[CVE-2026-64245][MODERATE REGULAR] fbdev: modedb: fix a possible UAF in fb_find_mode()

[CVE-2026-64245][MODERATE REGULAR] fbdev: modedb: fix a possible UAF in fb_find_mode()

[AL-KERNEL]

CVE: CVE-2026-64245
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: fbdev: modedb: fix a possible UAF in fb_find_mode()
Commit: c7dc382439f7b019e207055b52e9cec051d42fa9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c7dc382439f7b019e207055b52e9cec051d42fa9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64245
Analysis date: Fri, 24 Jul 2026 12:06:47 -0400
ActionableScore: 4
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended. Not an Important candidate based on current evidence
Manual review required: YES

Summary:
A use after free read in fb_find_mode can occur when name aliases mode_option_buf after it is freed, potentially causing local DoS or incorrect framebuffer mode handling, with no demonstrated privilege escalation primitive.

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

The original Linux kernel CVE announcement for CVE-2026-64245 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64245

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-2026-64245	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:L/I:L/A:H';*CWE-416;CWE-825;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.8';DESCR 'A use after free read can occur in fb_find_mode when mode_option is NULL and name aliases mode_option_buf. The buffer can be freed before later mode matching logic finishes using name, so subsequent string comparisons may access freed kernel memory. For the CVSS the PR:L is used for the paranoid score because a local user path may be possible on systems where framebuffer mode selection is exposed through device or driver configuration, although the typical reliable trigger is more privileged through boot or driver setup. The issue is not network reachable. Impact is at least local denial of service or incorrect mode selection, with limited confidentiality or integrity impact possible only as a cautious UAF triage assumption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended. Not an Important candidate based on current evidence (with actual score 3)	YES	INIT UAF LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended. Not an Important candidate based on current evidence**

## 2. Signal breakdown

Conservative signals:

* Memory corruption, weak or indirect corruption candidate: +1. This is a use after free read of a string pointer, not a demonstrated write primitive.
* Real lifetime corruption: +1. The freed `mode_option_buf` can still be referenced through `name`.
* Requires admin/root or privileged configuration in typical deployments: -2. Reliable triggering appears tied to fbdev mode option setup, boot parameters, or driver initialization paths.
* Availability impact possible: +1. A stale string read may cause a crash, warning, KASAN report, or incorrect mode handling, but the patch does not show a reliable host-wide crash primitive.

Paranoid signals:

* Local unprivileged trigger: +1. A local path may exist on systems where framebuffer mode selection is exposed through device or driver configuration.
* Memory corruption, weak or indirect corruption candidate: +1. UAF exists, but only a freed string read is shown.
* Real lifetime corruption: +1. The patch fixes object lifetime by extending cleanup to function exit.
* Reliable kernel crash or strong DoS concern: +1. Accessing freed memory in kernel string matching can plausibly crash under allocator or debug configurations.
* Weak LPE concern: +0. No attacker-controlled reclaim, overwrite, stale callback, type confusion, or refcount takeover is shown.
* Confidentiality impact: +0. There is no demonstrated read-back or disclosure primitive.
* Integrity impact: +0. Incorrect mode selection is possible, but no security-relevant integrity primitive is shown.

Call-site confidence: medium. The affected function and direct lifetime issue are visible, but practical external callers and user-controlled reachability are not fully shown in the provided patch.

## 3. Reachability analysis

The bug is local and not network reachable. Typical reliable triggering appears to require control over framebuffer mode options through boot parameters, driver setup, or privileged display configuration paths. In ordinary deployments this is closer to PR:H. A paranoid interpretation can use PR:L if a local user can influence framebuffer mode selection through exposed fbdev or driver interfaces. Containers and namespaces usually do not make fbdev mode setup broadly available unless device access is delegated.

## 4. Severity interpretation

This behaves more like a low to borderline Moderate kernel lifetime bug than an Important-class vulnerability. The theoretical concern is real because this is a UAF in kernel code, but the demonstrated primitive is a freed string read during mode matching. There is no evidence of attacker-controlled reclaim, write-after-free, object replacement, callback control, or privilege escalation. It should not be auto-closed without review because UAF bugs can be under-described, but current evidence does not justify Important severity.

## 5. One-sentence report phrase

A use after free read in fb_find_mode can occur when name aliases mode_option_buf after it is freed, potentially causing local DoS or incorrect framebuffer mode handling, with no demonstrated privilege escalation primitive.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the bug class is UAF and the paranoid score reaches the manual-review range, but the visible primitive is limited to a freed string read and does not currently support Important-class escalation.

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

Patch: fbdev: modedb: fix a possible UAF in fb_find_mode()
Commit: c7dc382439f7b019e207055b52e9cec051d42fa9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c7dc382439f7b019e207055b52e9cec051d42fa9

Commit description:

If mode_option is NULL, it is assigned from mode_option_buf:

  if (!mode_option) {
    fb_get_options(NULL, &mode_option_buf);
    mode_option = mode_option_buf;
  }

Later, name is assigned from mode_option:

  const char *name = mode_option;

However, mode_option_buf is freed before name is no longer used:

  kfree(mode_option_buf);

while name is still accessed by:

  if ((name_matches(db[i], name, namelen) ||

Since name aliases mode_option_buf, this may result in a
use-after-free.

Fix this by extending the lifetime of mode_option_buf until the end of the
function by using scope-based resource management for cleanup.

Signed-off-by: Tuo Li <islituo@gmail.com>
Cc: stable@vger.kernel.org # v6.5+
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/video/fbdev/core/modedb.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=c7dc382439f7b019e207055b52e9cec051d42fa9

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

The original Linux kernel CVE announcement for CVE-2026-64245 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64245

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:L/A:L
  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: 1
  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).