* [CVE-2025-39694][LOW] s390/sclp: Fix SCCB present check
@ 2026-10-13 1:09 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-13 1:09 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2025-39694
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: s390/sclp: Fix SCCB present check
Commit: aa5073ac1a2a274812f3b04c278992e68ff67cc7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aa5073ac1a2a274812f3b04c278992e68ff67cc7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-39694
Analysis date: Mon, 12 Oct 2026 21:09:41 -0400
ActionableScore: 1
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-2025-39694 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-39694
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-2025-39694 LOW https://www.kernelcve.org/list/?q=CVE-2025-39694 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=LOW RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both LOW) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:N/A:H';**CWE-476;*CWE-20;CWE-682;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'The SCLP interrupt and tracing paths can treat a zero physical SCCB address as a valid pointer because __va(0) is not necessarily NULL when the s390 kernel identity mapping starts above address zero. The resulting pointer can reference the first page of the identity mapping, causing kernel code to read unrelated data as an SCCB header and potentially produce incorrect trace or response information. For the CVSS the PR:H value is used because reliable attacker controlled triggering would normally require privileged control over the s390 SCLP or virtualization environment rather than ordinary local user access. The issue is not network reachable and AC:H reflects the architecture specific mapping and interrupt conditions. The realistic impact is limited to incorrect reads and possible availability degradation. The paranoid score allows limited confidentiality impact if unrelated first page data reaches tracing and high availability impact if the invalid interpretation causes a fatal failure. No UAF, OOB write, arbitrary write, or credible privilege escalation primitive is visible in this code path.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE OOB SIMPLEFIX IMPROVEONLY LINUS LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 KPANIC_UNSUPPORTED_REMOVED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
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. A zero physical SCCB address is translated by `__va(0)` into a non-NULL pointer, and the first identity-mapped page can then be interpreted as an SCCB structure.
* +0 Reliable kernel crash. The commit establishes incorrect accesses but does not demonstrate an Oops, panic, or reliably fatal access.
* +0 Confidentiality. An internal read from an unintended page is established, but no user-visible or externally observable disclosure path is shown.
* +0 Integrity. No write, UAF, refcount mutation, or modification of protected state is established.
* +0 Remote or firmware-mediated attacker reachability. The path is entered from an SCLP interrupt, but attacker control over the interrupt parameter is not established.
* No privilege penalty was applied because host-admin-equivalent control is not positively established.
* No architecture rarity penalty was applied merely because the defect is s390-specific.
* NEW52 B5-R does not apply because there is no heap OOB write, retry accumulation, or later consumption of corrupted written state.
* NEW53 B3-PENDING does not apply because no shared-backing write exists.
* AuthorizationDecisionBypass is NO because this is a pointer-presence check, not an access-control DENY-to-ALLOW decision.
3. Reachability analysis
The vulnerable path is in the s390 SCLP interrupt handler. The supplied evidence does not establish that an ordinary user, namespace-scoped process, or remote peer can choose a zero SCCB interrupt address. It also does not prove that host-administrator action is required, so `HostAdminRequired=UNKNOWN` rather than YES.
No user-namespace or network-namespace capability participates in the path. SCLP or hypervisor mediation may be relevant in particular deployments, but attacker control through that boundary is not demonstrated. There is no race, retry loop, or repeatable userspace trigger in the supplied context.
4. Primitive and severity interpretation
The exact primitive is an invalid structured read: a zero physical address becomes a non-NULL virtual address and unrelated data in the first identity-mapped page may be consumed as an SCCB header. This is neither a real NULL dereference nor a lifetime violation.
There is no UAF, OOB write, arbitrary write, repeated release, authorization bypass, or established disclosure. The demonstrated behavior is therefore `CLASS_C`. A crash is technically possible if later parsing reaches an invalid address, but it is not demonstrated strongly enough for an additional DoS point.
`ImportantCandidate=NO` because no useful corruption, ownership, lifetime, or security-boundary primitive is established. `AutoDowngradeAllowed=YES` because the remaining issue is a constrained architecture-specific invalid-state read with no unresolved exploitation leverage.
5. One-sentence report phrase
A zero physical SCCB address can be translated into a non-NULL pointer and cause the s390 SCLP interrupt path to interpret the first identity-mapped page as SCCB data, but no write, disclosure path, UAF, or privilege-escalation primitive is established.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch establishes only a constrained invalid-read condition without attacker reachability, memory writes, lifetime corruption, or an authorization boundary bypass.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: s390/sclp: Fix SCCB present check
Commit: aa5073ac1a2a274812f3b04c278992e68ff67cc7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aa5073ac1a2a274812f3b04c278992e68ff67cc7
Commit description:
Tracing code called by the SCLP interrupt handler contains early exits
if the SCCB address associated with an interrupt is NULL. This check is
performed after physical to virtual address translation.
If the kernel identity mapping does not start at address zero, the
resulting virtual address is never zero, so that the NULL checks won't
work. Subsequently this may result in incorrect accesses to the first
page of the identity mapping.
Fix this by introducing a function that handles the NULL case before
address translation.
Fixes: ada1da3 ("s390/sclp: sort out physical vs virtual pointers usage")
Cc: [email protected]
Reviewed-by: Alexander Gordeev <[email protected]>
Signed-off-by: Peter Oberparleiter <[email protected]>
Signed-off-by: Alexander Gordeev <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/s390/char/sclp.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=aa5073ac1a2a274812f3b04c278992e68ff67cc7
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2025-39694 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-39694
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:H/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:N/A:H
The Best / paranoid CVSS score: 4.7
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: 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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