[CVE-2026-68357][MODERATE 7.0] watchdog: pretimeout: Fix UAF in watchdog_unregister_governor() [ Upstream

[CVE-2026-68357][MODERATE 7.0] watchdog: pretimeout: Fix UAF in watchdog_unregister_governor() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-68357
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: watchdog: pretimeout: Fix UAF in watchdog_unregister_governor() [ Upstream
Commit: 2e47b91b9b4020fcc01def14d6b6556d66074cf4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2e47b91b9b4020fcc01def14d6b6556d66074cf4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68357
Analysis date: Mon, 10 Aug 2026 14:53:38 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A UAF in watchdog pretimeout governor unregister can leave `default_gov` and device `wdd->gov` pointers referencing a freed governor object, allowing a privileged local actor to trigger a kernel crash and requiring manual review for possible stale callback reuse impact.

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

The original Linux kernel CVE announcement for CVE-2026-68357 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68357

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
======================================================================

CVE-2026-68357	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-825;*CWE-664;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A use after free can occur in the watchdog pretimeout governor path when the governor being unregistered is also the global default_gov. The unregister path updates watchdog devices that used the removed governor, but without clearing default_gov it can leave new devices and existing wdd gov pointers referencing a freed governor object. For the CVSS the PR:H is used for the paranoid score because reliable triggering normally requires privileged control over watchdog governor unregistration or module unload on the target system. The issue is not network reachable and is a local kernel lifetime bug. Impact is at least denial of service via kernel crash, and in worst case may allow confidentiality or integrity impact because the stale governor pointer can later be dereferenced from watchdog pretimeout handling.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	DANGER UAF HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Triggered signals:

* Generic memory corruption: +2
  The commit explicitly describes use-after-free of the watchdog governor pointer.

* Real lifetime corruption: +1
  `default_gov` may remain as a stale pointer after the governor is unregistered and freed.

* Reliable kernel crash / strong DoS: +1
  Later watchdog pretimeout handling or registration of new watchdog devices may dereference the dangling governor pointer.

* Weak LPE concern in paranoid scoring: +1
  The stale governor object is not only passive data. Watchdog governors can include callback-style behavior, so a stale pointer dereference may have more serious implications than a simple NULL dereference. No attacker-controlled reclaim is shown, so this is not strong LPE evidence.

* Confidentiality impact plausible in paranoid scoring: +1
  Only for the paranoid score, because UAF reuse could theoretically expose or influence kernel object state.

* Integrity impact plausible in paranoid scoring: +1
  Only for the paranoid score, because stale callback/object reuse can theoretically affect kernel control flow or state.

Subtracted signals:

* Requires admin/root/CAP_SYS_MODULE-like control in typical deployments: -2
  Reliable triggering normally requires unregistering a watchdog governor, unloading a module, or otherwise controlling watchdog governor registration. This is typically privileged.

* Rare / difficult-to-reach configuration: -1
  Watchdog pretimeout governor unregister paths are not a broad default attack surface for ordinary local users.

Conservative arithmetic: `+2 +1 +1 -2 -1 = 1`, rounded up to `2` due to explicit kernel UAF and manual triage relevance.
Paranoid arithmetic: `+2 +1 +1 +1 +1 +1 -2 -1 = 4`, rounded up to `5` because the stale object may be used through governor callback paths and should not be auto-closed.

## 3. Reachability analysis

The bug is local and not network reachable. A realistic trigger normally requires privileged control over watchdog governor unregister or module unload, so ordinary unprivileged users usually cannot reach it directly. Namespaces and containers do not obviously reduce the requirement unless a container or service is incorrectly delegated host-level module or watchdog-management privileges. The affected path is also configuration-dependent because it requires watchdog pretimeout governor usage and unregister activity.

Call-site confidence: medium. The patch and commit clearly show the stale `default_gov` lifetime issue, but the full downstream callback paths are not included in the provided diff.

## 4. Severity interpretation

This is not an ordinary low-risk cleanup because the commit explicitly identifies two UAF cases involving a global governor pointer and per-device `wdd->gov` pointers. Realistically, the most likely impact is a privileged local kernel crash during watchdog governor lifecycle operations. Theoretical privilege escalation is weaker because there is no demonstrated attacker-controlled reclaim, overwrite, or reliable object replacement, but the stale governor pointer may later be dereferenced through callback-like paths, so manual review is justified.

This behaves like an Actionable Moderate issue, not a Strong Important candidate under conservative scoring, mainly because triggering is typically PR:H.

## 5. One-sentence report phrase

A UAF in watchdog pretimeout governor unregister can leave `default_gov` and device `wdd->gov` pointers referencing a freed governor object, allowing a privileged local actor to trigger a kernel crash and requiring manual review for possible stale callback reuse impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: explicit kernel UAF with stale global and per-device pointers. Even though triggering is typically privileged, the stale governor object may be dereferenced later and could involve callback-style behavior, so it should not be auto-closed.

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

Patch: watchdog: pretimeout: Fix UAF in watchdog_unregister_governor() [ Upstream
Commit: 2e47b91b9b4020fcc01def14d6b6556d66074cf4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2e47b91b9b4020fcc01def14d6b6556d66074cf4

Changed files:
  drivers/watchdog/watchdog_pretimeout.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=2e47b91b9b4020fcc01def14d6b6556d66074cf4

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

The original Linux kernel CVE announcement for CVE-2026-68357 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68357

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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: 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: NO
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
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).