* [CVE-2026-98845][MODERATE 7.0] tpm: Disable TPM on null key name mismatch
@ 2026-10-24 0:35 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 0:35 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98845
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: tpm: Disable TPM on null key name mismatch
Commit: a03d0c64cd827a622578623a78defd66b6593b82
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a03d0c64cd827a622578623a78defd66b6593b82
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98845
Analysis date: Fri, 23 Oct 2026 20:35:54 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A TPM2 null-key integrity mismatch can incorrectly return success and pass an uninitialized stack value as the salt-key handle for a subsequent authorization session while the compromised TPM remains enabled.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98845 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98845
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-2026-98845 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98845 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME (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:H/A:H';*CWE-457;CWE-390;CWE-693;CWE-354;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '6.5';DESCR 'A TPM2 null key name mismatch can be detected after TPM interference or reset, but tpm2_load_null returns success without initializing the null key handle. The caller can then use an uninitialized stack value as the salt key handle for TPM2_CC_START_AUTH_SESS while the TPM remains enabled and continues serving requests. This is a logic and uninitialized value flaw rather than a demonstrated kernel memory corruption primitive. It can undermine reset attack protection and may cause failed or incorrectly bound TPM authorization sessions, with possible integrity, confidentiality, and availability impact for TPM backed operations. For the CVSS the PR:L value in the paranoid score represents a reduced privilege local service or user with delegated TPM access and enough platform control to provoke the mismatch. Reliable triggering normally requires a specific TPM reset or interference condition, so AC:H is appropriate. The issue is not directly network reachable. The realistic base impact is limited, but the TPM trust boundary and use of an uninitialized handle justify manual review. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 6.5 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 2.7 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. 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 WARNONLY ERRORPATH HARDWARE LINUS TEST KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK - - checked
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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=UNRESOLVED
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap was applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +1 Weak indirect active-state corruption. `tpm2_load_null()` returns success without initializing `null_key`, and the resulting stack value is consumed as a TPM key handle.
* +1 Security-policy bypass. The null-key name check detects possible TPM reset interference, but the vulnerable path fails open and leaves the TPM operational.
* +1 Concrete corrupted-state consumption chain. The false success reaches `tpm2_start_auth_session()`, which uses the uninitialized value in `TPM2_CC_START_AUTH_SESS`.
* +1 Integrity impact is plausible. An authentication session may be started using an invalid or unintended salt-key handle after the TPM trust check has failed.
Paranoid-only signal:
* +1 V33 active-state and trust-boundary concern. Attacker-influenced TPM state is consumed by a privileged kernel TPM-session path, while delegated TPM, vTPM, and platform-control boundaries remain unresolved.
Not awarded:
* No UAF, OOB access, arbitrary write, controlled reclaim, or kernel-memory corruption is established.
* No reliable kernel crash, information disclosure, privilege escalation, or protected-key compromise is demonstrated.
* No local-unprivileged or remote-reachability bonus was awarded because the complete reset or interference trigger is unresolved.
* No host-admin penalty was applied because host-admin-equivalent privilege is not positively established.
* NEW52 B5-R and NEW53 B3-PENDING do not apply.
* NEW54 B4-PENDING does not apply because this is an integrity and fail-closed check, not a demonstrated authorization DENY-to-ALLOW decision.
3. Reachability analysis
The tested sequence uses QEMU, `swtpm`, and `CONFIG_TCG_TPM2_HMAC=y`, with forced `TPM2_RC_INTEGRITY` and a changed recreated null-key name. This establishes the vulnerable state transition and downstream consumption, but not which real-world attacker can produce the complete sequence.
Ordinary access to a TPM character device does not by itself prove control over TPM reset, context replacement, or null-key recreation. A malicious or controlled vTPM backend, platform-management component, firmware path, or actor with delegated TPM control is credible, but the supplied evidence does not establish that an ordinary local user can perform the complete trigger. Therefore `HostAdminRequired=UNKNOWN`.
