[CVE-2026-98221][MODERATE REGULAR] KEYS: trusted: Fix tpm2_load_cmd() boundary check

[CVE-2026-98221][MODERATE REGULAR] KEYS: trusted: Fix tpm2_load_cmd() boundary check

[AL-KERNEL]

CVE: CVE-2026-98221
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: KEYS: trusted: Fix tpm2_load_cmd() boundary check
Commit: cc86227fea28aed86c1fb52a884560b4440da198
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cc86227fea28aed86c1fb52a884560b4440da198
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98221
Analysis date: Fri, 09 Oct 2026 08:07:21 -0400
ActionableScore: 1
ActionableScore lower bound: 0
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-2026-98221 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98221

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-98221	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98221 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF (independent 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:L/I:N/A:H';CWE-125;*CWE-20;CWE-130;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '6.1';DESCR 'An incorrect boundary check in the Trusted Keys TPM2 path compares offsets in a decoded key blob against payload blob_len which describes the larger ASN.1 representation. A malformed key can therefore pass validation even when private_len or public_len points beyond the allocated decoded buffer, leading to an out of bounds read in get_unaligned_be16 or later public data processing. For the CVSS the PR:L value is used because triggering requires a local process to submit a crafted Trusted Key blob through the key management interface, while full administrative privileges are not proven to be universally required. The issue is not network reachable through this code path. Impact is at least a possible local denial of service through an invalid kernel memory read, while the paranoid assessment also considers limited confidentiality impact if adjacent kernel data is copied into a TPM command or otherwise becomes observable. No integrity impact is assigned because the available code establishes an out of bounds read but not an out of bounds write or arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	OOB SIMPLEFIX IMPROVEONLY LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=1
ActionableScoreLower=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Conservative signals:

* +0 Limited heap out-of-bounds read. The decoded buffer has size `ctx.priv_len + ctx.pub_len`, but its internal lengths were checked against the potentially larger ASN.1 `payload->blob_len`.
* +0 No confidentiality signal. The patch does not establish that adjacent kernel bytes are returned to userspace or another attacker-visible endpoint.
* +0 No integrity signal. There is no demonstrated heap out-of-bounds write, corrupted descriptor, arbitrary write, or active-state mutation.
* +0 No reachability bonus. Submission of malformed Trusted Key data is evident, but ordinary unprivileged access to the complete operation is not established.
* +0 No privilege penalty. Host-admin-equivalent privilege is also not positively established.

Paranoid signals:

* +1 Possible kernel crash. A crafted internal length can move `get_unaligned_be16()` or subsequent source-data processing beyond the decoded heap allocation. A sufficiently large invalid read may fault, although a reliable panic is not demonstrated.

Important non-awarded signals:

* B5-R does not apply. Requirement 1 fails because no heap out-of-bounds write is established.
* B5-R requirement 2 also fails because there is no retry-accumulated index, offset, or missing retry reset.
* No corrupted operation, descriptor, or pointer is shown as being consumed after an out-of-bounds write.
* No UAF, double release, refcount mutation, controlled reclaim, callback influence, or arbitrary read or write is established.
* No confidentiality point is awarded merely because kernel memory may be read internally.
* No extra Availability point is awarded beyond the paranoid crash signal.
* Remote reachability and privilege escalation are not established.

3. Reachability analysis

The apparent trigger is a locally supplied malformed ASN.1 Trusted Key blob processed through the kernel key-management and TPM2 Trusted Keys path. The attacker can influence decoded key bytes and embedded length fields.

The supplied evidence does not resolve whether the complete load operation is available to an ordinary user, requires keyring-specific permissions, or requires host-admin-equivalent privilege in the affected configuration. Therefore `HostAdminRequired=UNKNOWN`, with neither a local-unprivileged bonus nor an administrative penalty.

No user-namespace-specific capability path is established. TPM availability, Trusted Keys support, and a usable TPM parent are prerequisites. No retry race, special timing, or network trigger is involved.

4. Primitive and severity interpretation

The exact primitive is a heap out-of-bounds read caused by validating offsets against the encoded ASN.1 payload size rather than the smaller decoded allocation size. The first invalid access may occur while reading `public_len`. Later processing may also consume a source pointer and length derived from the incorrectly accepted layout.

This is not a UAF and does not involve stale storage or a repeated lifetime operation. It is classified as `CLASS_C` because the evidence supports invalid-read and possible crash behavior but not an independently useful disclosure, write, ownership, or authorization primitive.

The practical consequence supported by the patch is malformed-state processing with a possible local kernel fault. Disclosure remains speculative because no attacker-visible path for adjacent bytes is shown. Integrity impact and privilege escalation are unsupported.

`ImportantCandidate=NO` because NEW52 B5-R is not established and no Class A or meaningful Class B primitive exists. `AutoDowngradeAllowed=YES` because the remaining primitive is a constrained read-only boundary violation without demonstrated disclosure or post-read corruption. Manual review is still recommended to inspect the omitted TPM command construction and error paths.

5. One-sentence report phrase

An incorrect decoded-buffer length check in the TPM2 Trusted Keys loader permits a crafted ASN.1 key blob to cause a heap out-of-bounds read and possible local kernel crash, but the supplied evidence does not establish an out-of-bounds write, disclosure path, or privilege-escalation primitive.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review the downstream uses of `pub`, `private_len`, and `public_len` to determine whether out-of-bounds bytes can reach an attacker-observable TPM response or whether a reliable kernel fault is possible.

7. Call-site confidence

Call-site confidence: medium

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

Patch: KEYS: trusted: Fix tpm2_load_cmd() boundary check
Commit: cc86227fea28aed86c1fb52a884560b4440da198
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cc86227fea28aed86c1fb52a884560b4440da198

Commit description:

tpm2_load_cmd() does boundary checks against the ASN.1 size i.e.,
payload->blob_len. Address this by passing the decoded blob size to
tpm2_load_cmd(), and use it for the boundary checks.

Cc: stable@vger.kernel.org # v5.13+
Fixes: f221974 ("security: keys: trusted: use ASN.1 TPM2 key format for the blobs")
Reported-by: co+6a581c4284f721d4@bugs.sh
Closes: https://bugs.sh/b/6a581c4284f721d4/
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Tested-by: Srish Srinivasan <ssrish@linux.ibm.com>
Link: https://lore.kernel.org/r/20260901205809.2028454-1-jarkko@kernel.org
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  security/keys/trusted-keys/trusted_tpm2.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=cc86227fea28aed86c1fb52a884560b4440da198

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

The original Linux kernel CVE announcement for CVE-2026-98221 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98221

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:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 6.1

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: 0
  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: 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).