[CVE-2026-93222][LOW] signal: avoid shared siginfo namespace rewrites

[CVE-2026-93222][LOW] signal: avoid shared siginfo namespace rewrites

[AL-KERNEL]

CVE: CVE-2026-93222
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: signal: avoid shared siginfo namespace rewrites
Commit: e015d1ac6b43a23c52c5163299414ae77d7d4ae0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e015d1ac6b43a23c52c5163299414ae77d7d4ae0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93222
Analysis date: Thu, 24 Sep 2026 12:19:06 -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-2026-93222 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93222

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: LOW
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-2026-93222	LOW	https://www.kernelcve.org/list/?q=CVE-2026-93222 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:L/A:N';CWE-345;CWE-668;CWE-682;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '3.3';DESCR 'A shared siginfo object can be rewritten for the user namespace of one signal recipient and then reused for another recipient during group signal delivery. This can cause a later recipient to observe incorrect si_pid or si_uid sender metadata translated for a different namespace. For the CVSS the PR:L applies because an attacker needs local process execution and permission to send a signal to the affected process group. The issue is not network reachable. The demonstrated impact is limited integrity impact from incorrect signal sender attribution. The patch context does not show a memory corruption primitive, kernel permission bypass, privilege escalation, information disclosure, or denial of service. The base score uses AC:H because the trigger requires a suitable multi namespace group signal configuration. The paranoid score uses AC:L because no timing race is required once such a configuration exists.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	SIMPLEFIX LINUS 	YES	NO	checked

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

ActionableScore=1
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Local unprivileged trigger. An ordinary local user can create and signal processes under the same signal-permission domain. A suitable process group and different user namespace contexts are required, but no host-admin-equivalent capability is inherently required by the demonstrated path.
* No memory-corruption points. The patch copies a stack-local `kernel_siginfo`; it does not fix a UAF, OOB access, refcount error, stale pointer, or write primitive.
* No authorization-bypass points. Sender credentials are checked before signal delivery. The incorrect `si_pid` or `si_uid` representation affects delivered metadata, not the kernel decision allowing the signal.
* No confidentiality points. No protected data disclosure path is established.
* No integrity bonus beyond the local-trigger signal. Incorrect sender identity metadata is demonstrated, but no security-sensitive kernel or userspace decision consuming that metadata is supplied.
* No availability points. No crash, hang, resource exhaustion, or fatal signal-processing effect is established.
* No remote-reachability points. The path is invoked by local signal delivery.
* No negative privilege penalty. Host-admin-equivalent privilege is not established as a prerequisite.
* No hard-race penalty. This is deterministic shared-input mutation during sequential group delivery, not a timing-dependent race.

3. Reachability analysis

The evaluated attacker is a local process. The attacker needs permission to signal the target process group, normally satisfied for processes owned by the same user. The triggering configuration requires group signal delivery where recipients have different relevant user-namespace contexts, causing the first recipient-specific sender-ID translation to be reused for a later recipient.

No host root, `CAP_SYS_ADMIN`, or host `CAP_KILL` requirement is established by the patch. However, complete real-world reachability can depend on whether unprivileged user namespaces are enabled and on the process-group topology. The patch does not establish that a namespace-scoped capability is required or that every necessary setup stage is namespace-delegable, so `NamespaceScopedPrivilege=UNKNOWN`.

There is no network input, device requirement, special hardware requirement, boot parameter, or privileged prior host configuration identified in the supplied evidence.

4. Primitive and severity interpretation

The exact defect is a shared mutable `kernel_siginfo` object. `send_signal_locked()` rewrites `si_pid` and `si_uid` to represent the sender in the target task user namespace. For a group signal, a subsequent target can observe values rewritten for a previous target rather than values translated for its own namespace.

This is a metadata-consistency and identity-attribution logic flaw. It is neither active structured-object lifetime corruption nor fixed stale storage. There is no first lifetime operation, no dangling reference, no second refcount mutation, and no UAF.

The demonstrated consequence is incorrect sender metadata delivered to a signal recipient. A stronger consequence would require separate evidence that a security-sensitive recipient trusts the incorrect `siginfo` values to authorize an operation or disclose protected data. Such a downstream security decision is not shown. Therefore the issue is `PrimitiveClass=NONE`, is not an Important candidate, and may be automatically downgraded or closed after normal tracking.

5. One-sentence report phrase

A shared siginfo object can be rewritten for one recipient user namespace and reused for another recipient during group signal delivery, causing incorrect si_pid or si_uid sender metadata without a demonstrated memory corruption, authorization bypass, or denial of service consequence.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes only incorrect namespace-translated signal metadata, with no demonstrated kernel corruption, protected-resource access, privilege escalation, network exposure, or availability impact.

7. Call-site confidence

Call-site confidence: medium

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

Patch: signal: avoid shared siginfo namespace rewrites
Commit: e015d1ac6b43a23c52c5163299414ae77d7d4ae0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e015d1ac6b43a23c52c5163299414ae77d7d4ae0

Commit description:

send_signal_locked() rewrites sender ids for the target namespace.  Group
sends reuse the same siginfo, so one recipient can affect the next.

Copy the siginfo before changing it.

Link: https://lore.kernel.org/86a8857d58d43ee26a8b365b837fd24830343494.1782159692.git.include@grrlz.net
Fixes: 7a0cf09 ("signal: Correct namespace fixups of si_pid and si_uid")
Signed-off-by: Bradley Morgan <include@grrlz.net>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Adrian Huang <adrianhuang0701@gmail.com>
Cc: Aleksandr Nogikh <nogikh@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Marco Elver <elver@google.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/signal.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=e015d1ac6b43a23c52c5163299414ae77d7d4ae0

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

The original Linux kernel CVE announcement for CVE-2026-93222 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93222

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:H/PR:L/UI:N/S:U/C:N/I:L/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
  The Best / paranoid CVSS score: 3.3

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).