[CVE-2026-99245][MODERATE 7.0] KEYS: Fix key_reject_and_link() race with keyring restriction

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

CVE: CVE-2026-99245
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: KEYS: Fix key_reject_and_link() race with keyring restriction
Commit: c7956ec99ad0e173720d95de9fa788bb077809f2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c7956ec99ad0e173720d95de9fa788bb077809f2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99245
Analysis date: Tue, 03 Nov 2026 22:10:49 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A local authorized keyctl caller can race restriction installation and link a rejected key into a keyring after its link policy should deny the operation.

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

The original Linux kernel CVE announcement for CVE-2026-99245 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99245

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-99245	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99245 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=MODERATE_KPANIC RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE_KPANIC, Aegis: MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';CWE-362;CWE-367;CWE-863;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '3.6';DESCR 'A TOCTOU race in key_reject_and_link allowed the restrict_link state to be checked before acquiring the keyring semaphore. A concurrent keyring_restrict operation could install a restriction after that check, after which the rejected key could still be linked into the restricted keyring. For the CVSS the PR:L value reflects that local execution and suitable key authorization or keyring access are required. AC:H reflects the need to win the narrow race during restriction installation. The demonstrated primitive is a keyring policy bypass rather than memory corruption. Confidentiality impact is not supported. Integrity impact is limited to an unauthorized key link, while limited availability impact is plausible if a linked negative key affects later key lookup or request results. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 3.6 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. 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. 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. The independent weaker Aegis shadow evaluated CVSS 1.6 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	SIMPLEFIX RACE LEAK IMPROVEONLY LINUS TEST  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=YES
ProtectedResourceImpact=CONFIRMED
B4PendingReview=YES
B4PendingConfirmed=YES

1. ActionableScore

* Raw base score: 4.
* Conservative score: 5. Manual-review safety floor applied: 4 -> 5 for a concrete authorization bypass affecting a restricted keyring.
* Raw paranoid score: 4.
* Paranoid score: 5. Same floor; no additional speculative impact scored.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 Concrete authorization decision bypass: `restrict_link` should deny linking, but the pre-lock check can observe no restriction and later link after `keyring_restrict()` installs one.
* +1 Local below-host-admin trigger: the grounded syscall path is `KEYCTL_REJECT`/`KEYCTL_NEGATE` through `key_reject_and_link()`, raced against `KEYCTL_RESTRICT_KEYRING`; key authorization is required, not host-administrator power.
* +1 Integrity impact: a rejected/negative key can be linked contrary to the keyring’s installed restriction.
* +1 Practical chain: check-before-lock race directly leads to the unauthorized link.
* -1 Hard timing: exploitation requires winning the narrow restriction-installation race.
* No memory corruption, UAF, confidentiality impact, privilege escalation, arbitrary resource access, or additional availability point is shown.

3. Reachability analysis

A local user with suitable key/keyring authorization can invoke the reject/link and restriction operations without host UID 0 or host-admin capabilities. This is permission-based keyring access rather than a namespace capability path. The attacker must coordinate concurrent operations, but no privileged prior setup, special hardware, or boot configuration is identified.

4. Primitive and severity reading

The primitive is a DENY-to-ALLOW keyring-policy race: `restrict_link` is checked outside the semaphore, then the key is linked after a concurrent restriction becomes active. The fix moves the guard under `__key_link_lock()`, preserving the restriction across the decision and link.

This is CLASS_A authorization bypass, not memory corruption. The protected effect is limited but concrete: unauthorized mutation of a restricted keyring. No LPE, sensitive-key disclosure, or host compromise is proven. B4-PENDING is confirmed for the grounded keyctl path, so Important review is required and automatic downgrade is unsafe.

5. One-sentence report phrase

A local authorized keyctl caller can race restriction installation and link a rejected key into a keyring after its link policy should deny the operation.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm product exposure and practical race reliability; the policy bypass is proven, but broader effects of the unauthorized negative-key link are not.

7. Call-site confidence

Call-site confidence: high

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

Patch: KEYS: Fix key_reject_and_link() race with keyring restriction
Commit: c7956ec99ad0e173720d95de9fa788bb077809f2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c7956ec99ad0e173720d95de9fa788bb077809f2

Commit description:

The restrict_link check in key_reject_and_link() is done before taking
the keyring semaphore, racing with a concurrent keyring_restrict()
that installs the restriction while holding the semaphore in write
mode.

Move the check to after __key_link_lock(), so it is done under the
semaphore, matching the pattern used in __key_create_or_update().

Cc: stable@vger.kernel.org
Fixes: 5ac7eac ("KEYS: Add a facility to restrict new links into a keyring")
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Adrian Martinez <adrimg3196@gmail.com>
Link: https://lore.kernel.org/r/CACO1+RT+m==BY+ZPkE+fo536D0qu3wog4xE1dfuXQ56g+=Qv=A@mail.gmail.com
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  security/keys/key.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=c7956ec99ad0e173720d95de9fa788bb077809f2

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

The original Linux kernel CVE announcement for CVE-2026-99245 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99245

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:H/PR:L/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS score: 3.6

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).