* [CVE-2026-98387][LOW] s390/crypto: Fix skcipher_walk return code handling in aes_s390
@ 2026-10-15 10:14 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-15 10:14 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98387
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: s390/crypto: Fix skcipher_walk return code handling in aes_s390
Commit: 89b58645646d1dac34162cc2597f42266bfbf930
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=89b58645646d1dac34162cc2597f42266bfbf930
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98387
Analysis date: Thu, 15 Oct 2026 06:14:58 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98387 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98387
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: LOW
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98387 LOW https://www.kernelcve.org/list/?q=CVE-2026-98387 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=LOW RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (independent Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-252;*CWE-457;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'The s390 AES skcipher implementation can continue processing after skcipher_walk_virt or skcipher_walk_done reports an error. The walk state may then be invalid or incompletely initialized, which can cause incorrect cryptographic processing, an invalid memory access, or a kernel crash. For the CVSS the PR:L value is used because triggering requires a local process or another local kernel consumer to submit a request to the affected crypto implementation. An unprivileged process may potentially reach skcipher algorithms through AF_ALG when that interface and the s390 AES implementation are available. AC:H is used because an attacker must also cause the walker initialization or advance operation to fail and reach the unsafe continuation path. The issue is not directly network reachable. Impact is primarily local denial of service. Limited confidentiality or integrity impact is retained only in the paranoid score because processing may continue with invalid crypto walk state, but no reliable information leak, controlled write, or privilege escalation primitive is established. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.8 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 2.7 and ActionableScore 1 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE SIMPLEFIX HARDWARE LINUS KPANIC_UNSUPPORTED_REMOVED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Weak or indirect corruption candidate. An error from `skcipher_walk_virt()` or `skcipher_walk_done()` can leave the walk state unsuitable for continued processing, yet the old code may consume its lengths and buffer addresses.
* +1 Realistic kernel crash or strong DoS. Continuing into `memcpy()` or CPACF processing with invalid walk state can cause a kernel fault, although the supplied evidence does not establish reliable triggering.
* No local-unprivileged bonus. AF_ALG is a plausible local entry point, but the supplied call path does not prove that an ordinary user can force the relevant walker failure while selecting this implementation.
* No corruption bonus beyond the weak candidate. No confirmed heap OOB write, arbitrary write, controlled target, UAF, stale lifetime operation, or disclosure is established.
* No confidentiality or integrity bonus. Incorrect cryptographic output is possible, but no protected consumer, leaked data, or unauthorized modification is demonstrated.
* No race penalty. This is error-return mishandling, not a timing race.
* No hardware penalty. The implementation is s390-specific, but no physical attacker access is required and architecture specificity alone is insufficient for a penalty.
* B5-R does not apply. There is no confirmed retry-accumulated heap OOB write or later consumption of a confirmed corrupted descriptor.
* B3-PENDING does not apply. No shared-backing or file-backed write is established.
* B4-PENDING does not apply. No authorization decision or mandatory security guard is bypassed.
3. Reachability analysis
The vulnerable functions are reached through kernel skcipher requests using the s390 AES implementation. A local process may potentially reach this implementation through AF_ALG, but the supplied patch does not show the complete AF_ALG call path or establish how an attacker reliably forces `skcipher_walk_virt()` or a later walk advance to fail.
Consequently, below-host-admin triggering is plausible but not positively established, so `HostAdminRequired` and `RequiresHostUID0` remain `UNKNOWN`. No capability or namespace-specific operation is shown, and the complete trigger cannot be classified as namespace scoped. The affected system must use the s390 AES implementation, but the vulnerability does not require physical attacker access. No race or retry timing is involved.
4. Primitive and severity interpretation
The exact primitive is consumption of an invalid or incompletely initialized skcipher walk after an ignored error return. The affected walk can supply lengths and virtual buffer addresses to AES processing, so an invalid memory access or incorrect operation is technically plausible.
This is not a real UAF, repeated release, refcount mutation, confirmed OOB write, or established arbitrary write. The evidence therefore supports `CLASS_C`, not Class A or Class B. The demonstrated root cause primarily supports incorrect behavior and potential kernel DoS. Stronger confidentiality, integrity, or privilege-escalation consequences remain speculative.
`ImportantCandidate=NO` because no independently useful corruption, ownership, lifetime, authorization, or security-boundary primitive is established. `AutoDowngradeAllowed=YES` because the issue can remain in ordinary Moderate triage while the uncertain trigger and failure semantics are reviewed.
5. One-sentence report phrase
Unchecked skcipher walker errors in the s390 AES implementation may cause processing with invalid walk state, resulting in incorrect cryptographic processing or a local kernel crash, but no concrete OOB write, disclosure, or privilege escalation primitive is established.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Review the exact post-error guarantees of `skcipher_walk_virt()` and `skcipher_walk_done()`, plus AF_ALG reachability, to determine whether attacker-controlled requests can produce usable invalid source or destination addresses rather than only an operation failure or crash.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: s390/crypto: Fix skcipher_walk return code handling in aes_s390
Commit: 89b58645646d1dac34162cc2597f42266bfbf930
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=89b58645646d1dac34162cc2597f42266bfbf930
Commit description:
The return codes from skcipher_walk_virt() were not properly checked
before entering the processing loops in ecb_aes_crypt() and ctr_aes_crypt().
If skcipher_walk_virt() fails, the walk structure may be in an undefined
state, and attempting to process data could lead to incorrect behavior
or accessing uninitialized memory.
Add proper return code checking to ensure correct handling of the walk
initialization and walk advance and eventually return to the caller
with that return code.
Fixes: 7988fb2 ("crypto: s390/aes - convert to skcipher API")
Signed-off-by: Harald Freudenberger <[email protected]>
Reviewed-by: Holger Dengler <[email protected]>
Cc: [email protected] # 5.5+
Signed-off-by: Heiko Carstens <[email protected]>
Signed-off-by: Vasily Gorbik <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
arch/s390/crypto/aes_s390.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=89b58645646d1dac34162cc2597f42266bfbf930
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98387 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98387
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:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS score: 5.8
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: unknown
Paranoid ActionableScore: 2
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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