[CVE-2026-63823][MODERATE 7.0] keys: Pin request_key_auth payload in instantiate paths

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

CVE: CVE-2026-63823
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: keys: Pin request_key_auth payload in instantiate paths
Commit: d8274181b0f28d450b42489723a5ba81042158d7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d8274181b0f28d450b42489723a5ba81042158d7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63823
Analysis date: Sun, 19 Jul 2026 09:37:20 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in Linux key request authorization can allow a local user path to dereference a freed request_key_auth payload during instantiate or reject handling, causing kernel UAF with realistic DoS and plausible but unproven local privilege escalation risk.

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

The original Linux kernel CVE announcement for CVE-2026-63823 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63823

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-2026-63823	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-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in the Linux key request authorization path can let KEYCTL_INSTANTIATE_IOV or key rejection hold a request_key_auth payload pointer while request_key completion revokes and frees the same payload. The sleeping copy of user payload can widen the race window, and later code may dereference rka target_key after the payload has been freed, causing a kernel use-after-free. For the CVSS the PR:L is used for the paranoid score because a local unprivileged user or helper controlled process can interact with keyrings and the keyctl instantiate or reject paths, without requiring full administrator privileges. The issue is not network reachable and requires local code execution. Impact is at least local denial of service via kernel crash and in worst case may allow privilege escalation due to a kernel UAF primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	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: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1. The affected paths are keyctl instantiate or reject operations and request_key authorization handling, which can be reached by local user processes participating in key instantiation.
* Memory corruption, weak race UAF primitive: +1. The patch explicitly documents a use-after-free of request_key_auth after concurrent helper completion, revoke, and destroy.
* Real lifetime corruption: +1. The fix adds refcounting to pin the request_key_auth payload across sleeping instantiate and reject paths.
* Reliable kernel crash or strong DoS: +1. A stale rka pointer can be dereferenced after free, especially at rka->target_key, making kernel crash realistic.
* Broad/default local subsystem exposure: +1. Linux keyrings and request_key are common kernel facilities, not rare hardware-specific code.
* Hard or unreliable race: -1. Triggering depends on a race window widened by a page fault during payload copy, so reliable exploitation requires timing control.

Paranoid-only consideration:

* Weak LPE concern: +1. The UAF object contains security-relevant pointers such as target_key, dest_keyring, and cred. No reclaim or overwrite primitive is shown, so this is not a strong LPE signal, but it is enough to avoid auto-close and require manual review.

## 3. Reachability analysis

A local user or helper-controlled process can plausibly reach the vulnerable path through request_key and KEYCTL_INSTANTIATE_IOV or key rejection. The issue is not network reachable. Namespaces may matter because keyrings are commonly available to local processes and containerized workloads, although exact reachability depends on keyring restrictions and helper configuration. The race requires one side to hold a request_key_auth payload pointer while sleeping on user memory copy and another side to complete, revoke, and free the authorization payload.

Call-site confidence: high. The patch shows both vulnerable call sites in keyctl_instantiate_key_common and keyctl_reject_key, and the lifetime fix in request_key_auth_get and request_key_auth_put.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because the patch documents an explicit kernel UAF in a common local security subsystem. Realistic impact is at least local DoS because stale pointer dereference after free can crash the kernel. Theoretical LPE is plausible enough for manual review, but the patch does not show attacker-controlled reclaim, type confusion, callback control, or arbitrary write, so the conservative score should not treat it as a proven Important exploit.

## 5. One-sentence report phrase

A race in Linux key request authorization can allow a local user path to dereference a freed request_key_auth payload during instantiate or reject handling, causing kernel UAF with realistic DoS and plausible but unproven local privilege escalation risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Explicit kernel UAF plus local unprivileged reachability makes this unsuitable for auto-close, even though the exploitation primitive is race-dependent and no controlled reclaim or write primitive is demonstrated.

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

Patch: keys: Pin request_key_auth payload in instantiate paths
Commit: d8274181b0f28d450b42489723a5ba81042158d7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d8274181b0f28d450b42489723a5ba81042158d7

Commit description:

A: request_key()       B: KEYCTL_INSTANTIATE_IOV
================       =========================

create auth key
store rka in auth key
wait for helper
                       get auth key
                       load rka from auth key
                       copy user payload
                       sleep on #PF

helper completed
detach and free rka
destroy auth key
                       wake up
                       use rka->target_key
                       **USE-AFTER-FREE**

Give request_key_auth payloads a refcount.  Take a payload reference while
authkey->sem stabilizes the payload and revocation state.  Hold that
reference across the instantiate and reject paths.  Drop the auth key
owning reference from revoke and destroy.

[jarkko: Replaced the first two paragraphs of text with an actual
 concurrency scenario.]
Cc: stable@vger.kernel.org # v5.10+
Fixes: b5f545c ("[PATCH] keys: Permit running process to instantiate keys")
Reported-by: Shaomin Chen <eeesssooo020@gmail.com>
Closes: https://lore.kernel.org/r/20260519144403.436694-1-eeesssooo020@gmail.com
Signed-off-by: Shaomin Chen <eeesssooo020@gmail.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  include/keys/request_key_auth-type.h
  security/keys/internal.h
  security/keys/keyctl.c
  security/keys/request_key_auth.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=d8274181b0f28d450b42489723a5ba81042158d7

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

The original Linux kernel CVE announcement for CVE-2026-63823 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63823

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).