[CVE-2026-89899][MODERATE 7.0] media: cec: disable delayed work before freeing an interrupted transmit

[CVE-2026-89899][MODERATE 7.0] media: cec: disable delayed work before freeing an interrupted transmit

[AL-KERNEL]

CVE: CVE-2026-89899
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: media: cec: disable delayed work before freeing an interrupted transmit
Commit: 9a951931d4b4084acd64fa55fc3672a9da45ddf9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9a951931d4b4084acd64fa55fc3672a9da45ddf9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89899
Analysis date: Wed, 16 Sep 2026 11:02:12 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89899 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89899

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.

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

CVE-2026-89899	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89899 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:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in the CEC transmit path can leave a delayed_work item armed after its containing transmit data object is freed. cec_transmit_msg_fh drops adap lock while waiting in wait_for_completion_killable, and if a signal interrupts the wait, cancel_delayed_work_sync can run before the CEC kthread schedules the reply timeout work. The work can then be scheduled after cancellation and later run cec_wait_timeout on freed memory, making this a use after free candidate rather than a simple warning. For the CVSS the PR:L is used because a local user or process with access to a CEC device node can attempt the transmit and signal interruption path. The issue is not network reachable. Impact is at least local denial of service via kernel crash, and in the paranoid interpretation may include confidentiality or integrity impact due to the pending work using freed kernel memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	LOCK DANGER UAF HARDWARE LINUS SYZBOT KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 5
* Applied conservative floor/cap: Real UAF floor 5 applied because a below-host-admin local CEC user can influence the interrupted transmit lifetime and a delayed work callback may run after the containing object is freed.
* Raw paranoid score: 6
* Paranoid score: 6
* Applied paranoid floor/cap: none.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative positive signals:

* +2 Real UAF / active lifetime violation: `data->work` can be armed after `cancel_delayed_work_sync()` returns, then `data` is freed while delayed work remains pending.
* +1 Reliable kernel crash / strong DoS: active delayed work on freed storage is realistically capable of producing a kernel fault. The supplied evidence shows `ODEBUG: free active object` with `cec_wait_timeout`.
* +1 Local below-host-admin reachability: the trigger is a local CEC transmit path, and supplied context supports PR:L rather than host-admin-only access.
* +1 Attacker-influenced lifetime manipulation: a local caller can issue a blocking transmit and interrupt `wait_for_completion_killable()` with a signal, influencing the free-vs-work scheduling lifetime transition.

Conservative negative signals:

* -1 Hard race / special timing: the failure requires `cancel_delayed_work_sync()` to run before the CEC kthread arms the reply timeout work, which is a timing-sensitive async interleaving.

Paranoid additional signal:

* +1 Structured stale-object exploitation leverage: the stale operation is not only a passive metadata warning. A real delayed work callback, `cec_wait_timeout`, can later execute using the freed transmit data object. This is meaningful active post-lifetime processing, although controlled reclaim is not demonstrated.

Important non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Confidentiality and integrity are not scored as established consequences.
* Concrete repeated release/refcount mutation is not established.
* Extra Availability point not awarded because the same crash/DoS is already counted once.
* Remote reachability not established.
* Namespace-scoped privilege not established or relevant.
* CLASS_A not assigned because there is no demonstrated controlled replacement, callback hijack, arbitrary R/W, or proven LPE.

Repeated release/refcount checklist:

* First release can end lifetime: yes, `data` is freed after the interrupted transmit path.
* Exact same reference survives to second lifetime mutation: no concrete second put/free/refcount operation is shown.
* Second operation is a real lifetime/refcount mutation: no.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: yes, but due active work-after-free surface, not repeated refcount mutation.

3. Reachability analysis

The evaluated attacker is a local user or process with access to a CEC device node and the ability to invoke the blocking transmit path. The attacker can interrupt the wait with a signal, which can cause cleanup to run while the CEC kthread has not yet armed the delayed reply timeout. Host-admin-equivalent privilege is not positively required by the supplied context, so `HostAdminRequired=NO`.

This is not network reachable. It is not a namespace-scoped capability case. No prior privileged network or namespace setup is established. The practical prerequisite is a system with a CEC adapter or exposed CEC device interface. The race is timing-sensitive because the vulnerable ordering depends on cancellation happening before the kthread schedules `data->work`, but repeated local attempts appear plausible.

4. Primitive and severity interpretation

The exact primitive is an async delayed-work lifetime violation: `data` may be freed while its embedded delayed work remains pending and can later run `cec_wait_timeout` on freed memory. This is an active structured object UAF candidate rather than a mere passive warning, because the pending work item represents future kernel execution over storage whose original lifetime has ended.

This is not a concrete repeated release/refcount UAF. It is closer to active async work-after-free than to ordinary cleanup-only stale dereference. Demonstrated consequence is at least local DoS through kernel fault or debug-object detection. Speculative consequence is stronger memory corruption if the freed object is reused before the delayed work executes, but controlled reclaim or attacker-shaped replacement is not established.

Primitive class is CLASS_B. ImportantCandidate is YES because the active delayed work UAF leaves meaningful exploitation leverage unresolved and should not be automatically downgraded as a simple warning. AutoDowngradeAllowed is NO because automatic closure would discard an unresolved active-object lifetime primitive reachable below host admin. Likely operational severity is Actionable Moderate, with Strong Important candidate review justified.

5. One-sentence report phrase

A race in the CEC blocking transmit path can leave reply timeout delayed work armed after its transmit data object is freed, allowing `cec_wait_timeout` to run on freed memory and causing at least a local kernel crash with unresolved UAF exploitation impact.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real active delayed-work use-after-free candidate reachable from a local device interface, with unresolved post-lifetime callback behavior beyond a simple crash-only warning.

7. Call-site confidence

Call-site confidence: medium

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

Patch: media: cec: disable delayed work before freeing an interrupted transmit
Commit: 9a951931d4b4084acd64fa55fc3672a9da45ddf9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9a951931d4b4084acd64fa55fc3672a9da45ddf9

Commit description:

cec_transmit_msg_fh() drops adap->lock to wait for a blocking transmit in
wait_for_completion_killable(). If that wait is interrupted by a signal,
cancel_delayed_work_sync() can run before the CEC kthread arms the reply
timeout via schedule_delayed_work(&data->work) in cec_transmit_done_ts().
The work is then armed after the cancel, and the data is freed with its
delayed_work still pending:

  ODEBUG: free active (active state 0) object: ... hint: cec_wait_timeout

Use disable_delayed_work_sync(): it cancels the work and disables it, so
the later schedule_delayed_work() becomes a no-op and the work cannot be
re-armed. The data is freed right after, so it need not be re-enabled.

Fixes: 490d84f ("media: cec: forgot to cancel delayed work")
Reported-by: syzbot+051024d603432b4ab395@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=051024d603432b4ab395
Suggested-by: Hillf Danton <hdanton@sina.com>
Cc: stable@vger.kernel.org
Signed-off-by: Biren Pandya <birenpandya@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/media/cec/core/cec-adap.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=9a951931d4b4084acd64fa55fc3672a9da45ddf9

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

The original Linux kernel CVE announcement for CVE-2026-89899 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89899

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:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 5
  Paranoid ActionableScore: 6

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
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).