* [CVE-2026-98648][MODERATE REGULAR] s390/uv: Prevent potential out-of-bounds read [ Upstream
@ 2026-10-19 6:15 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-19 6:15 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98648
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: s390/uv: Prevent potential out-of-bounds read [ Upstream
Commit: 04bb5b2eb9f1d56110f14d3a4e31fa2c65fb026f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=04bb5b2eb9f1d56110f14d3a4e31fa2c65fb026f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98648
Analysis date: Mon, 19 Oct 2026 02:15:14 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
An incorrect per-page loop bound in s390 UV secret lookup can read beyond the current secrets array when more than 85 secrets exist, but no direct disclosure, write primitive, privilege escalation, or reliable crash is established.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98648 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98648
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 REGULAR
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-2026-98648 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98648 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF V39_AEGIS_ONE_STEP_UP=LOW->MODERATE TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final Legacy and Aegis differ; FINAL: MODERATE, 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:H/I:N/A:H';CWE-125;CWE-129;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '6.3';DESCR 'An out-of-bounds read occurs in find_secret_in_page because the loop uses the total number of UV secrets instead of the number stored in the current page. When more than 85 secrets exist, a lookup for a secret located on a later page or not stored at all can make memcmp inspect entries beyond the current secrets array and may also return an out-of-bounds header after a false match. For the CVSS the PR:L reflects the conservative case where a local user or service account can reach the UV secret lookup interface without full administrative control. AC:H applies because exploitation requires a multi-page secret list and a lookup that crosses the current page boundary. The issue is not directly network reachable. Impact includes a possible kernel fault and potential exposure of adjacent memory through an out-of-bounds read. No write primitive is demonstrated, so privilege escalation is not established, but the memory disclosure and crash potential require manual review. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 6.3 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to MODERATE because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. 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 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 1 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE OOB SIMPLEFIX HARDWARE LINUS KPANIC_UNSUPPORTED_REMOVED V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Weak or indirect corruption candidate. `total_num_secrets` is an overall list count, but it is used as the bound for the per-page `secrets[]` array. With more than 85 secrets, `memcmp()` reads entries beyond that array. A coincidental match can also cause an out-of-bounds `hdr` value to be returned.
* +0 Reliable kernel crash. Reading beyond the array could theoretically fault, but neither the patch nor supplied context establishes a reliable kernel crash.
* +0 Confidentiality. No path copying the adjacent bytes to userspace, a guest, the network, or another observable output is shown. An internal `memcmp()` is not by itself a disclosure primitive.
* +0 Integrity. No write, active-state corruption, authorization bypass, or protected-state modification is present.
* +0 Local unprivileged reachability. The caller and permissions for the complete UV secret lookup operation are not supplied.
* No negative privilege penalty was applied because host-administrator privilege is not established.
* NEW52 B5-R does not apply because this is an OOB read, not a retry-accumulated heap OOB write.
* NEW53 B3-PENDING and the V32 through V34 rules do not apply because there is no shared-backing or checksum write.
* V33 does not apply because no attacker-influenced write to active structured state exists.
* NEW54 B4-PENDING does not apply because no DENY-to-ALLOW authorization decision is changed.
* Controlled disclosure, arbitrary write, UAF, privilege escalation, and remote reachability are not demonstrated.
3. Reachability analysis
The required state is a multi-page UV secret list containing more than 85 secrets, followed by a lookup for a secret in a later page or one that is absent. The supplied patch does not identify the userspace caller, device node, ioctl, sysfs interface, capability check, or ownership policy governing this lookup. Therefore, below-host-admin reachability and a local unprivileged trigger cannot be credited.
The s390 UV secret facility is global architecture-specific state rather than a namespace-scoped interface, so `NamespaceScopedPrivilege=NO`. Prior provisioning of more than 85 secrets is required, but the evidence does not establish whether the same actor performing the lookup can provision them. There is no race and no network trigger.
4. Primitive and severity interpretation
The exact primitive is a heap or page-backed array OOB read caused by using the global secret count as a per-page bound. It is not a UAF, repeated release, OOB write, shared-backing write, or active-state retirement defect.
The demonstrated operation reads an out-of-range secret ID through `memcmp()`. If those bytes equal the requested ID, it also consumes an out-of-range header and reports a false match. This is a limited invalid-read and invalid-result path, classified as `CLASS_C`.
The patch does not establish that adjacent bytes are disclosed or that the returned header controls a security-sensitive downstream operation. A kernel fault or useful false match remains possible but unresolved. Accordingly, this is not an Important candidate and may be automatically downgraded after recording the affected configuration. Manual review is still recommended to inspect callers, permissions, allocation layout, and handling of the returned header.
5. One-sentence report phrase
An incorrect per-page loop bound in s390 UV secret lookup can read beyond the current secrets array when more than 85 secrets exist, but no direct disclosure, write primitive, privilege escalation, or reliable crash is established.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Review the missing caller context to determine whether an unprivileged actor can perform lookups and whether a false out-of-bounds header can influence a security-sensitive consumer. The current evidence does not require Important preservation.
7. Call-site confidence
Call-site confidence: low
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: s390/uv: Prevent potential out-of-bounds read [ Upstream
Commit: 04bb5b2eb9f1d56110f14d3a4e31fa2c65fb026f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=04bb5b2eb9f1d56110f14d3a4e31fa2c65fb026f
Changed files:
arch/s390/kernel/uv.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=04bb5b2eb9f1d56110f14d3a4e31fa2c65fb026f
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98648 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98648
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:L/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:H
The Best / paranoid CVSS score: 6.3
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: 1
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 REGULAR
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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