[CVE-2026-63824][IMPORTANT] KEYS: fix overflow in keyctl_pkey_params_get_2()

[CVE-2026-63824][IMPORTANT] KEYS: fix overflow in keyctl_pkey_params_get_2()

[AL-KERNEL]

CVE: CVE-2026-63824
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: KEYS: fix overflow in keyctl_pkey_params_get_2()
Commit: 622ec2dcd59f21623f2a7ab773c80ceb7d555e3a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=622ec2dcd59f21623f2a7ab773c80ceb7d555e3a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63824
Analysis date: Sun, 19 Jul 2026 09:39:50 -0400
ActionableScore: 8
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local kernel heap buffer overflow in the KEYS pkey path can occur when caller supplied output length causes an undersized internal buffer allocation, leading to kernel memory corruption, DoS, and possible local privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-63824 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63824

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: IMPORTANT
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-2026-63824	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	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:H/A:H';*CWE-787;CWE-131;CWE-122;BEST CVSS score: '7.8';DESCR 'A kernel buffer overflow can occur in the KEYS pkey path because keyctl_pkey_params_get_2 used the caller supplied output length for the internal output buffer instead of the maximum output size of the selected cryptographic primitive. A local user can provide a too small output length for a pkey operation while the crypto backend may still produce output up to max_enc_size max_dec_size or max_sig_size, causing memory corruption in kernel heap memory. For the CVSS the PR:L is used because a local user or local process must invoke the keyctl pkey interface with a usable asymmetric key and crafted parameters. The issue is not network reachable because it is triggered through a local syscall interface. Impact is at least local denial of service via kernel crash and may allow privilege escalation because the primitive is an out of bounds write in kernel memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-63824 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 00d60fd3b93219ea854220f0fd264b86398cbc53 YES  NO NO unknown 	MAYBE	SIMPLEFIX LINUS  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. The bug is reachable through the local `keyctl` pkey interface, assuming the user can access or create a usable asymmetric key.
* Generic memory corruption, strong corruption primitive: +2. The commit explicitly describes an overflow caused by allocating the internal output buffer using caller supplied length instead of primitive maximum output length.
* Weak LPE concern: +1. Kernel heap overflow can plausibly become privilege escalation, but the patch does not demonstrate target selection, reclaim control, or a concrete exploit primitive.
* Reliable kernel crash / strong DoS: +1. A kernel heap overflow in this path can realistically crash the kernel.

Paranoid additions:

* Strong LPE plausibility instead of weak LPE concern: +1 additional. For paranoid triage, a local kernel heap OOB write in a syscall reachable path is treated as a strong Important candidate.
* Confidentiality impact plausible: +1. If the heap corruption is exploitable, privilege escalation or kernel memory misuse could expose sensitive data.
* Integrity impact plausible: +1. If exploitable, the same primitive could modify kernel state or credentials.

Not counted:

* Remote reachable: +0. This is a local syscall path, not network-triggerable.
* Admin/root required: +0. No CAP_SYS_ADMIN or root requirement is evident for the generic keyctl pkey interface, though a usable key is required.
* Rare subsystem penalty: +0. Asymmetric key pkey operations are not as universal as core syscalls, but KEYS is a common kernel facility and this is not a rare hardware-only path.

Call-site confidence: medium. The full callers are not shown, but the commit explicitly states that the internal output buffer length is miscomputed and can overflow.

## 3. Reachability analysis

A local user or local process can potentially trigger the issue through `keyctl` pkey operations with crafted output length parameters. Practical reachability depends on whether the system enables KEYS/asymmetric key support and whether the attacker can access a usable asymmetric key for encrypt, decrypt, sign, or verify operations. Containers may reduce exposure if `keyctl` is blocked by seccomp or keyring access is restricted, but in normal host environments this should be treated as local PR:L. There is no realistic direct network trigger.

## 4. Severity interpretation

This is not an ordinary Moderate resource leak or validation-only cleanup. The patch fixes a concrete kernel heap buffer overflow caused by allocating an internal buffer too small for the cryptographic primitive output. Conservative handling is Actionable Moderate because a concrete memory corruption primitive exists, but exploit control is not fully demonstrated. Paranoid handling is Strong Important candidate because local kernel heap OOB writes have a plausible privilege escalation path and should not be auto-closed.

## 5. One-sentence report phrase

A local kernel heap buffer overflow in the KEYS pkey path can occur when caller supplied output length causes an undersized internal buffer allocation, leading to kernel memory corruption, DoS, and possible local privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: the patch shows a concrete local kernel memory corruption primitive, and even without a demonstrated exploit chain, the bug class is strong enough to require manual review for LPE potential.

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

Patch: KEYS: fix overflow in keyctl_pkey_params_get_2()
Commit: 622ec2dcd59f21623f2a7ab773c80ceb7d555e3a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=622ec2dcd59f21623f2a7ab773c80ceb7d555e3a

Commit description:

The length for the internal output buffer is calculated incorrectly, which
can result overflow when a too small buffer is provided.

Fix the bug by allocating internal output with the size of the maximum
length of the cryptographic primitive instead of caller provided size.

Link: https://lore.kernel.org/keyrings/20260531024914.3712130-1-jarkko@kernel.org/
Cc: stable@vger.kernel.org # v4.20+
Fixes: 00d60fd ("KEYS: Provide keyctls to drive the new key type ops for asymmetric keys [ver #2]")
Reported-by: Alessandro Groppo <ale.grpp@gmail.com>
Tested-by: Alessandro Groppo <ale.grpp@gmail.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  security/keys/keyctl_pkey.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=622ec2dcd59f21623f2a7ab773c80ceb7d555e3a

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

The original Linux kernel CVE announcement for CVE-2026-63824 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63824

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 5
  Paranoid ActionableScore: 8

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).