* [CVE-2026-98888][LOW] arm64: kprobes: Allow reentering kprobes while single-stepping [ Upstream
@ 2026-10-26 19:59 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-26 19:59 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98888
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: arm64: kprobes: Allow reentering kprobes while single-stepping [ Upstream
Commit: bb0fe9121aa0824211aafa33c7d0151fd25ddb75
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bb0fe9121aa0824211aafa33c7d0151fd25ddb75
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98888
Analysis date: Mon, 26 Oct 2026 15:59:08 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
An arm64 kprobe single-step reentry can mishandle nested state and leave interrupts masked, causing a timing-dependent local kernel or CPU denial of service.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98888 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98888
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-2026-98888 LOW https://www.kernelcve.org/list/?q=CVE-2026-98888 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both LOW) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-755;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'An arm64 kprobe hit during KPROBE_HIT_SS was incorrectly treated as an unrecoverable nested reentry even though the one level prev_kprobe save area was still available. Tracing or perf execution from the debug exception path can produce this condition and reach fatal kprobe handling, causing a local kernel crash or CPU disruption. For the CVSS the PR:H base value reflects that configuring and controlling kernel probes normally requires administrative tracing privileges. The paranoid PR:L value covers a system with preconfigured probes where a local user can repeatedly invoke the probed kernel path, while AC:H reflects the need to hit the narrow single step reentry window. No UAF, OOB access, information leak, or write primitive is shown, so confidentiality and integrity remain unaffected. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. 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. The independent weaker Aegis shadow evaluated CVSS 2.0 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE DMAorINTERRUPT HARDWARE LINUS - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
ActionableScoreLower=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 0 (+1 kernel/CPU DoS, -1 narrow single-step reentry timing).
* Conservative score: 0; no floor or cap applies.
* Raw paranoid score: 1 (+1 DoS, +1 local invocation of a preconfigured probed path, -1 timing).
* Paranoid score: 1; no floor or cap applies.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Reliable kernel crash / strong DoS: unrecoverable reentry handling can disrupt the kernel, while loss of the outer saved DAIF state can leave interrupts permanently masked.
* -1 Hard timing: the trigger requires another probe hit while the outer probe is specifically in `KPROBE_HIT_SS`, through tracing or perf execution in the debug-exception path.
* Paranoid +1 Local trigger: supplied evidence supports a local user repeatedly invoking a kernel path containing probes that were already configured by a privileged actor.
* No UAF, OOB access, repeated release, memory overwrite, disclosure, authorization bypass, or integrity primitive is shown.
* No extra Availability point: permanent interrupt masking and resulting crash/disruption are the same DoS consequence.
* NEW52/B5-R does not apply: there is no heap OOB write, retry-accumulated index, or later consumption of corrupted heap state.
* NEW53/B3-PENDING does not apply: no shared-backing write exists.
3. Reachability analysis
Installing or controlling kprobes normally requires privileged tracing configuration. A lower-privileged process may trigger a preconfigured probed path, but the supplied source does not establish the precise tracefs/perf permissions or a complete namespace-scoped setup. Therefore effective host-admin requirements and namespace capability scope remain unknown. Prior privileged probe setup is required for the lower-privilege scenario. No special hardware is required.
4. Primitive and severity reading
The defect is incorrect nested-probe state handling: `KPROBE_HIT_SS` is treated as unrecoverable, and nested entry overwrites the outer probe’s saved interrupt flags. The patch adds one-level state preservation and restores the original DAIF value. This is CLASS_C invalid-state/DoS behavior, not active-object corruption or a security-boundary primitive. The shown impact is crash or CPU disruption; memory corruption, LPE, and confidentiality/integrity effects are unsupported. ImportantCandidate is therefore NO, and auto-downgrade is allowed.
5. One-sentence report phrase
An arm64 kprobe single-step reentry can mishandle nested state and leave interrupts masked, causing a timing-dependent local kernel or CPU denial of service.
6. Manual review advice
NO MANUAL CHECK NEEDED
The patch shows a constrained reentry-state DoS without a memory-corruption, lifetime, authorization, or cross-boundary primitive.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: arm64: kprobes: Allow reentering kprobes while single-stepping [ Upstream
Commit: bb0fe9121aa0824211aafa33c7d0151fd25ddb75
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bb0fe9121aa0824211aafa33c7d0151fd25ddb75
Changed files:
arch/arm64/include/asm/kprobes.h
arch/arm64/kernel/probes/kprobes.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=bb0fe9121aa0824211aafa33c7d0151fd25ddb75
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98888 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98888
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:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/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: 0
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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