* [CVE-2026-98043][MODERATE REGULAR] bpf: Don't infer non-NULL from a pointer with an unbounded offset [ Upstream
@ 2026-09-28 23:00 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-28 23:00 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98043
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: Don't infer non-NULL from a pointer with an unbounded offset [ Upstream
Commit: cb6642048739bf4ee5aa09fe465511f1e87caa63
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cb6642048739bf4ee5aa09fe465511f1e87caa63
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98043
Analysis date: Mon, 28 Sep 2026 19:00:03 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98043 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98043
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98043 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98043 CHECK WITH IMPACT FROM ORIG NN LOW 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:H';**CWE-476;*CWE-20;CWE-682;BEST CVSS score: '5.5';DESCR 'The BPF verifier can incorrectly infer that a nullable pointer is non-NULL when another pointer with an unbounded arithmetic offset wraps to zero at runtime. A crafted BPF program can use this incorrect branch refinement to pass verifier checks and then dereference a NULL map value pointer in kernel context, resulting in an Oops or kernel panic. For the CVSS the PR:L value is selected because an attacker must be able to load and execute a BPF program through a local process, either through delegated BPF capabilities or through unprivileged BPF when it is enabled. The issue is not network reachable. The demonstrated primitive is a NULL pointer dereference rather than a UAF, OOB access, or arbitrary write, so the supported impact is local denial of service without a proven confidentiality or integrity impact.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE NULLPTR BPF LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap changed either score.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Reliable kernel crash or strong DoS. The supplied BPF program demonstrates verifier acceptance followed by a kernel-context NULL-pointer dereference, which can cause an Oops or panic.
* +0 Weak corruption concern. The established primitive is an invalid NULL dereference with no useful target, reclaim, disclosure, or post-lifetime operation.
* No local-unprivileged bonus. The complete BPF load and execution path is not established as available to an ordinary user.
* No privilege penalty. Host-admin-equivalent privilege is not established, while reduced or namespace-scoped privilege for the complete trigger is also unresolved.
* No remote-reachability bonus. A local BPF program must be loaded and executed.
* No UAF or lifetime bonus. No object is freed and subsequently reused.
* No controlled reclaim, OOB access, arbitrary write, callback influence, information disclosure, or authorization bypass is demonstrated.
* No extra Availability point. It would double-count the same NULL-dereference crash.
* No paranoid escalation. A broader verifier exploit would require an additional primitive not established by this patch.
3. Reachability analysis
The attacker must load and execute a crafted BPF program. Depending on the evaluated system and program type, this may require CAP_BPF, related capabilities, or host-controlled permission to use BPF. Ordinary-user reachability is possible only where the relevant unprivileged BPF path is enabled and supports the complete load and execution sequence, which is not established here.
The patch does not identify an attach requirement, netdevice operation, capability namespace, or attacker-reachable namespace sequence. Therefore, neither below-host-admin reachability nor complete namespace-scoped reachability is proven. A root-controlled unprivileged-BPF policy may be a prerequisite in some deployments. No network trigger, race, special hardware, or timing dependency exists.
4. Primitive and severity interpretation
The exact primitive is a verifier soundness error in non-NULL inference. An unbounded pointer offset can make a verifier-tracked non-NULL pointer evaluate to zero at runtime. Equality-based branch refinement then incorrectly marks another nullable pointer as non-NULL, allowing a load through address zero.
This is neither active structured stale storage nor fixed stale storage because no lifetime violation exists. There is no first release, dangling reference, second refcount mutation, or repeated-release condition.
The issue is CLASS_C because the demonstrated behavior is a NULL-pointer dereference and crash. The patch supports local denial of service but does not establish UAF, useful memory corruption, disclosure, integrity modification, or privilege escalation. Broader exploitation through another program construction remains speculative and is not scored.
ImportantCandidate is NO because no Important-preserving primitive is established. AutoDowngradeAllowed is YES because the demonstrated behavior is constrained to invalid-state execution and crash, although verifier variants still merit review. Likely operational severity is Moderate.
5. One-sentence report phrase
A crafted local BPF program can exploit incorrect non-NULL pointer inference for an unbounded offset to trigger a kernel NULL-pointer dereference and denial of service, but no useful memory-corruption or privilege-escalation primitive is established.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Review related pointer-comparison and offset-refinement paths for variants, but the supplied case itself demonstrates only a NULL dereference and DoS.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: bpf: Don't infer non-NULL from a pointer with an unbounded offset [ Upstream
Commit: cb6642048739bf4ee5aa09fe465511f1e87caa63
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cb6642048739bf4ee5aa09fe465511f1e87caa63
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=cb6642048739bf4ee5aa09fe465511f1e87caa63
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98043 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98043
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: Not available
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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: unknown
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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