[CVE-2026-46283][MODERATE REGULAR] tpm: Use kfree_sensitive() to free auth session in tpm_dev_release()

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

CVE: CVE-2026-46283
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: tpm: Use kfree_sensitive() to free auth session in tpm_dev_release()
Commit: dd3ac52ea7a001406c7dbc663aae4b9f89da679a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dd3ac52ea7a001406c7dbc663aae4b9f89da679a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46283
Analysis date: Mon, 08 Jun 2026 15:50:40 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended, not an Important candidate by itself
Manual review required: YES

Summary:
TPM auth session memory was freed without scrubbing, leaving HMAC keys, nonces, and passphrase related data in freed slab memory until overwritten, with confidentiality impact only if another path can expose that memory.

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

The original Linux kernel CVE announcement for CVE-2026-46283 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46283

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-46283	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N';CWE-226;CWE-212;CWE-244;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.7';DESCR 'TPM auth session memory can retain sensitive HMAC session keys, nonces, and passphrase data because tpm_dev_release() used kfree() instead of a scrubbing free operation for chip auth. This is primarily a sensitive data remanence issue rather than memory corruption, since the patch does not show a direct kernel heap read primitive. For the CVSS the PR:L is used for the paranoid score because a local user or service with TPM access may create or handle auth material, while reliable device teardown usually needs higher administrative control. The issue is not network reachable and does not directly cause DoS or privilege escalation. Impact is confidentiality only, with higher concern if another local path can expose reused or uninitialized slab memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended, not an Important candidate by itself (with actual score 2)  SKIP CVE-2026-46283  SKIP The Fixes patch not applied yet, so unlikely that actual: 699e3efd6c645c741ea4d6d58282c56b6d108cf7 YES  NO NO unknown 	MAYBE	UAF HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended, not an Important candidate by itself**

## 2. Signal breakdown

* Local TPM user influence: +1
  A local user or service with TPM access may create or handle TPM2 HMAC auth session material.

* Confidentiality impact plausible: +1
  The freed object may retain HMAC session keys, nonces, and passphrase related data in slab memory.

* Security-sensitive subsystem and secret material: +1
  TPM auth data is cryptographic material. This justifies manual review even without a direct disclosure primitive.

* No direct memory disclosure primitive: -1
  The patch only changes kfree() to kfree_sensitive(). It does not show a kernel heap read, UAF reclaim, OOB read, or user-visible disclosure path.

* Admin or device lifecycle dependency in conservative interpretation: -2
  The vulnerable free path is tpm_dev_release(), which normally occurs during device teardown or driver lifecycle operations and is not usually controlled by an unprivileged user.

## 3. Reachability analysis

The sensitive data can be created during normal TPM2 HMAC session use, potentially by local users or services allowed to access the TPM device. However, the vulnerable free occurs in the device release path, which typically requires administrative control over device removal, driver unload, or system teardown. Containers and reduced-privilege services may matter if TPM device access is delegated, but they still do not get a direct primitive to read freed slab memory from this patch alone. The path is not network reachable.

## 4. Severity interpretation

This behaves like a low to borderline Moderate confidentiality issue, not like memory corruption or LPE. The theoretical concern is that sensitive TPM auth material remains in freed kernel memory and could be exposed by a separate kernel memory disclosure bug or slab reuse path. Realistically, this patch alone does not provide disclosure, integrity modification, DoS, or privilege escalation.

## 5. One-sentence report phrase

TPM auth session memory was freed without scrubbing, leaving HMAC keys, nonces, and passphrase related data in freed slab memory until overwritten, with confidentiality impact only if another path can expose that memory.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: cryptographic material is involved, but there is no direct read primitive or memory corruption shown by the patch, so this should not be treated as Important without additional evidence.

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

Patch: tpm: Use kfree_sensitive() to free auth session in tpm_dev_release()
Commit: dd3ac52ea7a001406c7dbc663aae4b9f89da679a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dd3ac52ea7a001406c7dbc663aae4b9f89da679a

Commit description:

tpm_dev_release() uses plain kfree() to free chip->auth, which contains
sensitive cryptographic material including HMAC session keys, nonces,
and passphrase data (struct tpm2_auth).

Every other code path that frees this structure uses kfree_sensitive()
to zero the memory before releasing it: both tpm2_end_auth_session()
and tpm_buf_check_hmac_response() do so. The tpm_dev_release() path
is the only one that does not, leaving key material in freed slab
memory until it is eventually overwritten.

Use kfree_sensitive() for consistency with the rest of the driver and
to ensure session keys are scrubbed during device teardown.

Cc: stable@vger.kernel.org # v6.10+
Fixes: 699e3ef ("tpm: Add HMAC session start and end functions")
Signed-off-by: Gunnar Kudrjavets <gunnarku@amazon.com>
Reviewed-by: Justinien Bouron <jbouron@amazon.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/char/tpm/tpm-chip.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=dd3ac52ea7a001406c7dbc663aae4b9f89da679a

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

The original Linux kernel CVE announcement for CVE-2026-46283 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46283

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:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 4.7

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: 1
  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).