[CVE-2026-98613][MODERATE REGULAR] bpf: Bound ownership depth through local kptrs and graph roots [ Upstream

[CVE-2026-98613][MODERATE REGULAR] bpf: Bound ownership depth through local kptrs and graph roots [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98613
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: Bound ownership depth through local kptrs and graph roots [ Upstream
Commit: 92aa0502c781d72bb9685245c3280efb3766a110
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=92aa0502c781d72bb9685245c3280efb3766a110
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98613
Analysis date: Sat, 24 Oct 2026 12:38:49 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
Crafted BPF local-object ownership chains can recursively exhaust the kernel stack when their head object is dropped, causing a host kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-98613 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98613

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-2026-98613	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98613 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=MODERATE RESULT=SAME (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:H';CWE-674;**CWE-400;CWE-770;BEST CVSS score: '5.5';DESCR 'Program allocated BPF objects can form cyclic or deeply nested ownership chains through local referenced kptrs and graph roots. Synchronous destruction follows each ownership edge through bpf_obj_free_fields() and __bpf_obj_drop_impl(), so dropping the head can exhaust the kernel stack and crash the host. For the CVSS the PR:L value reflects the need for a local user or process able to load BTF and BPF programs, allocate the affected objects, and trigger their destruction. The demonstrated primitive is uncontrolled recursion and kernel stack exhaustion rather than UAF, OOB access, or an arbitrary write, so the supported impact is availability loss without proven confidentiality or integrity impact. The issue is not directly network reachable. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. 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 has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 5.5 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	INIT BPF NOMEMCHK UAF HARDWARE LINUS TEST 	-	-	checked

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

ActionableScore=1
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: 1.
* Conservative score: 1; no floor or cap changed it.
* Raw paranoid score: 1.
* Paranoid score: 1; stronger impact would require unsupported memory-corruption or reachability assumptions.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Reliable kernel crash/strong DoS: attacker-defined local BTF ownership chains can make synchronous `bpf_obj_free_fields()` / `__bpf_obj_drop_impl()` recursion exhaust the kernel stack.
* +0 Additional availability: withheld because it would duplicate the same stack-exhaustion crash.
* No UAF, OOB read/write, arbitrary write, stale object, controlled reclaim, authorization bypass, confidentiality impact, or integrity impact is shown.
* No local-unprivileged bonus: the supplied evidence does not establish that the complete BTF load, BPF program load, object allocation, and destruction sequence works for a normal user.
* No privilege penalty: effective host-admin privilege is also not positively established.
* NEW52/B5-R does not apply: there is no retry-accumulated heap OOB write or later consumption of corrupted heap state.

3. Reachability analysis

A local process able to load the relevant BTF/BPF program can define recursive or excessively deep ownership through local referenced kptrs or graph roots, allocate those objects, and trigger destruction. Exact CAP_BPF/CAP_SYS_ADMIN policy and product settings are not supplied, so host-admin and namespace-scoped reachability remain unknown. No remote path, special hardware, prior device setup, or timing race is involved.

4. Primitive and severity reading

The primitive is attacker-shaped active ownership topology causing unbounded synchronous recursive destruction and kernel-stack exhaustion. It is neither fixed stale storage nor a lifetime violation: no object is shown used after free, and no repeated release through a dangling reference exists.

This is CLASS_C because the demonstrated consequence is host crash/availability loss without a separately useful corruption primitive. ImportantCandidate is NO and auto-downgrade is allowed because the fix adds a depth/cycle validation bound, while the evidence shows no memory corruption or security-boundary breach.

5. One-sentence report phrase

Crafted BPF local-object ownership chains can recursively exhaust the kernel stack when their head object is dropped, causing a host kernel crash.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm product-specific BPF loading privileges and whether delegated or namespace-scoped actors can complete the trigger.

7. Call-site confidence

Call-site confidence: high

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

Patch: bpf: Bound ownership depth through local kptrs and graph roots [ Upstream
Commit: 92aa0502c781d72bb9685245c3280efb3766a110
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=92aa0502c781d72bb9685245c3280efb3766a110

Changed files:
  kernel/bpf/btf.c
  tools/testing/selftests/bpf/prog_tests/linked_list.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=92aa0502c781d72bb9685245c3280efb3766a110

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

The original Linux kernel CVE announcement for CVE-2026-98613 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98613

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).