[CVE-2026-74683][MODERATE REGULAR] Input: evdev - sanitize event type index when fetching event masks

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

CVE: CVE-2026-74683
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Input: evdev - sanitize event type index when fetching event masks
Commit: c79b08d8fa230871a3634e34a66e591ac2d084ef
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c79b08d8fa230871a3634e34a66e591ac2d084ef
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74683
Analysis date: Sat, 22 Aug 2026 15:53:25 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A Spectre v1 style bounds-check bypass in evdev mask ioctls may allow a local user with access to an input event device to infer limited kernel data through a speculative side channel, with no evidence of memory corruption, crash, or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-74683 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74683

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: NO

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-2026-74683	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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:N/A:N';CWE-203;CWE-125;CWE-208;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.7';DESCR 'A Spectre v1 style information leak may exist in evdev mask ioctls because a user supplied event type for EVIOCGMASK / EVIOCSMASK can be mispredicted past the architectural EV_CNT bounds check. Speculative execution may use the out of bounds type to read the counts array and influence later mask handling, creating a possible kernel data disclosure side channel. For the CVSS the PR:L is used because an attacker needs local code execution and access to an evdev device file, but does not necessarily need full administrator privileges on desktop or delegated input access setups. The issue is not network reachable and does not provide a direct write primitive, UAF, or crash path. Impact is confidentiality only. The base score keeps C:L due to the limited and side channel based primitive, while the paranoid score uses C:H to avoid missing a potentially stronger kernel information disclosure during manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	WRITE OOB SIMPLEFIX HARDWARE LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2

## 1. ActionableScore

* Conservative score: **2**
* Paranoid score: **2**
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

* **Local unprivileged trigger: +1**
  The path is reachable through local `EVIOCGMASK` / `EVIOCSMASK` ioctls on evdev device files, assuming the attacker has access to `/dev/input/event*`.

* **Confidentiality impact plausible: +1**
  The patch addresses a Spectre v1 style speculative out-of-bounds load. This supports a possible side-channel information leak, but not integrity or availability impact.

* **Broad/default/common subsystem: +1**
  `evdev` is a common Linux input subsystem path, especially on desktops and systems exposing input devices.

* **Hard or unreliable exploitation / special side-channel conditions: -1**
  Exploitation depends on speculative execution behavior, misprediction, timing measurement, and a usable side channel. This is not a direct architectural OOB read primitive.

No memory corruption, UAF, OOB write, crash, privilege escalation, network reachability, or shared page corruption primitive is supported by the patch.

## 3. Reachability analysis

A local process with access to an evdev device node may be able to trigger the affected ioctl path. This usually requires being the active desktop user, being in an input-related group, or receiving access through logind or device ACLs. Containers normally do not get access to host input device nodes unless explicitly passed through. The bug is not network reachable and does not affect packet processing. The subsystem is common, but practical exploitation requires local execution plus a viable microarchitectural side channel.

## 4. Severity interpretation

This behaves like an **ordinary Moderate / Low-like local information disclosure issue**, not an Important-class vulnerability. The theoretical issue is a speculative OOB read side channel, but the patch does not show a direct read-back channel, write primitive, memory corruption, kernel crash, or LPE path. The paranoid CVSS confidentiality impact may be raised for manual CVE review sensitivity, but the actionable score remains low because exploitation is local, side-channel dependent, and limited to confidentiality.

## 5. One-sentence report phrase

A Spectre v1 style bounds-check bypass in evdev mask ioctls may allow a local user with access to an input event device to infer limited kernel data through a speculative side channel, with no evidence of memory corruption, crash, or privilege escalation.

## 6. Manual review recommendation

**MANUAL CHECK RECOMMENDED**

Manual review is recommended because this is a kernel information-disclosure class issue involving speculative execution and local device access policy, but it does not currently justify Important handling without additional evidence of a practical disclosure channel or stronger primitive.

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

Patch: Input: evdev - sanitize event type index when fetching event masks
Commit: c79b08d8fa230871a3634e34a66e591ac2d084ef
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c79b08d8fa230871a3634e34a66e591ac2d084ef

Commit description:

The user-supplied event type index passed to EVIOCGMASK / EVIOCSMASK
ioctls is used to index the static counts array in evdev_get_mask_cnt()
and client evmasks array in evdev_get_mask().

While the event type is architecturally bounded by EV_CNT, speculative
execution may mispredict bounds checks and perform out-of-bounds loads.

Sanitize the event type index in evdev_get_mask_cnt() branchlessly using
array_index_mask_nospec(). This clamps the index to 0 for safe array
access and forces the returned count to 0 speculatively when the index
is out of bounds.

We do not need additional array_index_nospec() calls in evdev_get_mask()
because evdev_get_mask_cnt() speculatively forces the count (and
resulting xfer_size) to 0 for out-of-bounds types, preventing any
speculative memory access to client evmasks array.

Reported-by: "Wagenaar, C.C.J. (Chris)" <c.c.j.wagenaar@vu.nl>
Cc: stable@vger.kernel.org
Assisted-by: Antigravity:gemini-3.6-flash
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/anFCAfvxwXB5eJF1@google.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/input/evdev.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=c79b08d8fa230871a3634e34a66e591ac2d084ef

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

The original Linux kernel CVE announcement for CVE-2026-74683 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74683

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:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
  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: 2

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).