RE poisoning to relocatable instructions [ Upstream
Commit: a8c47e62d9aea2d47a09e06c1682c59c21b92449
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a8c47e62d9aea2d47a09e06c1682c59c21b92449
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98626
Analysis date: Sat, 24 Oct 2026 05:10:53 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
Malformed CO-RE metadata could poison non-relocatable BPF instructions, but the supplied evidence shows verifier rejection or intentional dead-code poisoning rather than kernel compromise.

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

The original Linux kernel CVE announcement for CVE-2026-98626 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98626

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: NO

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-2026-98626	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98626 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE AEGIS_AS=0 LEGACY=MODERATE RESULT=SAME V39_AEGIS_ONE_STEP_UP=LOW->MODERATE (final reconciliation agrees; DECISION: both MODERATE)	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:L';*CWE-20;CWE-1287;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '3.3';DESCR 'Malformed CO-RE metadata can name any instruction offset. An unresolved relocation was poisoned before target validation, so metadata could replace jumps, calls, exits, register-source ALU operations, or unsupported loads with the invalid relocation marker instead of producing an immediate relocation error. The resulting reachable instruction should be rejected by the BPF verifier, while poisoning in dead code is intentional, so the patch does not establish verifier bypass, memory corruption, information disclosure, or a host kernel crash. For the CVSS the PR:L worst case represents a delegated BPF loader or service that accepts objects from a low privileged user. Direct BPF loading commonly requires CAP_BPF or CAP_SYS_ADMIN and is better represented by PR:H. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 3.3 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to MODERATE because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation 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 KPANIC_UNSUPPORTED_REMOVED and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 0 with primitive class NONE and manual review REQUIRED. Its independently reconciled impact was MODERATE. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	BPF IMPROVEONLY LINUS KPANIC_UNSUPPORTED_REMOVED V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=1
ActionableScoreLower=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 0.
* Conservative score: 0; no kernel-security consequence is established.
* Raw paranoid score: 1.
* Paranoid score: 1; malformed input can cause operation-level program rejection in a delegated-loader scenario.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* Base +0: poisoning can overwrite an unintended instruction in the userspace/in-kernel relocation buffer, but reachable poison is expected to be rejected by the BPF verifier and dead-code poisoning is intentional.
* Paranoid +1: a service accepting attacker-supplied BPF objects could experience failed loads or workload disruption. No host-wide or reliable kernel DoS is shown.
* No semantic-reinterpretation bonus: jumps, calls, exits, and unsupported forms can be replaced, but no altered instruction is shown to execute past verification.
* No OOB write, UAF, kernel-memory corruption, verifier bypass, disclosure, authorization bypass, protected-state change, or LPE is shown.
* B5-R and B3-PENDING do not apply: there is neither retry-accumulated heap corruption nor a shared-backing write.
* No privilege penalty: effective privilege for the complete affected path is unresolved rather than proven host-admin-only.

3. Reachability analysis

Malformed CO-RE metadata materially controls the relocation target. Direct BPF loading commonly requires CAP_BPF/CAP_SYS_ADMIN or equivalent policy, while the supplied hints identify a possible delegated loader accepting lower-privileged input. The complete loader, kernel BPF-load, and namespace-capability chain is not shown, so both host-admin and namespace-scoped reachability remain unknown. No race, special hardware, or retry sequence is involved.

4. Primitive and severity reading

The patch fixes validation ordering: unresolved relocations were poisoned before confirming that the target instruction had a relocatable class and operand form. This creates invalid program state, classified CLASS_C, not kernel corruption. The supported consequence is rejection of a reachable poison by the verifier; execution of attacker-selected replacement semantics is unproven. ImportantCandidate is therefore NO, and automatic downgrade is allowed.

5. One-sentence report phrase

Malformed CO-RE metadata could poison non-relocatable BPF instructions, but the supplied evidence shows verifier rejection or intentional dead-code poisoning rather than kernel compromise.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm in-kernel CO-RE callers and whether any path consumes poisoned instructions without normal verifier enforcement.

7. Call-site confidence

Call-site confidence: medium

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

Patch: bpf: Restrict CO-RE poisoning to relocatable instructions [ Upstream
Commit: a8c47e62d9aea2d47a09e06c1682c59c21b92449
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a8c47e62d9aea2d47a09e06c1682c59c21b92449

Changed files:
  tools/lib/bpf/relo_core.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=a8c47e62d9aea2d47a09e06c1682c59c21b92449

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

The original Linux kernel CVE announcement for CVE-2026-98626 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98626

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:H/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:L
  The Best / paranoid CVSS score: 3.3

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: 0
  Paranoid ActionableScore: 1

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).