* [CVE-2026-89893][MODERATE REGULAR] media: cx23885: cancel NetUP CI work before teardown
@ 2026-09-16 16:18 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-16 16:18 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89893
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: media: cx23885: cancel NetUP CI work before teardown
Commit: aaf76794b870b0f391eff339252a2e2e22f33a4a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aaf76794b870b0f391eff339252a2e2e22f33a4a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89893
Analysis date: Wed, 16 Sep 2026 12:18:37 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89893 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89893
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-2026-89893 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89893 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:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A workqueue use after free can occur in the cx23885 NetUP CI teardown path because netup_ci_exit frees the CI state while netup_read_ci_status() may still be queued or running. The worker obtains the state via container_of() and dereferences it, so previously queued work can access freed kernel memory after device teardown. For the CVSS the PR:L is used for the paranoid score because a reduced capability admin, service account, or delegated device management path may be sufficient to reach device teardown in some deployments, although typical systems require administrator rights. The issue is not network reachable and requires local interaction with the affected media device or driver lifecycle. Impact is at least denial of service via kernel crash. In the worst case the UAF memory corruption class may allow confidentiality or integrity impact and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) YES DANGER SIMPLEFIX HARDWARE LINUS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 NO NO guess
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_B
RealUAF=YES
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 signals:
* +2 Real UAF / lifetime violation. `netup_ci_exit()` can free `netup_ci_state` while `netup_read_ci_status()` is still queued or running, and the worker later obtains and dereferences the state through `container_of()`.
* +1 Reliable kernel crash / DoS. A workqueue dereference of freed driver state can realistically fault or crash the kernel.
* -1 Narrow teardown / async timing. The stale use depends on queued or running work surviving into CI teardown, which is a teardown ordering window rather than a broad continuously reachable data path.
Paranoid signals:
* +2 Real UAF / lifetime violation.
* +1 Reliable kernel crash / DoS.
* No timing penalty in the paranoid score because the initial status work is queued by init and later CI GPIO interrupts can queue the same work, so the missing `cancel_work_sync()` is a real synchronization defect.
Important non-awarded signals:
* Controlled reclaim is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated.
* Confidentiality and integrity impact are not awarded because the stale path is shown as a dereference of freed driver state, not a disclosure or controlled corruption primitive.
* Structured stale-object exploitation leverage is not awarded because the demonstrated stale use is teardown/workqueue cleanup behavior and no meaningful attacker-shaped replacement object is established.
* Concrete repeated release/refcount mutation is not present. The fix prevents an async worker from using freed state, but it does not show a second `put`, `release`, `kfree`, or refcount mutation on the same dangling reference.
* Extra Availability is not awarded because the same kernel crash is already counted once.
* Remote reachability is not established.
* Local unprivileged trigger is not established.
Repeated-release/refcount check:
* First release can end lifetime: yes, `kfree(state)` ends the lifetime of `netup_ci_state`.
* Exact same reference survives: the work item can still encode access to the freed containing object.
* Second operation is a lifetime/refcount mutation: no, the worker dereferences the stale object but no concrete second lifetime mutation is shown.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.
3. Reachability analysis
The vulnerable condition is reached during the cx23885 NetUP CI teardown path. A software-triggered device remove, driver unload, or equivalent teardown is normally an administrator-controlled operation, but the supplied evidence does not fully prove that host-admin privilege is the only possible trigger in every deployment. Therefore `HostAdminRequired=UNKNOWN`, not `YES` and not `NO`.
The worker can be queued by `netup_ci_init()` and by CI GPIO interrupts via `netup_ci_slot_status()`. `free_irq()` stops future IRQ handlers but does not drain already queued work. This makes the missing synchronization concrete, but it still requires the teardown path to race with pending or running work.
No network trigger is present. No namespace-scoped capability path is indicated. The affected code is for a specific media/DVB PCI device family, so exposure depends on the presence of the cx23885 NetUP CI hardware and driver.
4. Primitive and severity interpretation
The exact primitive is an async workqueue use-after-free of `struct netup_ci_state`. This is a real Class B lifetime bug because a queued worker may access driver state after its lifetime has ended.
The stale storage is closer to fixed driver context than to a broadly attacker-shaped active object. The stale use occurs in a teardown/remove lifecycle path, and the demonstrated consequence is kernel crash or DoS. There is no evidence of controlled reclaim, attacker-controlled replacement contents, callback hijack, arbitrary read/write, information disclosure, or privilege escalation.
This is not Class A because no strong exploitation primitive is established. It is not Class C because the patch directly establishes a real post-lifetime object use rather than only a generic invalid state or warning.
`ImportantCandidate=NO` because the evidence supports a constrained teardown UAF with crash impact, not a strong unresolved exploitation primitive. `AutoDowngradeAllowed=YES` because no concrete repeated lifetime mutation, security-boundary bypass, controlled corruption, or meaningful reuse leverage is shown. Operational severity is best treated as borderline Moderate with manual review recommended due to the real kernel UAF.
5. One-sentence report phrase
A workqueue use-after-free in the cx23885 NetUP CI teardown path can let a pending status worker dereference freed driver state after `netup_ci_exit()`, causing a local kernel crash but with no demonstrated controlled corruption or privilege escalation primitive.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: this is a real kernel UAF, but it appears constrained to a device teardown/workqueue synchronization bug with crash-only demonstrated impact and no concrete stronger exploitation primitive.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: media: cx23885: cancel NetUP CI work before teardown
Commit: aaf76794b870b0f391eff339252a2e2e22f33a4a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aaf76794b870b0f391eff339252a2e2e22f33a4a
Commit description:
netup_ci_exit() frees a netup_ci_state while its work item,
netup_read_ci_status(), may still be pending or running on the system
workqueue. The worker obtains the state with container_of() and
dereferences it, so it must not outlive the state.
netup_ci_init() queues the initial status read, and CI GPIO interrupts
subsequently queue the same work from netup_ci_slot_status(). During
remove, cx23885_finidev() calls free_irq() before the CI device is
unregistered. free_irq() prevents further IRQ handlers from running,
but does not drain work queued previously, so the worker can run after
netup_ci_exit() frees the state.
Call cancel_work_sync() before dvb_ca_en50221_release() and kfree().
This issue was found by an in-house static analysis tool.
Fixes: c184dcd ("V4L/DVB (10798): Add CIMax(R) SP2 Common Interface code for NetUP Dual DVB-S2 CI card")
Cc: [email protected]
Assisted-by: Codex:gpt-5.6
Signed-off-by: Fan Wu <[email protected]>
Signed-off-by: Hans Verkuil <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/media/pci/cx23885/cimax2.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=aaf76794b870b0f391eff339252a2e2e22f33a4a
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89893 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89893
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:N/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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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