[CVE-2026-64015][MODERATE 7.0] security/keys: fix missed RCU read section on lookup

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

CVE: CVE-2026-64015
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: security/keys: fix missed RCU read section on lookup
Commit: 4c5d407ba3ff7f30561ff73ba1b07ed70c864edc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4c5d407ba3ff7f30561ff73ba1b07ed70c864edc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64015
Analysis date: Sun, 19 Jul 2026 19:19:02 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A missing RCU read-side critical section in `find_key_to_update()` can let persistent key handling race with assoc_array GC and traverse freed keyring lookup state, creating a local UAF candidate with at least DoS impact and possible privilege-escalation concern requiring manual review.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64015 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64015

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 7.0
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-2026-64015	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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:H/A:H';CWE-362;*CWE-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A missing RCU read side critical section in find_key_to_update can let assoc_array_find traverse keyring assoc_array state while concurrent assoc_array_gc removes nodes and frees them after an RCU grace period. Persistent key handling is the relevant path because regular keyring locking can hide the lifetime issue, while the persistent key model can expose the lookup to a stale or freed node. This is an RCU race and use-after-free candidate in the Linux keys subsystem, so impact is at least local denial of service and may include confidentiality or integrity impact if the freed object can be reused in a useful way. For the CVSS the PR:L is used for the paranoid score because a local unprivileged user or local process can normally interact with keyrings, while no network only trigger is indicated. The issue is not directly network reachable. Impact should be reviewed as possible local privilege escalation rather than treated as a simple crash only bug.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	LOCK SIMPLEFIX LINUS  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  Local users can normally interact with Linux keyrings and persistent key paths without full host root privileges.

* Memory corruption, weak/indirect corruption candidate: +1
  The bug is an RCU lifetime violation where `assoc_array_find()` can traverse keyring assoc_array state without the RCU read-side lock while GC may remove and later free nodes.

* Real lifetime corruption: +1
  The missing RCU read section directly affects object lifetime protection and can expose stale or freed assoc_array nodes.

* Reliable kernel crash / strong DoS: +1
  A lookup racing with assoc_array GC can plausibly dereference freed memory and crash the kernel.

* Broad/default/common subsystem: +1
  The Linux keys subsystem is a common in-kernel security-related facility, not a rare driver-only path.

* Hard or unreliable race / special timing required: -1
  The issue depends on a race between persistent key handling lookup and assoc_array GC/free after an RCU grace period.

Paranoid delta: the paranoid score does not subtract the race penalty as strongly because local keyring operations can potentially be repeated and shaped by the attacker. It remains capped at 5 under the race-UAF downgrade rule because the patch does not show attacker-controlled reclaim, write-after-free, callback control, type confusion, or refcount takeover.

## 3. Reachability analysis

A local user or local process is the realistic trigger. No network-only trigger is indicated. Persistent key handling is specifically called out as the exposed model because regular keyring locking can hide the lifetime problem. Namespaces and containers may matter because reduced-capability users or containerized processes may still have access to keyring operations, so treating this as full PR:H would understate practical risk. The path is not a packet-processing or remote protocol path, but it is in a broadly available security subsystem.

Call-site confidence: medium. The patch shows the affected lookup site and the commit explains the assoc_array GC lifetime model, but the full persistent key call chain is not included in the input.

## 4. Severity interpretation

This behaves more like Actionable Moderate than ordinary Moderate. The realistic evidence supports a local race-dependent UAF candidate and possible kernel crash. Theoretical privilege escalation is possible because this is a lifetime bug in security/keys code, but the provided patch does not demonstrate controlled reclaim, object replacement, write primitive, or callback hijack. Therefore the conservative score should not be raised to Important solely from the UAF label, but the issue should not be auto-closed.

## 5. One-sentence report phrase

A missing RCU read-side critical section in `find_key_to_update()` can let persistent key handling race with assoc_array GC and traverse freed keyring lookup state, creating a local UAF candidate with at least DoS impact and possible privilege-escalation concern requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is an RCU lifetime bug and UAF candidate in the Linux keys security subsystem. Even though the exploit primitive is not proven from the patch alone, the subsystem and bug class justify manual review rather than automatic closure.

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

Patch: security/keys: fix missed RCU read section on lookup
Commit: 4c5d407ba3ff7f30561ff73ba1b07ed70c864edc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4c5d407ba3ff7f30561ff73ba1b07ed70c864edc

Commit description:

Nicholas Carlini reports that the keyring code calls assoc_array_find()
in find_key_to_update() without holding the RCU read lock, while the
assoc_array_gc() code really is designed around removing the node from
the tree and then freeing it after an RCU grace-period.

The regular key handling doesn't see this because holding the keyring
semaphore hides any lifetime issues, but the persistent key handling
uses a different model.

Instead of extending the keyring locking, just do the simple RCU locking
that the assoc_array was designed for.

Reported-by: Nicholas Carlini <npc@anthropic.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: James Morris James Morris <jmorris@namei.org>
Cc: Serge E. Hallyn <serge@hallyn.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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=4c5d407ba3ff7f30561ff73ba1b07ed70c864edc

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

The original Linux kernel CVE announcement for CVE-2026-64015 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64015

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:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 4
  Paranoid ActionableScore: 5

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).