[CVE-2026-90347][MODERATE 7.0] arm64: ptrace: Keep 'orig_x0' in-sync with x0 on syscall entry [ Upstream

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

CVE: CVE-2026-90347
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: arm64: ptrace: Keep 'orig_x0' in-sync with x0 on syscall entry [ Upstream
Commit: f433869f23841a50455c4087d85540d5b4d37cde
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f433869f23841a50455c4087d85540d5b4d37cde
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90347
Analysis date: Fri, 18 Sep 2026 08:01:58 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90347 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90347

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.

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

CVE-2026-90347	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90347 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:H/I:H/A:H';CWE-693;CWE-863;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L';BEST CVSS score: '7.8';DESCR 'On arm64, a tracer can modify x0 during a seccomp ptrace stop while orig_x0 remains stale. Seccomp and audit may therefore validate the old first syscall argument while the kernel dispatches the syscall with the new value, allowing a traced process to bypass argument based seccomp restrictions. For the CVSS the PR:L value is used because exploitation requires local code execution and permission to trace the affected task, but it does not require full administrative privileges. The issue is not network reachable and does not directly provide kernel memory corruption or elevated Unix credentials. Impact depends on the sandbox policy and may range from limited policy bypass to substantial confidentiality, integrity, and availability impact when seccomp is the primary isolation boundary.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)  SKIP CVE-2026-90347 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	INIT TRACE HARDWARE  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap changed the score.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 Concrete authorization decision bypass. Seccomp can validate the stale `orig_x0`, while syscall dispatch uses the tracer-modified `x0`, allowing an unchecked first syscall argument.
* +1 Local unprivileged trigger. A same-UID tracer with an allowed ptrace relationship can exercise the path without host-administrator privileges.
* +1 Practical exploit chain. The complete sequence is established: ptrace modifies `x0`, seccomp re-evaluates the stale value, and the syscall executes with the modified value.
* +1 Integrity impact. Audit can observe the stale argument rather than the argument actually dispatched, creating a concrete security-record inconsistency in addition to the seccomp bypass.
* No memory-corruption, UAF, OOB access, arbitrary-write, or controlled-reclaim points were awarded.
* No confidentiality point was awarded because no protected data or sensitive resource access is demonstrated.
* No privileged FD theft, credential access, root acquisition, or arbitrary privileged execution is established.
* No remote-reachability point was awarded.
* No additional semantic-reinterpretation points were stacked because the argument mismatch is already represented by the authorization-bypass and practical-chain signals.
* The paranoid score was not increased from speculative sandbox escape or LPE consequences.

3. Reachability analysis

The trigger requires an arm64 task stopped on syscall entry through ptrace, with seccomp using `SECCOMP_RET_TRACE`. The tracer must be permitted to modify the target registers, but this can be done below host-admin privilege through an ordinary same-UID parent-child tracing relationship.

No namespace capability is required, and user or network namespaces do not establish or materially change the complete trigger. No separate host-privileged setup, special hardware, boot option, or timing race is indicated. A seccomp tracing configuration is required, but it is part of the vulnerable mechanism rather than proof of host-admin dependence.

The demonstrated attacker controls the tracer and traced task relationship. No supplied evidence establishes exploitation against an unrelated privileged process or a path from this bypass to root privileges.

4. Primitive and severity interpretation

The exact primitive is a security-policy time-of-check versus use mismatch between `orig_x0` and `x0`. Seccomp and audit inspect one first-argument value, while syscall dispatch can consume another value selected by the tracer.

This is not a lifetime violation and does not involve stale storage after object destruction. There is no repeated release or refcount mutation. The classification is CLASS_A because a mandatory seccomp authorization check is concretely bypassed and the unchecked argument is used by an externally meaningful kernel operation.

The demonstrated consequences are argument-based seccomp policy bypass and inaccurate audit interpretation. Broader confidentiality compromise, privilege escalation, and sandbox escape depend on the process credentials, available syscalls, and surrounding sandbox policy and are not established by this patch alone.

ImportantCandidate is YES because this is a direct security-boundary bypass rather than ordinary invalid-state behavior. AutoDowngradeAllowed is NO because automatically treating it as an ordinary Moderate issue could discard a meaningful seccomp enforcement failure. Operational severity is Actionable Moderate at minimum, with Important classification dependent on downstream sandbox consequences.

5. One-sentence report phrase

On arm64, a ptrace tracer can change the first syscall argument after seccomp inspection while leaving orig_x0 stale, allowing syscall dispatch with an argument that was not subjected to the intended seccomp and audit checks.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The direct seccomp boundary bypass is established, but product-specific review is required to determine which forbidden operations and protected resources become reachable in affected sandbox configurations.

7. Call-site confidence

Call-site confidence: high

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

Patch: arm64: ptrace: Keep 'orig_x0' in-sync with x0 on syscall entry [ Upstream
Commit: f433869f23841a50455c4087d85540d5b4d37cde
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f433869f23841a50455c4087d85540d5b4d37cde

Changed files:
  arch/arm64/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=f433869f23841a50455c4087d85540d5b4d37cde

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

The original Linux kernel CVE announcement for CVE-2026-90347 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90347

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:L/A:L
  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: unknown
  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).