[CVE-2026-98951][MODERATE REGULAR] riscv: ptrace: Zero-initialize regset buffers before copyin [ Upstream

[CVE-2026-98951][MODERATE REGULAR] riscv: ptrace: Zero-initialize regset buffers before copyin [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98951
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: riscv: ptrace: Zero-initialize regset buffers before copyin [ Upstream
Commit: 89fc70d73f4ac8781f9e15edd1dbc6b6088453b3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=89fc70d73f4ac8781f9e15edd1dbc6b6088453b3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98951
Analysis date: Mon, 26 Oct 2026 16:01:35 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate
Manual review required: YES

Summary:
A short RISC-V `PTRACE_SETREGSET` can propagate uninitialized kernel-stack bytes into retrievable tracee vector state or an invalid shadow-stack pointer.

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

The original Linux kernel CVE announcement for CVE-2026-98951 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98951

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-98951	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98951 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE AEGIS_AS=2 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:H/I:N/A:L';*CWE-457;*CWE-200;CWE-665;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '6.1';DESCR 'A short PTRACE_SETREGSET request can leave part of a kernel stack regset buffer uninitialized because user_regset_copyin copies only the supplied count. In riscv_vr_set the residual bytes may be validated and stored in the target vector state, which creates a plausible kernel stack disclosure path if the state is later retrieved through PTRACE_GETREGSET. In riscv_cfi_set an uninitialized value may become the target shadow stack pointer and cause incorrect execution or a tracee crash. For the CVSS the PR:L value is selected because an attacker needs local execution and ptrace permission for the target process. The issue is not directly network reachable and there is no supported arbitrary kernel write or privilege escalation primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 6.1 and the production ActionableScore returned 4 with recommendation Actionable Moderate. 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. KP and FD specialist checks stage MODERATE_KPANIC to MODERATE because KP specialist did not establish a qualifying panic. 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 and DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP. The independent weaker Aegis shadow evaluated CVSS 4.4 and ActionableScore 2 with primitive class CLASS_B 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 Actionable Moderate (with actual score 4)	MAYBE	TRACE SIMPLEFIX SKIP HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3.
* Conservative score: 3; no floor or cap applied.
* Raw paranoid score: 4.
* Paranoid score: 4; no floor or cap applied.
* Final recommended bucket: **Actionable Moderate**::

2. Signal breakdown

* +1 Local unprivileged trigger: a same-credential process can ordinarily ptrace its own child and issue a short `PTRACE_SETREGSET`; host-administrator power is not inherently required.
* +1 Uninitialized kernel-stack data propagation: uncopied stack-buffer bytes are validated and stored in the tracee’s vector state or used as its shadow-stack pointer.
* +1 Confidentiality plausible: vector-state bytes stored in the tracee are plausibly retrievable through `PTRACE_GETREGSET`, potentially exposing residual stack contents.
* Paranoid +1 practical disclosure chain: short SETREGSET → residual stack bytes enter vstate → later GETREGSET. This is technically credible but not fully demonstrated by visible get-side source or an observed disclosure.
* No kernel OOB write, UAF, authorization bypass, arbitrary write, LPE, or kernel crash is shown. The CFI consequence is incorrect tracee state or tracee failure, not established host-wide DoS.
* No C:H award: leaked content, stability, and security sensitivity are not established.

3. Reachability analysis

The credible actor is a local, below-host-admin process with ptrace permission over a same-credential tracee, commonly its child. No host UID 0 or namespace capability is intrinsically needed. LSM/Yama policy may restrict particular deployments, but does not make host-admin privilege a demonstrated complete-trigger requirement. RISC-V vector or CFI regsets must be available; no race, unusual hardware, or prior privileged setup is shown.

4. Primitive and severity reading

The primitive is partial initialization of stack-backed regset structures followed by consumption of residual bytes as active tracee state. It is CLASS_B because it provides a plausible bounded kernel-stack disclosure path and can corrupt tracee execution state, but no strong memory-corruption or protected-state primitive is proven. ImportantCandidate is NO because sensitive leakage or a stronger exploit chain is unresolved. Auto-downgrade remains allowed, though manual verification is required to establish the GETREGSET read-back extent and leaked-byte quality.

5. One-sentence report phrase

A short RISC-V `PTRACE_SETREGSET` can propagate uninitialized kernel-stack bytes into retrievable tracee vector state or an invalid shadow-stack pointer.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm exact regset sizes, GETREGSET read-back, repeated leak stability, and whether exposed bytes contain security-relevant kernel data.

7. Call-site confidence

Call-site confidence: medium

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

Patch: riscv: ptrace: Zero-initialize regset buffers before copyin [ Upstream
Commit: 89fc70d73f4ac8781f9e15edd1dbc6b6088453b3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=89fc70d73f4ac8781f9e15edd1dbc6b6088453b3

Changed files:
  arch/riscv/kernel/ptrace.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=89fc70d73f4ac8781f9e15edd1dbc6b6088453b3

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

The original Linux kernel CVE announcement for CVE-2026-98951 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98951

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:L/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:L
  The Best / paranoid CVSS score: 6.1

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: 3
  Paranoid ActionableScore: 4

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).