[CVE-2026-89879][MODERATE 7.0] media: s2255: bound JPEG frame size before copying into the buffer

[CVE-2026-89879][MODERATE 7.0] media: s2255: bound JPEG frame size before copying into the buffer

[AL-KERNEL]

CVE: CVE-2026-89879
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: media: s2255: bound JPEG frame size before copying into the buffer
Commit: 32a595dd3e8634544e5cfbc47f906dff3d3c1ef8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=32a595dd3e8634544e5cfbc47f906dff3d3c1ef8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89879
Analysis date: Wed, 16 Sep 2026 07:48:44 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
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-2026-89879 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89879

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-2026-89879	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89879 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;*CWE-20;CWE-195;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.8';DESCR 'A kernel out-of-bounds write exists in the s2255 USB media driver because s2255_fillbuff() copies jpg_size bytes into a vb2 plane without first bounding jpg_size against the destination plane size. The jpg_size value is taken from the JPEG/MJPEG frame header provided by the device, while only the separate payload length was validated. A malicious or malfunctioning Sensoray 2255 compatible USB device can report a negative or oversized JPEG frame size and make memcpy() write past the video buffer. For the CVSS the PR:N is used because the malicious device does not need privileges on the target system once it can present crafted frame metadata. The issue is not network reachable and is best modeled as AV:P because exploitation normally requires physical access to attach a malicious USB device or control over an already attached capture device. Impact is at least denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact due to device controlled kernel memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	USB SIMPLEFIX HARDWARE LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	NO	NO	checked

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

ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 5
* Raw paranoid score: 3
* Paranoid score: 5
* Applied conservative floor: 2 -> 5 because the patch establishes a concrete attacker-influenced kernel out-of-bounds write.
* Applied paranoid floor: 3 -> 5 for the same controlled kernel corruption primitive.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive signals:

* +2: Strong corruption primitive. `jpg_size` is taken from device-supplied frame metadata and is used as the length for `memcpy()` into a vb2 plane without validating it against the destination plane size.
* +1: Reliable kernel crash / strong DoS. Oversized or negative `jpg_size` can become a huge copy length and plausibly crash the kernel.
* +1: Firmware/device-mediated external influence. The malicious or malfunctioning USB device supplies the metadata that controls the vulnerable copy size.

Negative signals:

* -2: Physical/device-specific access is materially required. The attacker normally needs to attach or control a Sensoray 2255 compatible USB capture device or its data stream.

Paranoid-only signal:

* +1: Weak exploitation concern. The primitive is not merely a NULL dereference or warning. It is an oversized kernel `memcpy()` with device-influenced size and likely device-influenced source data, so memory corruption beyond crash is technically plausible.

Important non-awarded signals:

* Controlled reclaim is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated.
* Remote network reachability is not established.
* UAF is not present.
* Confidentiality impact is not independently demonstrated by a disclosure path.
* Integrity impact is represented by the corruption primitive, but no specific protected object overwrite is proven.
* Extra Availability is not awarded because the same crash is already counted.
* No repeated release/refcount operation exists.

3. Reachability analysis

The direct attacker model is a malicious or malfunctioning USB video capture device. The device can provide crafted JPEG/MJPEG frame metadata, including `jpg_size`, which reaches `s2255_fillbuff()`.

Host administrator privilege is not required by the malicious device itself after it is attached and used. However, practical exploitation depends on physical access or control over an already attached compatible device, and likely on the driver being loaded and capture activity occurring.

This is not namespace-scoped. No network trigger is shown. No prior host-admin setup is proven as part of the vulnerability itself, but deployment requires the relevant USB media device and driver path. There is no race requirement.

4. Primitive and severity interpretation

The exact primitive is an out-of-bounds write past a vb2 video buffer caused by an unchecked signed JPEG frame size used as a `memcpy()` length.

This is not a UAF and not a repeated lifetime/refcount bug. The destination is a fixed video buffer, which constrains target selection, but the size is explicitly device-controlled and the copied JPEG/MJPEG data is plausibly device-controlled. That makes it stronger than crash-only invalid state and supports `PrimitiveClass=CLASS_A`.

Demonstrated consequence is kernel memory corruption and likely kernel crash. Speculative consequence is broader corruption that could affect confidentiality or integrity, but controlled object replacement, arbitrary write, and privilege escalation are not demonstrated.

`ImportantCandidate=YES` because a concrete kernel OOB write exists and should not be downgraded solely due to lack of a full exploit chain. `AutoDowngradeAllowed=NO` because automatic closure would discard a real controlled corruption primitive. Operationally this is best treated as actionable moderate at minimum, with Important review justified despite the physical/device-specific attack surface.

5. One-sentence report phrase

A malicious or malfunctioning Sensoray 2255 compatible USB device can provide an oversized or negative JPEG frame size that makes `s2255_fillbuff()` copy past the vb2 video buffer, causing kernel memory corruption and likely DoS, with broader impact requiring manual review.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a concrete device-controlled kernel out-of-bounds write, not merely a warning, resource leak, or crash-only NULL dereference.

7. Call-site confidence

Call-site confidence: high

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

Patch: media: s2255: bound JPEG frame size before copying into the buffer
Commit: 32a595dd3e8634544e5cfbc47f906dff3d3c1ef8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=32a595dd3e8634544e5cfbc47f906dff3d3c1ef8

Commit description:

s2255_fillbuff() memcpy()s vc->jpg_size bytes of a captured JPEG/MJPEG
frame into the vb2 plane.  vc->jpg_size is taken verbatim from the
S2255_MARKER_FRAME header the device sends (pdword[4] in save_frame())
and, unlike the frame payload length just above it, is never bounded:

	payload = le32_to_cpu(pdword[3]);
	if (payload > vc->req_image_size)	/* payload is checked ... */
		return -EINVAL;
	vc->pkt_size = payload;
	vc->jpg_size = le32_to_cpu(pdword[4]);	/* ... jpg_size is not */

A malicious or malfunctioning device can therefore report a jpg_size
larger than the destination vb2 plane, and the memcpy() writes past it.
jpg_size is a signed int, so a value with the top bit set also turns
into a huge length.

Reject a frame whose jpg_size is negative or exceeds the plane size
before copying it.

Fixes: 38f993a ("V4L/DVB (8125): This driver adds support for the Sensoray 2255 devices.")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: HyeongJun An <sammiee5311@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/media/usb/s2255/s2255drv.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=32a595dd3e8634544e5cfbc47f906dff3d3c1ef8

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

The original Linux kernel CVE announcement for CVE-2026-89879 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89879

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:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.8

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: 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: 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).