[CVE-2026-98572][MODERATE 7.0] bpf: Fix immediate JMP JEQ/JNE on MIPS32 [ Upstream

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

CVE: CVE-2026-98572
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Fix immediate JMP JEQ/JNE on MIPS32 [ Upstream
Commit: 1547e9f3a7d71971216e6dba30270cae13fe4e02
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1547e9f3a7d71971216e6dba30270cae13fe4e02
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98572
Analysis date: Sat, 24 Oct 2026 10:56:27 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
The MIPS32 eBPF JIT miscompiles negative-immediate JEQ/JNE operations, creating a concrete verifier-to-native control-flow semantic mismatch without a demonstrated memory-safety exploit.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98572 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98572

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
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CVE-2026-98572	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98572 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both 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-682;CWE-697;CWE-670;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '7';DESCR 'The MIPS32 eBPF JIT emitted addu instead of addiu while implementing negative immediate JEQ and JNE comparisons. The value 1 was consequently interpreted as register at which is mapped to BPF_REG_AX and is also used by constant blinding, producing an incorrect branch result. For the CVSS the PR:H base value reflects that loading attacker selected eBPF programs normally requires BPF related capabilities. For the CVSS the PR:L paranoid value covers systems with unprivileged BPF enabled or delegated BPF access. The confirmed impact is incorrect BPF program behavior, but the JIT and verifier semantic mismatch may invalidate branch specific verifier assumptions and could plausibly permit memory safety violations. No OOB access, arbitrary write, or privilege escalation primitive is directly demonstrated by the patch. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 3 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage MODERATE to MODERATE_KPANIC because 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 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_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. 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 3)	MAYBE	BPF SIMPLEFIX HARDWARE LINUS TEST  KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_A
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: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; no floor or cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* **+2 — Strong attacker-influenced semantic reinterpret:** the verifier/JIT input specifies an immediate comparison, but `addu` interprets operand `1` as register `$at`. The generated native branch therefore has materially different control-flow semantics from the verified BPF instruction.
* **Paranoid +1 — Weak exploitation concern:** a concrete verifier/JIT control-flow mismatch can invalidate branch-specific verifier assumptions. This is technically plausible here, but no program demonstrating unsafe memory access is supplied.
* No OOB access, arbitrary write, controlled reclaim, callback control, disclosure, crash, or privilege escalation is shown.
* No confidentiality or protected-state integrity point is awarded for incorrect program behavior alone.
* No privilege, rarity, or race penalty is applied: exact loading privileges and deployment exposure are unresolved, while no race exists.

3. Reachability analysis

An attacker must load attacker-selected eBPF and obtain execution through the MIPS32 JIT. The evidence does not establish whether the complete load/JIT/trigger sequence is available to an unprivileged user, a delegated `CAP_BPF` user, namespace capabilities, or only a host administrator. MIPS32 and JIT enablement narrow exposure, but are not sufficient proof of a rare-and-difficult configuration penalty.

4. Primitive and severity reading

The primitive is a verified-bytecode/native-code semantic mismatch affecting active branch execution, not a UAF or demonstrated memory corruption. It is CLASS_A under semantic reinterpretation, but the proven effect is limited to an incorrect comparison result. Memory-safety violation or LPE remains speculative. Important review is retained because verifier/JIT semantic equivalence is a security invariant; automatic downgrade could discard a real control-flow primitive.

5. One-sentence report phrase

The MIPS32 eBPF JIT miscompiles negative-immediate JEQ/JNE operations, creating a concrete verifier-to-native control-flow semantic mismatch without a demonstrated memory-safety exploit.

6. Manual review advice

MANUAL CHECK REQUIRED

Review whether a verifier-accepted program can use the incorrect branch to reach operations that are unsafe under the generated control flow.

7. Call-site confidence

Call-site confidence: medium

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

Patch: bpf: Fix immediate JMP JEQ/JNE on MIPS32 [ Upstream
Commit: 1547e9f3a7d71971216e6dba30270cae13fe4e02
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1547e9f3a7d71971216e6dba30270cae13fe4e02

Changed files:
  arch/mips/net/bpf_jit_comp32.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=1547e9f3a7d71971216e6dba30270cae13fe4e02

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

The original Linux kernel CVE announcement for CVE-2026-98572 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98572

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:H/UI:N/S:U/C:N/I:L/A:L
  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: 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: 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).