[CVE-2026-98205][MODERATE REGULAR] Input: evdev - zero absinfo before partial copy in EVIOCSABS

[CVE-2026-98205][MODERATE REGULAR] Input: evdev - zero absinfo before partial copy in EVIOCSABS

[AL-KERNEL]

CVE: CVE-2026-98205
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Input: evdev - zero absinfo before partial copy in EVIOCSABS
Commit: c0aebb57b73c7d06ad21731099afe119b113c403
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c0aebb57b73c7d06ad21731099afe119b113c403
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98205
Analysis date: Fri, 09 Oct 2026 04:37:31 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98205 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98205

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-2026-98205	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98205 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N';*CWE-457;*CWE-200;CWE-908;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'EVIOCSABS copies only the user selected ioctl size into an uninitialized input_absinfo stack object and then stores the complete object in device state. A caller can use a short ioctl size and retrieve untouched trailing bytes through EVIOCGABS, producing a local kernel stack information disclosure. For the CVSS the PR:L is selected because the attacker needs a local process with access to the affected evdev device, but full administrative control is not inherently required. The issue is not network reachable. The demonstrated impact is confidentiality loss. Repeated calls may expose kernel pointers or other sensitive stack data and could weaken exploit mitigations, although the available code does not show a direct write primitive or standalone privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	DANGER HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative positive signals:

* +1 Confidentiality plausible. A short EVIOCSABS copy leaves bytes from the kernel stack in `input_absinfo`, and EVIOCGABS returns those bytes to userspace.
* +1 Practical disclosure chain. The patch establishes the complete sequence from attacker-controlled ioctl size, through storage in `dev->absinfo[t]`, to userspace read-back.
* Total: 2.

Paranoid additional signal:

* +1 Weak exploitation concern. Repeated direct kernel-stack disclosures may expose kernel pointers or other mitigation-relevant values, although the actual leaked contents and diversity across calls are not established.
* Total: 3.

Not awarded:

* NEW52 B5-R is not established. There is no heap or slab OOB write, no retry-accumulated index, and no later consumption of OOB-corrupted descriptors.
* No OOB write exists. `dev->absinfo[t] = abs` is an in-bounds structure assignment containing uninitialized bytes.
* No UAF, stale lifetime operation, repeated release, refcount mutation, controlled reclaim, arbitrary write, or memory corruption is demonstrated.
* No integrity or availability point was awarded.
* Local unprivileged trigger was not awarded because access to the relevant evdev device is required and the supplied evidence does not establish its permissions for an ordinary user.
* Host-admin penalty was not applied because host-admin-equivalent privilege is not positively established.
* Remote reachability and privilege escalation are not established.

3. Reachability analysis

The caller must run locally and have permission to open the affected evdev device and issue EVIOCSABS and EVIOCGABS ioctls. The ioctl size is directly controlled by that caller, so exploitation is deterministic once device access exists.

Device-node permissions depend on system policy, input groups, seat management, and dynamically assigned ACLs. The supplied evidence does not prove ordinary-user access to the complete operation, but it also does not prove that host administration is required. Therefore, `HostAdminRequired=UNKNOWN`.

The operation is not governed by an attacker-created namespace capability, so `NamespaceScopedPrivilege=NO`. No network path, special hardware timing, race, retry sequence, boot option, or unrelated vulnerability is required. A suitable evdev device and access to its device node are prerequisites.

4. Primitive and severity interpretation

The exact primitive is a bounded disclosure of uninitialized kernel-stack bytes. A partial `copy_from_user()` initializes only the caller-selected prefix of an on-stack `input_absinfo`. The complete structure is then stored in persistent device state and returned through EVIOCGABS.

This is not an OOB access because both the copy length and destination assignment remain within their respective objects. It is not a UAF or active-object lifetime violation. The security-relevant behavior is the externally visible disclosure of stale stack contents.

The issue is classified as constrained CLASS_B rather than CLASS_A because a real kernel disclosure primitive is established, but the leak is small and no substantial secret disclosure, arbitrary kernel read, mitigation bypass, or completed privilege-escalation chain is demonstrated. The practical consequence is local confidentiality loss. Kernel pointer exposure is a plausible paranoid concern, not a demonstrated Important-grade consequence.

`ImportantCandidate=NO` because no strong corruption, authorization bypass, substantial disclosure, or LPE chain is established. `AutoDowngradeAllowed=YES` because the primitive is bounded and there is no unresolved lifetime corruption or controlled write primitive. Operational severity is Borderline Moderate, with manual review useful for determining device permissions and the actual stack contents exposed on affected builds.

5. One-sentence report phrase

A local process with access to an evdev device can use a short EVIOCSABS request and EVIOCGABS read-back to disclose uninitialized kernel-stack bytes, potentially exposing kernel pointers without causing memory corruption.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm affected device-node permissions and inspect generated stack layout to determine whether repeatable disclosures include kernel pointers, canaries, or other sensitive values.

7. Call-site confidence

Call-site confidence: high

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

Patch: Input: evdev - zero absinfo before partial copy in EVIOCSABS
Commit: c0aebb57b73c7d06ad21731099afe119b113c403
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c0aebb57b73c7d06ad21731099afe119b113c403

Commit description:

The EVIOCSABS handler copies at most the user supplied ioctl size into
an uninitialized on-stack struct input_absinfo:

	if (copy_from_user(&abs, p, min_t(size_t,
			size, sizeof(struct input_absinfo))))

The size comes from _IOC_SIZE() of the ioctl command and is therefore
fully controlled by userspace. A short size leaves the trailing part of
the structure holding whatever was on the kernel stack, and the whole
structure is then stored into the device:

	dev->absinfo[t] = abs;

EVIOCGABS hands that back to userspace, disclosing the stale stack
bytes. Only the resolution field is currently cleared, which covers the
legacy struct layout but not an arbitrarily short size.

Zero the structure before the copy so any part not supplied by the
caller reads back as zero. The existing resolution fixup is kept, since
it also handles a size that partially overlaps that field.

Fixes: 448cd16 ("Input: evdev - rearrange ioctl handling")
Cc: stable@vger.kernel.org
Signed-off-by: Iván Ezequiel Rodriguez <ivanrwcm25@gmail.com>
Link: https://patch.msgid.link/20260901130629.24078-2-ivanrwcm25@gmail.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=c0aebb57b73c7d06ad21731099afe119b113c403

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

The original Linux kernel CVE announcement for CVE-2026-98205 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98205

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:L/PR:L/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 5.5

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: 3

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).