[CVE-2026-99226][MODERATE 7.0] keys: Avoid the owner account dereference in named keyring lookup

[CVE-2026-99226][MODERATE 7.0] keys: Avoid the owner account dereference in named keyring lookup

[AL-KERNEL]

CVE: CVE-2026-99226
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: keys: Avoid the owner account dereference in named keyring lookup
Commit: 77249d4b1bb5ad43552b7023c4a0978937aa7a56
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=77249d4b1bb5ad43552b7023c4a0978937aa7a56
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99226
Analysis date: Mon, 02 Nov 2026 22:27:57 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A concurrent keyring ownership change can free `keyring->user` while named lookup reads its UID, causing a confirmed four-byte slab UAF read and possible kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-99226 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99226

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-2026-99226	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99226 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A race in find_keyring_by_name can dereference a freed key_user when a named session keyring join overlaps KEYCTL_CHOWN. keyring_name_lock keeps the keyring alive but does not protect keyring user, so an ownership replacement can drop the final reference and cause a 4 byte use after free read of the old owner UID. For the CVSS the PR:L value in the paranoid score reflects delegated namespace administration or another limited local ownership change context, while ordinary systems commonly require CAP_SYS_ADMIN and fit PR:H. The demonstrated primitive is an invalid use after free read with a possible kernel crash and namespace mapping misclassification, not an OOB write or arbitrary write. Impact is at least local denial of service and limited confidentiality or integrity impact remains plausible but unproven. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 5.8 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage MODERATE to MODERATE_KPANIC because 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 V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 1.5 and ActionableScore 0 with primitive class CLASS_B and manual review REQUIRED. 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_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	READ LEAK UAF HARDWARE LINUS  KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=UNKNOWN
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3.
* Conservative score: 4. REAL UAF FLOOR 4 applied because a live lookup consumes a freed `key_user` field and host-admin-only reachability is not positively established.
* Raw paranoid score: 3.
* Paranoid score: 4. No additional technically supported leverage signal.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 — Real UAF: `keyctl_chown_key()` can replace `keyring->user` and drop the final old `key_user` reference before `find_keyring_by_name()` reads `old_user->uid`.
* +1 — Plausible kernel crash/DoS: KASAN confirms a four-byte slab UAF read.
* +0 — No race penalty: concurrency is required, but the evidence does not establish a materially narrow or unrepeatable race.
* +0 — No privilege penalty: chown is described as privileged, but the exact capability namespace and complete trigger authority are not supplied.
* No controlled reclaim, post-free write, disclosure path, arbitrary access, or protected-state modification is shown.
* No separate availability point is awarded for the same UAF fault.
* B4-PENDING is not established: the stale UID can affect `kuid_has_mapping()`, but no concrete DENY-to-ALLOW execution, below-host-admin complete trigger, or protected resource access is demonstrated.

3. Reachability analysis

A named session-keyring join races a privileged `KEYCTL_CHOWN`. The join side is attacker-invocable, but the evidence does not resolve whether one below-host-admin principal can perform the complete sequence or whether chown requires effective host-administrator power. Namespace-scoped privilege is therefore also unknown. The race is plausibly repeatable, but its practical reliability is not quantified.

4. Primitive and severity reading

This is an active structured-object lifetime violation, not fixed stale storage: the freed `key_user` UID is consumed during named-keyring lookup. The stale operation is a read, not a second release or refcount mutation. The fix avoids the separately-lived account object by reading the keyring’s inline UID.

The primitive is CLASS_B. Proven impact is a slab UAF read and plausible crash; lookup misclassification is possible but no authorization bypass, sensitive key access, confidentiality impact, or integrity change is proven. Consequently, ImportantCandidate is NO and constrained downgrade remains allowed, subject to review of the privilege boundary and downstream lookup behavior.

5. One-sentence report phrase

A concurrent keyring ownership change can free `keyring->user` while named lookup reads its UID, causing a confirmed four-byte slab UAF read and possible kernel crash.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm the exact `KEYCTL_CHOWN` capability scope, whether a below-host-admin actor can drive both sides, and whether stale UID values can produce a material cross-user lookup result.

7. Call-site confidence

Call-site confidence: high

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

Patch: keys: Avoid the owner account dereference in named keyring lookup
Commit: 77249d4b1bb5ad43552b7023c4a0978937aa7a56
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=77249d4b1bb5ad43552b7023c4a0978937aa7a56

Commit description:

Named keyring lookup must keep the storage containing the owner UID
alive through the namespace mapping check.  find_keyring_by_name()
reads keyring->user->uid under keyring_name_lock, but that lock protects
the keyring's name entry and allocation, not its separate key_user.

A named session-keyring join can overlap a privileged KEYCTL_CHOWN on
another CPU.  If the keyring holds the last reference to its old dynamic
key_user and the ownership transfer succeeds, the following ordering is
possible:

    Named join                         Chown
    find_keyring_by_name()              keyctl_chown_key()
      read_lock(keyring_name_lock)       down_write(key->sem)
      load old keyring->user
                                         replace key->user and key->uid
                                         up_write(key->sem)
                                         key_put(key)
                                         key_user_put(old user): free
      read old user->uid
      read_unlock(keyring_name_lock)

Chown neither takes keyring_name_lock nor key_session_mutex, so it can
free the old account between the pointer load and the UID read.  The
lookup then reads freed memory even though the keyring itself is alive.

Use keyring->uid for the mapping check.  key_alloc() initializes this
inline owner UID and keyctl_chown_key() updates it on chown.
The existing name lock keeps its containing keyring allocated throughout
the check, so lookup no longer depends on the account's lifetime.  This
also matches the owner UID used by the permission check.

KASAN report as below:

    BUG: KASAN: slab-use-after-free in find_keyring_by_name+0x577/0x5d0
    Read of size 4 at addr ffff8881128ae2ec by task keycase/500

Cc: stable@vger.kernel.org
Fixes: 2ea190d ("keys: skip keys from another user namespace")
Assisted-by: LLM
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lore.kernel.org/r/pm-key-management-objects-candidate-0002-v3-2baa8cad2bb554364e10@gmail.com
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  security/keys/keyring.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=77249d4b1bb5ad43552b7023c4a0978937aa7a56

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

The original Linux kernel CVE announcement for CVE-2026-99226 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99226

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 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: 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).