[CVE-2026-98590][MODERATE 7.0] bpf: Fix bpf_sock context code generation [ Upstream

[CVE-2026-98590][MODERATE 7.0] bpf: Fix bpf_sock context code generation [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98590
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Fix bpf_sock context code generation [ Upstream
Commit: e3ddcf4aeb342d4de2e5761c7042270d454752de
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3ddcf4aeb342d4de2e5761c7042270d454752de
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98590
Analysis date: Sun, 18 Oct 2026 23:55:46 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A width mismatch in bpf_sock context code generation allows a crafted BPF program to produce a runtime value outside the verifier approved range, creating an unresolved verifier bypass that requires manual review for possible kernel memory safety impact.

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

The original Linux kernel CVE announcement for CVE-2026-98590 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98590

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-2026-98590	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98590 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 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-681;CWE-682;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'The bpf_sock context access generator can place the special rx_queue_mapping value into a 64 bit register while the verifier assumes that the upper 32 bits are zero. A crafted BPF program can shift or otherwise transform this value and obtain a runtime result outside the range accepted by the verifier. This creates a verifier and runtime mismatch that may permit bounds reasoning to be bypassed and can potentially lead to kernel memory access, a kernel crash, or local privilege escalation. For the CVSS the PR:L value is used for the paranoid score because the issue may be reachable by an unprivileged BPF user on systems that enable such loading, or by a restricted container or service account with delegated BPF capabilities. The issue is not directly network reachable and requires local execution of a suitable BPF program. Impact is at least a local security boundary violation and denial of service, with possible high confidentiality and integrity impact if the verifier mismatch can be converted into controlled kernel memory access. Automated impact decision path. The original SimpleNet classifier selected LOW. 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. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the manual review requirement was applied. 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. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 1 with primitive class CLASS_C and manual review RECOMMENDED. 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 5)	MAYBE	REMOTE BPF SIMPLEFIX LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4
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 conservative score: 4
* Conservative score: 4. No floor or cap changed the result.
* Raw paranoid score: 5
* Paranoid score: 5. The host-privileged BPF cap does not change it.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 Strong attacker-influenced semantic reinterpretation. The verifier models the value as zero-extended and width-limited, while generated code can produce the 64-bit value `0xffffffffffffffff`. Attacker-selected BPF operations can consume a value outside the verified range.
* +1 Memory-layout and width invariant restoration. The patch corrects both the emitted MOV width and the reported destination-field size. This scores the explicit verifier/code-generation width contract, not another corruption consequence.
* +1 Weak exploitation concern. The mismatch is security-relevant because a crafted program can shift the value and invalidate verifier range assumptions. This is stronger than an ordinary wrong scalar value but does not establish arbitrary access.
* Paranoid +1 Downstream memory-access concern. BPF verifier range information can govern later bounds or pointer reasoning, so conversion into an invalid kernel memory operation is technically credible but not demonstrated by the supplied code.

Not awarded:

* No UAF, OOB write, controlled reclaim, arbitrary read/write, disclosure, kernel crash, or LPE is demonstrated.
* No local-unprivileged bonus because the complete BPF load and attach path is unresolved.
* No remote-reachability or namespace-reachability bonus.
* No C/I consequence points based only on the theoretical ability to convert verifier unsoundness into memory access.
* B5-R does not apply because no retry-accumulated heap OOB write exists.
* B3-PENDING, V32, V33, and V34 do not apply.
* B4-PENDING does not apply because this is a verifier safety-model mismatch, not an authorization guard changing DENY to ALLOW.

3. Reachability analysis

A crafted BPF program must read `bpf_sock.rx_queue_mapping`, reach the special `NO_QUEUE_MAPPING` case, and transform the result so that the runtime value exceeds the verifier model.

The exact program type, load privilege, attachment privilege, governing capability namespace, and relevant `kernel.unprivileged_bpf_disabled` state are not supplied. Modern deployments commonly restrict BPF loading, but that does not prove host-admin-equivalent privilege for this complete path. Therefore both host-admin and namespace-scoped reachability remain UNKNOWN.

There is no direct network trigger. Network activity may influence socket state after a program is installed, but installation and execution of the crafted BPF program remain prerequisites. No race, retry sequence, unusual hardware, or timing window is required by the demonstrated mismatch.

4. Primitive and severity interpretation

The exact primitive is a verifier/runtime inconsistency in active BPF register state. The verifier assumes a 32-bit zero-extended result, but generated instructions can create a sign-extended 64-bit value. The attacker-controlled BPF program can then consume a value that the verifier considered impossible.

This is not a UAF, fixed stale-storage issue, cleanup defect, authorization bypass, or demonstrated kernel-memory overwrite. It is classified as CLASS_A because the patch directly establishes a strong active semantic reinterpretation across the BPF verifier security boundary.

The demonstrated consequence is violation of verifier range assumptions. Potential kernel memory access, crash, or privilege escalation remains unresolved rather than proven. ImportantCandidate is YES because verifier unsoundness can invalidate the primary BPF memory-safety boundary and warrants Important-versus-Moderate review. AutoDowngradeAllowed is NO because automatically treating the defect as an ordinary wrong-value bug would discard this concrete security-boundary primitive.

5. One-sentence report phrase

A width mismatch in bpf_sock context code generation allows a crafted BPF program to produce a runtime value outside the verifier approved range, creating an unresolved verifier bypass that requires manual review for possible kernel memory safety impact.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Review the affected BPF program types, load and attach permissions, unprivileged BPF configurations, and whether the impossible scalar range can feed pointer arithmetic or bounds-checked kernel memory operations.

7. Call-site confidence

Call-site confidence: medium

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

Patch: bpf: Fix bpf_sock context code generation [ Upstream
Commit: e3ddcf4aeb342d4de2e5761c7042270d454752de
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3ddcf4aeb342d4de2e5761c7042270d454752de

Changed files:
  net/core/filter.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=e3ddcf4aeb342d4de2e5761c7042270d454752de

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

The original Linux kernel CVE announcement for CVE-2026-98590 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98590

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: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: 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).