[CVE-2026-80580][MODERATE 7.0] fbdev: bound mode sysfs output to the sysfs buffer

[CVE-2026-80580][MODERATE 7.0] fbdev: bound mode sysfs output to the sysfs buffer

[AL-KERNEL]

CVE: CVE-2026-80580
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: fbdev: bound mode sysfs output to the sysfs buffer
Commit: 873a1aa15c313263f2e18b38cf525623cc4fabf6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=873a1aa15c313263f2e18b38cf525623cc4fabf6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80580
Analysis date: Wed, 26 Aug 2026 13:21:05 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A local out-of-bounds write in the fbdev sysfs modes output path can occur when a long modelist causes the offset to advance past the PAGE_SIZE buffer, leading to kernel memory corruption or crash and requiring manual review for possible privilege escalation impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-80580 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80580

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
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CVE-2026-80580	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:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-119;CWE-190;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'An out of bounds write in the fbdev sysfs modes output path can occur because mode_string used snprintf and show_modes accumulated the would be written length instead of the actual bytes written. If the framebuffer modelist is long enough, the offset can move past the PAGE_SIZE sysfs buffer and a later write can target memory beyond that buffer, causing kernel memory corruption or a crash. For the CVSS the PR:L is used for the paranoid score because a local user or process can potentially trigger the show path by reading the sysfs modes attribute, while reliable triggering still depends on a long modelist and an affected fbdev device. The issue is not network reachable. Impact is at least local denial of service via kernel memory corruption and in the worst case may allow confidentiality or integrity impact, so manual review is needed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	PRINTF-TTY SIMPLEFIX HARDWARE LINUS MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. The vulnerable path is a sysfs show handler, and reading fbdev sysfs attributes is commonly available to local users when the framebuffer device exists.
* Constrained kernel buffer overwrite: +1. The bug can advance the write offset past the PAGE_SIZE sysfs buffer, but the payload is mostly formatted mode data and the overwrite target is not directly attacker-selected.
* Reliable kernel crash / strong DoS concern: +1. An out-of-bounds write past a sysfs buffer can realistically crash the kernel if the modelist is long enough.
* Integrity impact plausible: +1. The primitive is a kernel out-of-bounds write, so corruption of adjacent kernel memory is plausible even if not shown as controllable.

Paranoid additional signals:

* Weak LPE concern: +1. The bug is a kernel OOB write reachable from a local read path, so privilege escalation cannot be dismissed without manual review, but no reclaim, arbitrary write, callback control, or target control is demonstrated.
* Confidentiality impact plausible: +1. In the worst defensible interpretation, adjacent kernel memory corruption could affect sensitive state, but there is no direct info leak primitive.

Not awarded:

* Remote reachable: +0. No network trigger is present.
* Strong LPE plausibility: +0. No controlled overwrite, object replacement, UAF reclaim, type confusion, or arbitrary write is shown.
* Dirty-Pipe-like ownership/COW violation: +0. No page-cache, COW, pipe, splice, or shared-page ownership bypass is involved.

## 3. Reachability analysis

A local user can potentially trigger the vulnerable show path by reading the fbdev modes sysfs attribute, assuming an affected framebuffer device is present. Reliable triggering depends on a sufficiently long framebuffer modelist, which is device and driver dependent and may require uncommon display or fbdev state. Containers usually do not improve reachability unless host fbdev sysfs nodes are exposed into the container. The path is not network reachable and is not a common remote attack surface.

Call-site confidence: high. The relevant caller show_modes() is included in the patch and directly accumulates mode_string() return values into the sysfs output offset.

## 4. Severity interpretation

This is more than an ordinary Moderate because the patch fixes a real kernel out-of-bounds write, not just truncation or formatting cleanup. Realistic exploitation is constrained by the need for a long modelist and by limited control over payload and overwrite target, so the conservative score stays below Important. The paranoid score reaches Actionable Moderate because local kernel memory corruption with plausible DoS and possible but unproven LPE impact should not be auto-closed.

## 5. One-sentence report phrase

A local out-of-bounds write in the fbdev sysfs modes output path can occur when a long modelist causes the offset to advance past the PAGE_SIZE buffer, leading to kernel memory corruption or crash and requiring manual review for possible privilege escalation impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

Reason: this is a local kernel OOB write with constrained but real memory corruption potential, and the practical risk depends on fbdev deployment, modelist controllability, and adjacent allocation behavior.

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

Patch: fbdev: bound mode sysfs output to the sysfs buffer
Commit: 873a1aa15c313263f2e18b38cf525623cc4fabf6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=873a1aa15c313263f2e18b38cf525623cc4fabf6

Commit description:

mode_string() uses snprintf() which can return a value larger than the
remaining buffer space. show_modes() accumulates the return value into i
without checking whether i has reached PAGE_SIZE, causing the offset to
advance past the sysfs buffer if the modelist is long enough.

Add a size parameter to mode_string() and use scnprintf() to return
only the bytes actually written. Add an early return when offset
already exceeds the buffer. In show_modes(), stop accumulating once
the buffer is full.

Cc: stable@vger.kernel.org # v7.1+
Signed-off-by: Melbin K Mathew <mlbnkm1@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/video/fbdev/core/fbsysfs.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=873a1aa15c313263f2e18b38cf525623cc4fabf6

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

The original Linux kernel CVE announcement for CVE-2026-80580 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80580

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: 4
  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: 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).