[CVE-2026-80927][MODERATE REGULAR] timekeeping: Check the return value of tk_get_aux_ts64 in __do_adjtimex()

[CVE-2026-80927][MODERATE REGULAR] timekeeping: Check the return value of tk_get_aux_ts64 in __do_adjtimex()

[AL-KERNEL]

CVE: CVE-2026-80927
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: timekeeping: Check the return value of tk_get_aux_ts64 in __do_adjtimex()
Commit: fecf1e37775269ad38c172b468ad4ecc3968aa63
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fecf1e37775269ad38c172b468ad4ecc3968aa63
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80927
Analysis date: Fri, 11 Sep 2026 17:00:47 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
`__do_adjtimex()` may use uninitialized stack data when `tk_get_aux_ts64()` fails during an auxiliary clock race, causing a local userspace-visible information leak without evidence of memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-80927 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80927

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-2026-80927	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80927 CHECK WITH IMPACT FROM ORIG NN LOW	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-457;*CWE-200;CWE-362;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.7';DESCR '__do_adjtimex() could use uninitialized stack data because the return value of tk_get_aux_ts64() was ignored when reading an auxiliary timekeeper clock. A race where the auxiliary clock becomes disabled during tk_get_aux_ts64() and becomes valid again before clock_valid is checked can leave ts uninitialized and later use it in calculations that are indirectly returned to userspace. For the CVSS the PR:L is used because triggering requires a local process reaching the adjtimex() path, while reliable exploitation also depends on the auxiliary clock state race. The issue is not network reachable. Impact is primarily a local information disclosure from kernel stack data, with no concrete evidence of memory corruption, privilege escalation, or denial of service in the shown patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)  SKIP CVE-2026-80927 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	SIMPLEFIX RACE LEAK LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative 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

Conservative positive signals:

* +1 Confidentiality plausible. The commit explicitly says uninitialized stack data may be used in calculations and indirectly leaked to userspace.
* +1 Practical disclosure path. The path is not merely an internal invalid read: `ts` may remain uninitialized, then is consumed after `tk_get_aux_ts64()`, and the result can reach userspace-visible output.

Paranoid additional signal:

* +1 Kernel stack disclosure sensitivity. Even if the leak is indirect and race-dependent, uninitialized kernel stack exposure may reveal sensitive values or kernel addresses and should not be auto-closed without human review.

Non-awarded signals:

* RealUAF not awarded. The patch does not show stale object use, freed object reuse, double release, refcount misuse, or RCU lifetime violation.
* CLASS_A not awarded. The leak is not shown to be a substantial controlled kernel disclosure, arbitrary read, arbitrary write, or LPE primitive.
* Strong LPE not awarded. No memory corruption, privilege escalation path, callback control, controlled reclaim, or authorization bypass is established.
* Reliable crash or Availability not awarded. The described impact is incorrect calculations and information disclosure, not kernel panic or persistent DoS.
* Race penalty not applied. A race window is described, but the supplied evidence does not quantify it as one-shot, extremely narrow, or practically unretryable enough for a concrete negative point.

## 3. Reachability analysis

The vulnerable code is in `__do_adjtimex()` and is reached through local time adjustment or time query paths. A local process can plausibly reach the relevant syscall interface, but the complete trigger also depends on auxiliary clock state changing during `tk_get_aux_ts64()` and becoming valid again before `clock_valid` is checked.

Host-admin-equivalent privilege is not positively established from the supplied patch, but below-host-admin control of the complete auxiliary-clock enable or disable race is also not fully established. Therefore `HostAdminRequired=UNKNOWN`.

There is no network trigger. There is no namespace-specific evidence. No special hardware requirement is proven, although the issue depends on auxiliary timekeeper clock support being active in the environment. Race repeatability is uncertain: repeated syscall attempts may be possible, but reliable control of the auxiliary clock transition is not shown.

## 4. Primitive and severity interpretation

The exact primitive is use of uninitialized stack data in the timekeeping path, followed by an indirect userspace-visible disclosure. This is not an active structured object UAF and not fixed stale storage. It is an uninitialized stack read plus disclosure issue.

Primitive class is `CLASS_C` because the established behavior is an invalid uninitialized-state use with information disclosure, without a corruption, lifetime, ownership, or authorization primitive.

Demonstrated consequence: local information disclosure from kernel stack-derived data.

Speculative consequence: the leaked data could help bypass mitigations if it contains useful kernel addresses or sensitive stack values, but the patch does not establish a controlled or large disclosure.

`ImportantCandidate=NO` because no strong corruption, UAF, authorization bypass, controlled disclosure, or privilege escalation chain is established.

`AutoDowngradeAllowed=YES` because there is no unresolved Class A or strong Class B primitive. However, manual review is still recommended due to kernel stack disclosure.

Likely operational severity: Low to borderline Moderate. It should not be treated as an Important-class kernel memory corruption issue based on the supplied evidence alone.

## 5. One-sentence report phrase

`__do_adjtimex()` may use uninitialized stack data when `tk_get_aux_ts64()` fails during an auxiliary clock race, causing a local userspace-visible information leak without evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: kernel stack information disclosure is security-relevant even though the primitive is limited, race-dependent, and does not show UAF, arbitrary read/write, DoS, or LPE.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: timekeeping: Check the return value of tk_get_aux_ts64 in __do_adjtimex()
Commit: fecf1e37775269ad38c172b468ad4ecc3968aa63
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fecf1e37775269ad38c172b468ad4ecc3968aa63

Commit description:

If the auxiliary clock is disabled during tk_get_aux_ts64() but is enabled
before tks->clock_valid is checked, then uninitialized stackdata will be
used in the calculations and indirectly leaked to userspace.

The same race window also exists after this change and also for the core
timekeeper. But in these cases the only effect would be incorrect
adjustments and this is userspace's responsibility to avoid this.

Fixes: 4eca49d ("timekeeping: Prepare do_adtimex() for auxiliary clocks")
Signed-off-by: Thomas Weißschuh (Schneider Electric) <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260731-timekeeping-aux-adjtimex-return-v1-1-b7fea4692886@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/time/timekeeping.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=fecf1e37775269ad38c172b468ad4ecc3968aa63

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

The original Linux kernel CVE announcement for CVE-2026-80927 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80927

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: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: 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).