[CVE-2026-89876][LOW] media: tda18250: fix possible integer overflow

[CVE-2026-89876][LOW] media: tda18250: fix possible integer overflow

[AL-KERNEL]

CVE: CVE-2026-89876
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: media: tda18250: fix possible integer overflow
Commit: cf8e3b3d7d9a6a96f4df6246e2e14b32f58d889e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cf8e3b3d7d9a6a96f4df6246e2e14b32f58d889e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89876
Analysis date: Wed, 16 Sep 2026 07:09:49 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89876 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89876

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-89876	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89876 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:N/I:N/A:H';CWE-190;CWE-682;CWE-758;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A shift related undefined behavior bug exists in tda18250_pll_calc() because exp can be 0 and the code then calculates a left shift using exp minus 1. This is an arithmetic validation issue in a media tuner PLL calculation path rather than a demonstrated memory corruption primitive. For the CVSS the PR:L is used because an attacker would normally need local access to a DVB media device interface or a process able to request tuner configuration. The issue is not network reachable. Impact is primarily availability through incorrect device operation, UBSAN warning, or possible local denial of service on systems using this specific tuner driver.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	SIMPLEFIX HARDWARE LINUS 	NO	NO	checked

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

ActionableScore=1
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1. No floor or cap applied.
* Raw paranoid score: 1
* Paranoid score: 1. No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +1 Limited availability or correctness impact. The patch fixes an arithmetic undefined behavior case where exp can be 0 and the expression 1 << (exp - 1) becomes a negative shift. This may cause incorrect PLL calculation, device malfunction, UBSAN warning, or limited local DoS on systems using this tuner.

Negative or non-awarded signals:

* +0 Real UAF not awarded. No object lifetime violation, stale pointer, double release, or refcount misuse is established.
* +0 Memory corruption not awarded. The patch shows an invalid arithmetic operation, not an OOB access, UAF, arbitrary write, controlled overwrite, or type confusion.
* +0 Reliable kernel crash not awarded. The evidence supports undefined behavior and possible malfunction, but not a demonstrated host-wide panic.
* +0 Confidentiality and integrity not awarded. There is no disclosure path and no unauthorized modification of protected kernel or user data.
* +0 Remote reachability not awarded. The affected code is a local media tuner driver path, not a network data path.
* +0 Strong LPE or weak LPE not awarded. No useful exploitation primitive beyond invalid arithmetic is established.
* +0 Resource exhaustion not awarded. No persistent allocation or reference leak is present.
* No privilege penalty applied. Host-admin-equivalent privilege is not positively established, but below-host-admin reachability is also not fully established from the supplied patch.

3. Reachability analysis

The likely trigger is local interaction with a DVB media frontend using the tda18250 tuner driver, causing tda18250_pll_calc() to process a hardware or register-derived value where exp becomes 0. The supplied evidence does not establish whether an ordinary local user can always reach the complete tuning path on affected systems, because media device node permissions vary by deployment. It also does not establish that host administrator privileges are required.

HostAdminRequired is therefore UNKNOWN. NamespaceScopedPrivilege is UNKNOWN because no namespace-scoped capability path is involved or demonstrated. No network trigger is supported. The issue depends on the specific tuner driver and compatible hardware, but no extra rare-hardware penalty is applied in the numeric score because the scoring rules require concrete evidence before subtracting for niche deployment. No race or timing condition is involved.

4. Primitive and severity interpretation

The exact primitive is an arithmetic validation bug leading to undefined behavior from a negative shift count. This is not an active structured UAF, fixed stale storage UAF, repeated release/refcount operation, RCU lifetime mismatch, authorization bypass, COW violation, or semantic reinterpretation across security domains.

PrimitiveClass is NONE because no meaningful kernel corruption, ownership, lifetime, authorization, or security-boundary primitive is established. The demonstrated consequence is limited availability or device correctness impact. The speculative consequence is a stronger local DoS if the undefined behavior is compiled or instrumented in a way that causes a fatal warning or device failure, but the patch does not support memory corruption or privilege escalation.

ImportantCandidate is NO because there is no concrete Class A or Class B primitive and no unresolved exploitation leverage beyond the arithmetic UB. AutoDowngradeAllowed is YES because the issue is low-actionability, device-specific, non-network, and lacks memory corruption, security-boundary bypass, or meaningful post-lifetime corruption.

5. One-sentence report phrase

A shift related undefined behavior in tda18250_pll_calc() can occur when exp is 0, leading mainly to incorrect tuner PLL calculation or limited local availability impact on systems using this specific media tuner driver.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: no UAF, no OOB access, no authorization bypass, no remote reachability, no demonstrated kernel memory corruption, and no plausible privilege escalation primitive is established by the patch.

7. Call-site confidence

Call-site confidence: medium

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

Patch: media: tda18250: fix possible integer overflow
Commit: cf8e3b3d7d9a6a96f4df6246e2e14b32f58d889e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cf8e3b3d7d9a6a96f4df6246e2e14b32f58d889e

Commit description:

Integer overflow may occur, when variable exp equals to zero. Result
of shift 1 << (exp - 1) may then leads to undefined behavior.

Fixes: 148abd3 ("media: tda18250: support for new silicon tuner")
Cc: stable@vger.kernel.org
Signed-off-by: Ilya Krutskih <devsec@tpz.ru>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/media/tuners/tda18250.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=cf8e3b3d7d9a6a96f4df6246e2e14b32f58d889e

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

The original Linux kernel CVE announcement for CVE-2026-89876 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89876

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  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: unknown
  Paranoid ActionableScore: 1

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).