[CVE-2026-99221][MODERATE REGULAR] keys/trusted_keys: return immediately after TPM unseal failure

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

CVE: CVE-2026-99221
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: keys/trusted_keys: return immediately after TPM unseal failure
Commit: 4876f09ce222e140a73aad950882b3605440c935
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4876f09ce222e140a73aad950882b3605440c935
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99221
Analysis date: Mon, 02 Nov 2026 22:56:37 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A successful `pcrlock()` can mask a TPM unseal failure, causing trusted-key instantiation to accept invalid or unvalidated key state.

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

The original Linux kernel CVE announcement for CVE-2026-99221 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99221

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-2026-99221	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99221 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	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:L';CWE-390;CWE-755;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'A logic error in trusted_tpm_unseal can mask a TPM unseal failure when a following pcrlock operation succeeds and overwrites the negative return value with zero. This can make trusted key instantiation report success even though the TPM did not successfully recover or validate the key material. For the CVSS the PR:L value is selected because triggering requires a local process with permission to create or load a trusted key in an accessible keyring. The demonstrated impact is limited integrity loss in the trusted key state. A downstream cryptographic consumer may also experience limited availability impact if it accepts and uses the invalid key. There is no supported memory corruption, plaintext key disclosure, direct privilege escalation, or network reachable primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.4 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. 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. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold 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 INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS unavailable and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	SIMPLEFIX LEAK LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_B
RealUAF=NO
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: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; no floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +1 weak/indirect security-state corruption: a failed TPM unseal can be represented as successful trusted-key instantiation because successful `pcrlock()` overwrites the negative return.
* +1 integrity plausible: the resulting trusted-key state claims success without successful key recovery or validation.
* Paranoid +1 limited availability concern: a downstream cryptographic consumer may fail when using the invalid key state, but no specific consumer or reliable DoS is shown.
* No memory corruption, UAF, disclosure, arbitrary write, LPE, or remote reachability is shown.
* No authorization-bypass score: unseal failure changes operation failure to success, but the evidence does not establish that the failure was specifically a mandatory authorization denial rather than another TPM error.
* No local-unprivileged bonus: the supplied summary says keyring permission is required, but the exact trusted-key capability and credential checks are not visible.

3. Reachability analysis

A local process able to invoke trusted-key creation or loading can reach the operation, with a TPM and `pcrlock` option configured. The evidence does not establish whether the complete trigger requires host administration, numeric UID 0, a delegated keyring permission, or namespace-scoped privilege. No network path, race, unusual timing, or physical attacker access is shown.

4. Primitive and severity reading

The primitive is semantic trusted-key state corruption: an unseal error is lost and failed key material can be accepted as successfully instantiated. This is CLASS_B security-state integrity behavior, not kernel-memory corruption. The patch proves erroneous success reporting; downstream cryptographic failure is plausible but unproven. No protected-resource access or concrete DENY-to-ALLOW authorization path establishes B4-PENDING. Important-grade leverage is therefore not shown, and automatic Moderate handling remains permissible after review.

5. One-sentence report phrase

A successful `pcrlock()` can mask a TPM unseal failure, causing trusted-key instantiation to accept invalid or unvalidated key state.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm trusted-key creation privileges and whether any security-sensitive consumer accepts the unsuccessfully unsealed payload.

7. Call-site confidence

Call-site confidence: medium

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

Patch: keys/trusted_keys: return immediately after TPM unseal failure
Commit: 4876f09ce222e140a73aad950882b3605440c935
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4876f09ce222e140a73aad950882b3605440c935

Commit description:

trusted_tpm_unseal() proceeds to pcrlock() when the TPM unseal operation
fails. If pcrlock() succeeds, its return value overwrites the unseal error,
causing key instantiation to succeed.

Return immediately when unseal fails to preserve the original error.

Cc: stable@vger.kernel.org # v5.15+
Fixes: 5d0682b ("KEYS: trusted: Add generic trusted keys framework")
Signed-off-by: Srish Srinivasan <ssrish@linux.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lore.kernel.org/r/20260912062950.279104-2-ssrish@linux.ibm.com
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  security/keys/trusted-keys/trusted_tpm1.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=4876f09ce222e140a73aad950882b3605440c935

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

The original Linux kernel CVE announcement for CVE-2026-99221 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99221

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: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:L
  The Best / paranoid CVSS score: 4.4

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: 2
  Paranoid ActionableScore: 3

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).