[CVE-2026-46191][MODERATE REGULAR] fbcon: Avoid OOB font access if console rotation fails [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-46191
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: fbcon: Avoid OOB font access if console rotation fails [ Upstream
Commit: 594973a2e54924d8ba31c9faac669fc1ba6fcb80
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=594973a2e54924d8ba31c9faac669fc1ba6fcb80
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46191
Analysis date: Thu, 28 May 2026 06:28:52 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A failed fbcon rotated font buffer reallocation can leave a too-small old buffer in use, allowing local console output with high character codes to trigger kernel out-of-bounds font access and possible DoS.

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

The original Linux kernel CVE announcement for CVE-2026-46191 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46191

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.

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

CVE-2026-46191	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-787;*CWE-20;CWE-131;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '5.8';DESCR 'fbcon console rotation can leave an old fontbuffer that is too small when reallocation fails, and later printing a high character code on the rotated console can access memory beyond that buffer. A local actor may trigger the visible fault only after a failed rotation allocation and suitable console output, so the race is not remote and depends on memory pressure and fbcon rotation state. For the CVSS the PR:L is used for the paranoid score because a less privileged local user may be able to print to an already rotated console or influence memory pressure, while full control of rotation is commonly administrator only. The issue is not network reachable. Impact is at least local denial of service and may include limited confidentiality or integrity concern from out of bounds font buffer access, but no reliable write primitive or privilege escalation is demonstrated.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)	YES	OOB SIMPLEFIX LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: **2**
* Paranoid score: **4**
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

* **Local unprivileged trigger, paranoid: +1**
  A less privileged local user may be able to print a high character code to an already rotated console or contribute to memory pressure, although changing console rotation itself is usually privileged.

* **Memory corruption, weak or constrained candidate: +1**
  The commit describes an out-of-bounds font buffer access after failed reallocation. This is kernel memory access beyond the intended buffer, but the patch does not show a controlled overwrite primitive.

* **Reliable kernel crash / strong DoS: +1**
  OOB access in fbcon rendering can plausibly crash the kernel or destabilize the console path.

* **Broad/default/common subsystem: +1 paranoid**
  fbcon is a long-standing console subsystem, although console rotation and fbdev usage are more configuration-specific.

* **Hard or unreliable condition: -1**
  The issue depends on console rotation, a failed allocation during font buffer resize, and later output with a sufficiently high character code.

* **Requires admin/root in typical deployments: -1 to -2**
  Conservative scoring treats rotation control as privileged. Paranoid scoring reduces this because local users may still trigger the final output path if the system is already in the vulnerable rotated state.

## 3. Reachability analysis

The bug is local and not network reachable. Realistic triggering requires fbcon console rotation plus allocation failure in `fbcon_rotate_font()`, followed by console output that indexes beyond the too-small old font buffer. In normal systems, configuring console rotation is usually administrator controlled. Containers generally do not get direct fbcon access unless device or console access is explicitly delegated. The practical exploitability is limited by configuration and timing, but the resulting bug class is kernel OOB access.

## 4. Severity interpretation

This is not a simple warning or resource leak. It is a local OOB access in a kernel console rendering path. Realistic impact is most likely DoS, while confidentiality or integrity impact is only weakly plausible because no controlled write or leak channel is demonstrated. This fits **borderline manual review**, not clear Important.

## 5. One-sentence report phrase

A failed fbcon rotated font buffer reallocation can leave a too-small old buffer in use, allowing local console output with high character codes to trigger kernel out-of-bounds font access and possible DoS.

## 6. Manual review recommendation

**MANUAL CHECK RECOMMENDED**

Manual review is justified because the patch fixes kernel OOB access, but the trigger requires a specific fbcon rotation and allocation-failure scenario and no strong privilege escalation primitive is shown.

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

Patch: fbcon: Avoid OOB font access if console rotation fails [ Upstream
Commit: 594973a2e54924d8ba31c9faac669fc1ba6fcb80
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=594973a2e54924d8ba31c9faac669fc1ba6fcb80

Changed files:
  drivers/video/fbdev/core/fbcon_ccw.c
  drivers/video/fbdev/core/fbcon_rotate.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=594973a2e54924d8ba31c9faac669fc1ba6fcb80

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

The original Linux kernel CVE announcement for CVE-2026-46191 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46191

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:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 2
  Paranoid ActionableScore: 4

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).