The TPM is a host-global device and the relevant reset and session state are not user-namespace or network-namespace scoped. No remote network path is established. This is not a race, and no timing penalty applies.
4. Primitive and severity interpretation
The exact primitive is false success after a failed TPM integrity check, followed by consumption of an uninitialized stack value as an active TPM key handle. The affected state is an active structured resource identifier used by a privileged downstream TPM authorization-session operation.
This is `CLASS_B` because it combines corrupted-state consumption with a fail-open TPM trust-boundary condition. It is not `CLASS_A` because there is no arbitrary kernel write, controlled object replacement, protected-key disclosure, authorization bypass, or demonstrated privilege escalation.
The demonstrated consequence is continued TPM command processing and attempted session creation after a null-key integrity mismatch. Failed session creation or incorrectly selected TPM objects are plausible. Compromise of protected keys, host privileges, or kernel memory remains unproven.
`ImportantCandidate=YES` preserves the V33 trust-boundary candidate for review. `AutoDowngradeAllowed=NO` because automatic closure would discard the unresolved security effect of continuing cryptographic operations after a reset-attack detector has fired and of consuming an uninitialized handle in the authorization-session path.
5. One-sentence report phrase
A TPM2 null-key integrity mismatch can incorrectly return success and pass an uninitialized stack value as the salt-key handle for a subsequent authorization session while the compromised TPM remains enabled.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The TPM reset-attack protection fails open, and uninitialized active state reaches a privileged cryptographic-session consumer, but the attacker privilege boundary and effect on protected TPM resources remain unresolved.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: tpm: Disable TPM on null key name mismatch
Commit: a03d0c64cd827a622578623a78defd66b6593b82
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a03d0c64cd827a622578623a78defd66b6593b82
Commit description:
The null key name check exists to protect against TPM reset attacks, so
a mismatch should stop the device from serving further requests.
Currently it does not disable the chip when it finds a mismatch.
The mismatch is logged:
tpm tpm0: null key integrity check failed
but the chip keeps serving commands:
/ # tpm2_getcap -c properties-fixed
TPM_PT_FAMILY_INDICATOR:
as UINT32: 0x08322e3000
as string: "2.0"
...
tpm2_load_null() where the null key name check is run sets the chip as
disabled only if the rc is non zero. When the mismatch is seen, rc is
zero at that point and it returns success. The other issue is that the
caller expects the null key handle to be populated when the function
returns 0 which it does here without writing the handle and proceeds
assuming the null key handle is valid.
During the test, I noticed that tpm2_start_auth_session() uses the
uninitialized stack value as the key handle since tpm2_load_null()
returns 0 despite the integrity failure and proceeds with
TPM2_CC_START_AUTH_SESS with this value as salt key handle.
Set rc to -ENODEV on the mismatch. The error path then disables the chip
and returns the correct code to the caller.
Tested in QEMU with swtpm and CONFIG_TCG_TPM2_HMAC=y by making
TPM2_CC_CONTEXT_LOAD fail with TPM2_RC_INTEGRITY and changing the name
of the re-created null key. The chip is now disabled on the mismatch.
Fixes: cc7d859 ("tpm: Rollback tpm2_load_null()")
Fixes: 423893f ("tpm: Disable TPM on tpm2_create_primary() failure")
Cc: [email protected] # v6.12+
Assisted-by: LLM
Signed-off-by: Surendran Kanagaraj <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Gunnar Kudrjavets <[email protected]>
Reviewed-by: Jarkko Sakkinen <[email protected]>
Signed-off-by: Jarkko Sakkinen <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/char/tpm/tpm2-sessions.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=a03d0c64cd827a622578623a78defd66b6593b82
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98845 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98845
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:L/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:H
The Best / paranoid CVSS score: 6.5
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: 4
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
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please use reply email interface to add additional manual analyses
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And please, please, let me know when you see Lows instead of Importants
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need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is [email protected] (and both
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