[CVE-2026-68451][MODERATE 7.0] s390/zcrypt: Validate length for CCA ECC private key requests

[CVE-2026-68451][MODERATE 7.0] s390/zcrypt: Validate length for CCA ECC private key requests

[AL-KERNEL]

CVE: CVE-2026-68451
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: s390/zcrypt: Validate length for CCA ECC private key requests
Commit: dd25bd9b0f36849808bd7625dcc59dd4c1aeef3e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dd25bd9b0f36849808bd7625dcc59dd4c1aeef3e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68451
Analysis date: Thu, 13 Aug 2026 10:59:56 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local user with access to the s390 CCA pkey/zcrypt ECC private key conversion interface may provide an oversized key token length, causing an out-of-bounds write in CPRB parameter block construction and potentially leading to kernel crash or memory corruption.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68451 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68451

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-2026-68451	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;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 's390 zcrypt CCA ECC private key conversion derives a copy length from the key token length field and could copy more data than fits in the CPRB parameter block. A local user or process that can submit CCA ECC private key conversion requests to the zcrypt pkey interface may provide an oversized token length and trigger an out of bounds write in kernel allocated request memory. For the CVSS the PR:L is used for the paranoid score because reliable triggering requires local access to the relevant pkey or zcrypt interface, but not full administrator privileges in deployments where that interface is available to non root users or service accounts. The issue is not network reachable. Impact is at least local denial of service via kernel memory corruption and in worst case may allow confidentiality or integrity impact, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	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	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process that can access the s390 pkey/zcrypt CCA ECC private key conversion interface may submit a crafted key token.
* Constrained kernel buffer overwrite: +1. The copy length is derived from a key-token length field and can exceed the CPRB parameter block space.
* Weak LPE concern: +1. The bug is an OOB write candidate in kernel request memory, but the patch does not show target selection or a demonstrated reclaim/control primitive.
* Reliable kernel crash / strong DoS: +1. Overrunning the parameter block can plausibly corrupt adjacent kernel allocation/request state and crash.
* Privileged kernel/device-management memory corruption path: +1. The corruption occurs in s390 crypto/zcrypt CCA request construction, a trusted device/crypto subsystem.
* Integrity impact plausible: +1. Kernel memory corruption may affect request state or adjacent metadata.
* Physical-only or rare hardware-only condition: -2. Requires s390 with relevant CCA/zcrypt/pkey functionality.

Paranoid additions/interpretation:

* Generic memory corruption, strong primitive: +2 instead of constrained +1. If the copied key-token bytes are sufficiently attacker-influenced and overflow into adjacent kernel memory, this becomes a stronger heap/OOB-write primitive.
* Privilege escalation plausible: +2 instead of weak +1. In the worst defensible case, kernel heap corruption in a privileged crypto path may be usable beyond DoS.
* Confidentiality impact plausible: +1. Only for paranoid scoring, because memory corruption could theoretically expose or influence sensitive crypto/request state.

## 3. Reachability analysis

The bug is local, not network reachable. Triggering requires the ability to submit CCA ECC private key conversion requests through the relevant s390 pkey/zcrypt interface and requires suitable IBM s390 crypto hardware or configuration. This is not a broad default Linux exposure. Containers or service accounts matter if the zcrypt/pkey device or API is delegated into them, because that can make PR effectively low rather than full host root. Realistic exploitation is hardware and configuration dependent, but the affected operation processes user-provided key-token data before constructing a kernel CPRB request.

## 4. Severity interpretation

This is more than an ordinary Moderate because the patch fixes a missing bounds check where a user-controlled token length can exceed a fixed kernel parameter block. Realistically, the most likely impact is local kernel crash or device/request-state corruption on systems exposing the s390 CCA pkey/zcrypt path. The paranoid interpretation reaches Strong Important candidate because the bug class is an OOB write in kernel memory with possible attacker-influenced payload, even though no concrete LPE primitive is demonstrated in the patch.

## 5. One-sentence report phrase

A local user with access to the s390 CCA pkey/zcrypt ECC private key conversion interface may provide an oversized key token length, causing an out-of-bounds write in CPRB parameter block construction and potentially leading to kernel crash or memory corruption.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a kernel OOB-write candidate in a privileged crypto/device path. Even though exposure is limited to s390 CCA/zcrypt deployments, the memory-corruption nature and possible local privilege-escalation concern make it unsuitable for auto-close.

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

Patch: s390/zcrypt: Validate length for CCA ECC private key requests
Commit: dd25bd9b0f36849808bd7625dcc59dd4c1aeef3e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dd25bd9b0f36849808bd7625dcc59dd4c1aeef3e

Commit description:

cca_ecc2protkey() 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: fa6999e ("s390/pkey: support CCA and EP11 secure ECC private keys")
Signed-off-by: Holger Dengler <dengler@linux.ibm.com>
Cc: stable@vger.kernel.org # 5.10+
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=dd25bd9b0f36849808bd7625dcc59dd4c1aeef3e

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

The original Linux kernel CVE announcement for CVE-2026-68451 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68451

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:L/PR:L/UI:N/S:U/C:L/I:L/A:H
  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: 7

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).