[CVE-2026-68452][MODERATE 7.0] s390/zcrypt: Validate length for CCA AES cipher key requests

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

CVE: CVE-2026-68452
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: s390/zcrypt: Validate length for CCA AES cipher key requests
Commit: 406b317ea2b501f6f5eca1264293c9399a73a778
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=406b317ea2b501f6f5eca1264293c9399a73a778
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68452
Analysis date: Thu, 13 Aug 2026 10:52:01 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An unchecked CCA AES key token length in s390/zcrypt can drive an oversized copy into a fixed CPRB parameter block, creating a local kernel memory corruption risk on systems exposing the zcrypt CCA interface.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68452 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68452

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-2026-68452	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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-20;CWE-122;BEST CVSS score: '7.8';DESCR 's390/zcrypt CCA AES key conversion can derive a copy length directly from the key token length field in cca_cipher2protkey(). If a malformed token provides a length larger than the available CPRB parameter block space, later parameter block construction may write beyond the intended buffer and corrupt kernel memory. For the CVSS the PR:L is selected because reliable triggering requires a local user or process that can reach the zcrypt or CCA key conversion interface, but full administrative privileges are not inherently required in the vulnerability model. The issue is not directly network reachable and is limited to systems with the affected s390 zcrypt CCA functionality. Impact may include kernel crash and in the worst case privilege escalation due to kernel memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8)	YES	SIMPLEFIX LINUS  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	guess

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process that can reach the zcrypt or CCA key conversion interface can potentially provide the malformed key token.
* Memory corruption, strong corruption primitive: +2. The patch validates a user influenced key token length before it is used as a copy length into a fixed CPRB parameter block.
* Weak LPE concern: +1. The primitive is an out of bounds write candidate in kernel memory, but the patch does not show a controlled target, reclaim primitive, callback control, or full arbitrary write.
* Privileged kernel/device-management memory corruption path: +1. The corruption occurs inside a trusted s390 crypto driver path that prepares requests for CCA hardware.
* Integrity impact plausible: +1. Kernel memory corruption can plausibly alter kernel or driver state.
* Availability impact realistic: +1. The same corruption can plausibly crash the kernel or break the zcrypt path.
* Rare hardware/configuration dependency: -1. Exposure is limited to s390 systems with affected zcrypt CCA AES functionality and accessible device/API permissions.

Paranoid differences:

* Privilege escalation plausible upgraded to strong: +2 instead of +1. A user controlled length and likely user controlled token data feeding an oversized kernel copy is enough to justify Important-class manual review.
* Confidentiality impact plausible: +1. In worst case kernel memory corruption could support broader compromise, although no direct info leak is demonstrated.

## 3. Reachability analysis

The issue is local, not network reachable. Triggering requires access to the s390 zcrypt CCA key conversion path, likely through zcrypt/pkey related interfaces or a kernel consumer that accepts CCA AES cipher key tokens. It is not a default exposure on ordinary Linux systems because it depends on s390 architecture and CCA/zcrypt hardware and configuration. Containers do not normally gain access unless the relevant device node or API is delegated into the container. If the device is restricted to root or a trusted group, practical reachability is reduced, but the bug should not be treated as full host-root-only by default because device access can be delegated.

Call-site confidence: medium. The patch snippet does not show the later copy site, but the commit message explicitly states that cca_cipher2protkey derives the copy length for the CPRB parameter block from the token length field.

## 4. Severity interpretation

This behaves like an actionable memory corruption issue, not an ordinary Moderate correctness fix. The conservative view is Actionable Moderate because the affected path is rare and hardware-specific, and the exact overwrite target/control is not shown. The paranoid view is a Strong Important candidate because the patch prevents an oversized copy into a kernel parameter block based on attacker-controlled token length, which is a credible local kernel memory corruption primitive with possible privilege escalation.

## 5. One-sentence report phrase

An unchecked CCA AES key token length in s390/zcrypt can drive an oversized copy into a fixed CPRB parameter block, creating a local kernel memory corruption risk on systems exposing the zcrypt CCA interface.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

This is a kernel memory corruption candidate with local privilege escalation potential, even though practical exposure is limited by s390 zcrypt CCA hardware and device/API permissions.

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UPSTREAM PATCH SUMMARY
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Patch: s390/zcrypt: Validate length for CCA AES cipher key requests
Commit: 406b317ea2b501f6f5eca1264293c9399a73a778
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=406b317ea2b501f6f5eca1264293c9399a73a778

Commit description:

cca_cipher2protkey() derives the copy length for the CPRB parameter
block directly from the length field in the key token. Reject the
request early if the token length exceeds the available space in the
parameter block.

Fixes: 4bc123b ("s390/zcrypt: Add low level functions for CCA AES cipher keys")
Signed-off-by: Holger Dengler <dengler@linux.ibm.com>
Cc: stable@vger.kernel.org # 5.4+
Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/s390/crypto/zcrypt_ccamisc.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=406b317ea2b501f6f5eca1264293c9399a73a778

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

The original Linux kernel CVE announcement for CVE-2026-68452 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68452

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: 6
  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: 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).