[CVE-2026-68453][MODERATE 7.0] s390/zcrypt: Fix buffer over-read in cca_cipher2protkey

[CVE-2026-68453][MODERATE 7.0] s390/zcrypt: Fix buffer over-read in cca_cipher2protkey

[AL-KERNEL]

CVE: CVE-2026-68453
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: s390/zcrypt: Fix buffer over-read in cca_cipher2protkey
Commit: a57fd7fcdb63e2d5ceac78bbe825ec986062a9da
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a57fd7fcdb63e2d5ceac78bbe825ec986062a9da
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68453
Analysis date: Thu, 13 Aug 2026 10:55:52 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malformed user-controlled CCA token supplied through the s390 zcrypt or pkey interface can cause an out-of-bounds kernel buffer read or under-read, potentially leading to kernel crash or memory exposure through the crypto card request path.

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

The original Linux kernel CVE announcement for CVE-2026-68453 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68453

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-2026-68453	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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:N/A:H';CWE-125;CWE-126;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '7.1';DESCR 'The s390 zcrypt CCA token validation path can read outside the supplied key buffer because user controlled token len fields were not consistently checked against the real buffer size and the minimum token structure size. A local attacker with access to the pkey or zcrypt interface may provide a malformed CCA token with an oversized or undersized length field, causing an out-of-bounds read, kernel crash, or possible exposure of adjacent kernel memory through the crypto card request path. For the CVSS the PR:L is used because reliable triggering requires local access to the affected zcrypt or pkey interface but does not necessarily require full administrative privileges on systems where that interface is exposed to a normal service account or user. The issue is not network reachable and applies only to affected s390 systems with the relevant CCA crypto support. Impact is at least local denial of service and in the paranoid case may include high confidentiality impact due to kernel memory over-read.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	OOB DANGER IMPROVEONLY KERNEL_PANIC_PLUS_UAF LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6	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

Conservative signals:

* Local unprivileged trigger: +1. A local user or service with access to the affected pkey or zcrypt interface can supply malformed CCA key tokens.
* Limited read-only OOB memory-safety primitive: +1. The patch fixes user-controlled token length fields causing buffer over-read or under-read.
* Reliable kernel crash / strong DoS: +1. The commit explicitly says the issue may result in a kernel crash.
* Confidentiality impact plausible: +1. The commit explicitly mentions possible exposure of memory via data sent as part of a request to the crypto card.
* Rare / hardware-specific subsystem: -1. This requires s390 zcrypt CCA crypto support and relevant hardware/configuration.
* Privileged kernel/device-management path: +1. The bug is in trusted crypto adapter request preparation and token validation code.

Paranoid additional signal:

* Availability impact realistic: +1. In the paranoid interpretation, the crash is treated as host-wide and practically relevant once the interface is reachable.

Call-site confidence: high. The patch includes both validation helpers and visible callers in pkey_cca.c and zcrypt_ccamisc.c.

## 3. Reachability analysis

The likely attacker is local, not remote. Triggering requires access to the pkey or zcrypt interface on an s390 system with CCA crypto support. This does not appear network reachable by itself.

Typical privilege depends on device node permissions and product configuration. It should not be treated as full PR:H by default because access may be delegated to service accounts or crypto users rather than only full host root. Containers/namespaces usually do not make this broadly reachable unless the relevant device interface is passed through.

The path is not broadly default-exposed across Linux systems because it is architecture and hardware specific, but on affected s390 deployments it is a real local kernel interface.

## 4. Severity interpretation

This is more than an ordinary validation cleanup because the downstream primitive is a kernel buffer over-read or under-read with explicit crash and possible memory exposure. It is not a strong Important candidate by default because the patch does not show an OOB write, UAF, controlled overwrite, type confusion, or direct privilege escalation path.

Realistic impact is local DoS plus possible kernel memory disclosure through the crypto request path. Theoretical LPE is not supported by the patch, so the score should stay in Actionable Moderate rather than Important.

## 5. One-sentence report phrase

A malformed user-controlled CCA token supplied through the s390 zcrypt or pkey interface can cause an out-of-bounds kernel buffer read or under-read, potentially leading to kernel crash or memory exposure through the crypto card request path.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is an OOB read/under-read in a kernel crypto device path with explicit possible memory exposure, so it should not be auto-closed even though it is local and hardware-specific.

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

Patch: s390/zcrypt: Fix buffer over-read in cca_cipher2protkey
Commit: a57fd7fcdb63e2d5ceac78bbe825ec986062a9da
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a57fd7fcdb63e2d5ceac78bbe825ec986062a9da

Commit description:

Add validation of both the actual key buffer size and token length
fields in all the cca_check_sec*token() functions. Additionally check
in cca_gencipherkey() for possible underflow with returned key size.

The CCA token structures contain user-controlled len fields that
were used in operations without proper validation against both the
actual buffer size and minimum token structure size. An attacker
could set this field larger than the actual buffer size, leading to
reading beyond buffer boundaries. This may result in a kernel crash or
exposure of memory via sending this as part of a request down to the
crypto card. Also an attacker could have used a very small len value
and thus enforce a buffer under-run which may produce similar effects
as a over-read.

So now a key must
- key buf length must be at least sizeof the token struct
- the key len field inside the token must fit into the range of
  sizeof key token struct ... key buf length

Fixes: 4bc123b ("s390/zcrypt: Add low level functions for CCA AES cipher keys")
Cc: stable@vger.kernel.org
Reviewed-by: Ingo Franzki <ifranzki@linux.ibm.com>
Signed-off-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/pkey_cca.c
  drivers/s390/crypto/zcrypt_ccamisc.c
  drivers/s390/crypto/zcrypt_ccamisc.h

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=a57fd7fcdb63e2d5ceac78bbe825ec986062a9da

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

The original Linux kernel CVE announcement for CVE-2026-68453 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68453

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:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 7.1

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).