[CVE-2026-98611][MODERATE REGULAR] bpf: Check params size before reading reserved fields [ Upstream

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

CVE: CVE-2026-98611
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: Check params size before reading reserved fields [ Upstream
Commit: e03253f5d65ebcd2a6d479f140c3bd9c7e4fb84a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e03253f5d65ebcd2a6d479f140c3bd9c7e4fb84a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98611
Analysis date: Mon, 19 Oct 2026 02:52:24 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A BPF program can make `bpf_crypto_ctx_create()` read two bytes beyond its verifier-validated parameter region, with no demonstrated disclosure or write primitive but with a possible local kernel fault if the buffer crosses an inaccessible boundary.

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

The original Linux kernel CVE announcement for CVE-2026-98611 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98611

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-2026-98611	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98611 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF V39_AEGIS_ONE_STEP_UP=LOW->MODERATE TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: 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:N/I:N/A:H';CWE-125;*CWE-20;CWE-1284;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'bpf_crypto_ctx_create reads params reserved bytes before verifying that params size covers the complete bpf_crypto_params structure. A local BPF program can therefore provide a shorter verifier validated region and cause the kernel to read two bytes beyond that region. The demonstrated primitive is an out of bounds read with no supported write primitive and no direct disclosure channel because an invalid size results in EINVAL regardless of the reserved byte values. A carefully placed buffer could potentially make the invalid read cross an inaccessible boundary and cause a kernel fault or denial of service. For the CVSS the PR:L value is used for the paranoid score because a capability scoped service account, container root, or delegated BPF operator may be able to load or attach the relevant TC or XDP program without having unrestricted host administration. The issue is not directly network reachable because attacker controlled packets alone do not invoke the invalid call without an attacker controlled BPF program. Impact is most plausibly local denial of service and the source does not support privilege escalation or integrity modification. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 2 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 1 with primitive class CLASS_C and manual review RECOMMENDED. 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.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	BPF SIMPLEFIX IMPROVEONLY LINUS KPANIC_UNSUPPORTED_REMOVED V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=2
ActionableScoreLower=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 conservative score: 1
* Conservative score: 1
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap changed either score.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Conservative signals:

* +1 confirmed bounded kernel out-of-bounds read. `bpf_crypto_ctx_create()` reads `reserved[0]` and `reserved[1]` beyond the verifier-validated `params__sz` region.
* No privilege penalty. The complete BPF load, kfunc invocation, TC or XDP attachment, and namespace privilege chain is unresolved, so host-admin privilege is not assumed.

Additional paranoid signal:

* +1 plausible kernel fault. A deliberately positioned short buffer could make one of the two invalid reads cross an inaccessible boundary, although the patch provides no demonstrated crash.

Important non-awarded signals:

* No confidentiality point. An invalid size ultimately returns `EINVAL` regardless of the out-of-bounds byte values, and no byte-copy or disclosure path is shown.
* No integrity point. There is no write, UAF, type confusion, refcount mutation, or active-state corruption.
* No remote-reachability point. Network packets alone do not invoke the kfunc without an attacker-controlled BPF program.
* No B5-R signal. There is no heap OOB write, retry-accumulated offset, or subsequent consumption of corrupted state.
* No B3-PENDING signal. No shared-backing write occurs.
* No V33 or V34 signal. No attacker-influenced active structured state is modified.
* No authorization signal. The reordered condition is a memory-size validation fix, not a DENY-to-ALLOW authorization correction.
* No additional availability point. A crash is only a paranoid possibility and no distinct persistent effect is established.

3. Reachability analysis

A BPF program able to call `bpf_crypto_ctx_create()` can supply a pointer with a deliberately short `params__sz`. The affected API was introduced for TC and XDP programs.

The supplied context does not establish the complete privilege boundary. BPF program loading may require `CAP_BPF`, `CAP_SYS_ADMIN`, or another privileged configuration. TC or XDP attachment may independently require `CAP_NET_ADMIN` over the relevant device. It is not established that all stages work with capabilities obtained in an attacker-created namespace.

Accordingly, `HostAdminRequired` and `NamespaceScopedPrivilege` remain `UNKNOWN`. No ordinary unprivileged trigger bonus or host-admin penalty is applied. This is not directly network-triggerable, requires no race, and has no special hardware prerequisite.

4. Primitive and severity interpretation

The exact primitive is a two-byte read beyond the memory region validated by the BPF verifier. It is not a read beyond `struct bpf_crypto_params` after successful size validation. It occurs specifically because the reserved fields are evaluated before the structure-size comparison.

The out-of-bounds values affect short-circuit evaluation, but all short-buffer cases return `EINVAL`. Therefore, the supplied code does not establish a usable disclosure oracle, control-flow primitive, subsequent write, or protected-resource access.

This is `CLASS_C`: a concrete invalid read with possible crash impact but no independently useful corruption primitive. It is not a UAF and does not involve active structured-state corruption. `ImportantCandidate=NO` because no write, disclosure, authorization bypass, or privilege-escalation mechanism is supported. `AutoDowngradeAllowed=YES` because the remaining uncertainty concerns crashability and privilege scope rather than an unresolved Important-grade primitive.

Likely operational severity is Low to ordinary Moderate, depending on whether an eligible BPF program can place the short region at a faulting boundary.

5. One-sentence report phrase

A BPF program can make `bpf_crypto_ctx_create()` read two bytes beyond its verifier-validated parameter region, with no demonstrated disclosure or write primitive but with a possible local kernel fault if the buffer crosses an inaccessible boundary.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm the eligible BPF program types, kfunc registration constraints, required load and attach capabilities, permitted pointer classes, and whether a verifier-valid short region can be positioned at a reliably faulting boundary.

7. Call-site confidence

Call-site confidence: medium

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

Patch: bpf: Check params size before reading reserved fields [ Upstream
Commit: e03253f5d65ebcd2a6d479f140c3bd9c7e4fb84a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e03253f5d65ebcd2a6d479f140c3bd9c7e4fb84a

Changed files:
  kernel/bpf/crypto.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=e03253f5d65ebcd2a6d479f140c3bd9c7e4fb84a

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

The original Linux kernel CVE announcement for CVE-2026-98611 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98611

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: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: 1
  Paranoid ActionableScore: 2

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).