[CVE-2026-74567][MODERATE REGULAR] keys: fix out-of-bounds read in keyring_get_key_chunk() [ Upstream

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

CVE: CVE-2026-74567
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: keys: fix out-of-bounds read in keyring_get_key_chunk() [ Upstream
Commit: d1933e03e8c74a018550c31a393b79c4d95bff40
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d1933e03e8c74a018550c31a393b79c4d95bff40
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74567
Analysis date: Sat, 15 Aug 2026 17:52:45 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local unprivileged user may trigger a slab out-of-bounds read in keyring_get_key_chunk() via crafted colliding key descriptions in add_key(2), with limited confidentiality concern and possible local DoS but no demonstrated write or privilege escalation primitive.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74567 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74567

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
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CVE-2026-74567	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:N/A:H';CWE-125;CWE-126;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '5.3';DESCR 'An out-of-bounds read in keyring_get_key_chunk() can occur when description-level key chunks are requested and the code advances past the inline description prefix without validating the full byte offset against desc_len. A local unprivileged user can potentially reach this path through add_key(2) by creating crafted same-type keys whose index chunks collide through the earlier hash, x, type, and domain_tag levels. For the CVSS the PR:L because the attacker needs local user access and the ability to invoke the key management syscall, but no administrative capability is required. AC:H is used because reliable triggering depends on a crafted collision that makes the assoc_array walk reach the vulnerable description-level chunk. Impact is at least an out-of-bounds kernel read and possible local denial of service in KASAN or hardened configurations, with limited confidentiality concern from a potential heap read oracle.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review / Actionable Moderate at minimum (with actual score 4)	YES	READ KASAN OOB SIMPLEFIX LINUS 	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. The path is reachable via unprivileged add_key(2) with crafted same-type keys.
* Confidentiality impact plausible: +1. The bug is a slab out-of-bounds read, so a limited heap read or oracle is plausible, although no direct userspace disclosure primitive is shown.
* Broad/default/common subsystem exposure: +1. The Linux keyrings subsystem is commonly enabled and reachable through ordinary local syscalls.

Paranoid additional signal:

* Availability impact realistic: +1. KASAN reports slab-out-of-bounds read, and hardened or unlucky layouts could turn this into a local kernel crash, but this is not treated as a strong reliable DoS for the conservative score.

Not awarded:

* No strong memory corruption bonus. This is read-only OOB, not OOB write, UAF, double-free, type confusion, or arbitrary write.
* No LPE bonus. The patch does not show attacker-controlled reclaim, overwrite, callback control, refcount takeover, or object replacement.
* No integrity impact. There is no write primitive.

## 3. Reachability analysis

A local unprivileged user can potentially trigger the bug through add_key(2), but reliable reachability requires crafted key pairs whose assoc_array index chunks collide through hash, x, type, and domain_tag before reaching description-level chunks. This makes exploitation more complex than a trivial syscall crash. Namespaces do not materially remove the concern if key creation is available to the user, but product-specific key quota and keyring restrictions may affect practicality. The path is not network reachable.

Call-site confidence: medium-high. The commit message gives the relevant add_key(2) path and KASAN result, but the full assoc_array traversal context is not included.

## 4. Severity interpretation

This behaves like an actionable local Moderate issue rather than a clear Important vulnerability. The theoretical risk is an unprivileged kernel heap OOB read with possible limited confidentiality impact and possible crash in hardened/debug builds. Realistic evidence does not support privilege escalation or arbitrary memory corruption, so the score should not be raised to Important solely from the bug class.

## 5. One-sentence report phrase

A local unprivileged user may trigger a slab out-of-bounds read in keyring_get_key_chunk() via crafted colliding key descriptions in add_key(2), with limited confidentiality concern and possible local DoS but no demonstrated write or privilege escalation primitive.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: this is an unprivileged kernel out-of-bounds read in the security/keys subsystem, and even though the demonstrated primitive is limited, it should not be auto-closed without checking whether keyring lookup behavior can expose adjacent heap data or create a reliable crash path.

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

Patch: keys: fix out-of-bounds read in keyring_get_key_chunk() [ Upstream
Commit: d1933e03e8c74a018550c31a393b79c4d95bff40
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d1933e03e8c74a018550c31a393b79c4d95bff40

Changed files:
  security/keys/keyring.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=d1933e03e8c74a018550c31a393b79c4d95bff40

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

The original Linux kernel CVE announcement for CVE-2026-74567 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74567

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 3
  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).