[CVE-2026-80544][MODERATE 7.0] s390/zcrypt: Improve EP11 CPRB domain handling with ASN.1 parsing

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

CVE: CVE-2026-80544
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: s390/zcrypt: Improve EP11 CPRB domain handling with ASN.1 parsing
Commit: db21b2cf6dd0af5ffd08931e0a9fcda5a0473220
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=db21b2cf6dd0af5ffd08931e0a9fcda5a0473220
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80544
Analysis date: Wed, 26 Aug 2026 14:09:03 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malformed local EP11 CPRB request can make s390 zcrypt update the domain field using fragile struct overlay assumptions instead of validated ASN.1 parsing, creating a constrained kernel buffer corruption risk in a trusted crypto device path.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-80544 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80544

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-2026-80544	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-20;*CWE-787;CWE-119;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'The s390/zcrypt EP11 CPRB path used fragile struct overlay parsing to locate and modify the domain field inside an ASN.1 encoded payload. A malformed local CPRB request could make the driver rely on an assumed payload layout instead of validated ASN.1 tags and lengths, creating a potential out of bounds write or kernel memory corruption condition when the domain value is updated. For the CVSS the PR:L is used because triggering requires local code execution with access to the zcrypt EP11 interface, but not necessarily full administrative control of the host. The issue is not network reachable by itself and applies only on systems with the relevant s390 zcrypt EP11 hardware and device access exposed. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-80544 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	OOB HARDWARE LINUS  INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	-	-	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

* Local unprivileged or low privileged trigger: +1. Triggering appears to require local access to the zcrypt EP11 interface, but not necessarily full host root.
* Constrained kernel buffer overwrite / weak indirect corruption candidate: +1. The old code writes a kernel derived domain value into a location calculated from fragile ASN.1 layout assumptions.
* Privileged kernel/device-management corruption path: +1. The corruption risk is inside s390 crypto device message handling.
* Integrity impact plausible: +1. A malformed CPRB payload can cause the driver to modify the wrong ASN.1 field or offset inside a trusted kernel prepared device message.
* Availability impact realistic: +1 in the paranoid score only. Malformed parsing and invalid writes can plausibly lead to device request failure or kernel/device-side fault, but no direct crash trace is provided.
* Rare hardware / configuration dependent: -1. This requires s390 zcrypt EP11 hardware and exposed device access.

Not awarded:

* No remote/network trigger.
* No strong LPE signal because there is no demonstrated reclaim, object replacement, type confusion, callback control, arbitrary write, or refcount takeover.
* No strong generic memory corruption +2 in the conservative score because the write value is mostly kernel-derived and the target is a constrained CPRB/AP message buffer, not an attacker-selected arbitrary kernel address.

## 3. Reachability analysis

The likely attacker is a local user or local process with access to the zcrypt EP11 interface. Namespace or container impact depends on whether the device node is passed through to the container, but normal containers usually do not expose this hardware interface by default. The path is not network reachable by itself. Realistic exploitation requires s390 systems with EP11 capable crypto hardware, CONFIG_ZCRYPT support, and permissions that allow issuing the relevant request.

Call-site confidence: medium. The changed function and userspace/device context are visible, but the full ioctl and allocation path is not included in the supplied diff.

## 4. Severity interpretation

This is not an ordinary low-risk validation cleanup because the old code performed direct struct-overlay based writes into an ASN.1 encoded payload without validating tags and bounds. However, the demonstrated primitive is still constrained: the patch does not show arbitrary kernel write, UAF, double free, attacker-controlled reclaim, or a clear privilege escalation path. It should be treated as Actionable Moderate at minimum and manually reviewed, mainly because malformed local input may cause a wrong-offset write inside a trusted kernel/device message path.

## 5. One-sentence report phrase

A malformed local EP11 CPRB request can make s390 zcrypt update the domain field using fragile struct overlay assumptions instead of validated ASN.1 parsing, creating a constrained kernel buffer corruption risk in a trusted crypto device path.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

Reason: the patch replaces unsafe struct-overlay parsing and direct writes with explicit ASN.1 bounds validation, which is a corruption-relevant pattern even though the currently supported primitive appears constrained and hardware dependent.

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

Patch: s390/zcrypt: Improve EP11 CPRB domain handling with ASN.1 parsing
Commit: db21b2cf6dd0af5ffd08931e0a9fcda5a0473220
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=db21b2cf6dd0af5ffd08931e0a9fcda5a0473220

Commit description:

The zcrypt_msgtype6_send_ep11_cprb() function uses fragile struct
overlays to access and modify the domain field in the EP11 CPRB
payload, creating maintainability and security concerns:
1. Struct overlay approach (pld_hdr) assumes fixed payload structure
   and doesn't validate the actual ASN.1 encoding.
2. Complex length format detection logic is error-prone and doesn't
   properly validate bounds at each parsing step.
3. Direct struct member access bypasses proper ASN.1 validation.

Fix by replacing struct overlays with explicit ASN.1 parsing that
validates each field (payload tag/length, function tag/length/value,
optional domain tag/length/value) with proper bounds checking at every
step. Add asn1_int_encode() helper function to safely write integer
values with correct endianness conversion. This makes the code
consistent with the validation pattern introduced with the rework of
the xcrb_msg_to_type6_ep11cprb_msgx() function.

Fixes: e2c6d91 ("s390/zcrypt: Rework domain processing within zcrypt device driver")
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Cc: stable@vger.kernel.org # 7.1+
Reviewed-by: Holger Dengler <dengler@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_msgtype6.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=db21b2cf6dd0af5ffd08931e0a9fcda5a0473220

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

The original Linux kernel CVE announcement for CVE-2026-80544 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80544

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: 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: NO
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).