* [CVE-2026-99103][MODERATE 7.0] Revert "workqueue: Implement system-wide nr_active enforcement for unbound workqueues" This reverts commit 5a70bae which is
@ 2026-10-30 15:44 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-30 15:44 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99103
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Revert "workqueue: Implement system-wide nr_active enforcement for unbound workqueues" This reverts commit 5a70bae which is
Commit: 6741dd3fd38e47c08bc39d11ef5fa141fa6d0441
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6741dd3fd38e47c08bc39d11ef5fa141fa6d0441
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99103
Analysis date: Fri, 30 Oct 2026 11:44:43 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A privileged workqueue reconfiguration sequence can prematurely free an unbound worker pool while a pending PWQ still references it, causing a stale pool-lock access and potential kernel crash.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99103 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99103
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-99103 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99103 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'An unbound pool lifetime race leaves an empty pwq reachable from pending_pwqs after its reference count reaches zero. pwq_release_workfn can drop the final worker_pool reference before unlinking that pwq, allowing RCU to free the pool while node_activate_pending_pwq or work completion still dereferences it and accesses the freed pool lock. The demonstrated primitive is a slab use after free in raw_spin_trylock and can cause a kernel crash or corrupt workqueue synchronization state. For the CVSS the PR:H value reflects that the demonstrated setup changes workqueue attributes through a privileged control path and no reliable unprivileged trigger is established. AC:H reflects the required cancellation, final reference release, RCU reclamation, and later pending pwq activation sequence. The paranoid impact considers possible memory corruption if the freed slab is reused before the stale spinlock operation, but controlled reuse and privilege escalation are not proven. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 6.4 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 MODERATE to MODERATE_KPANIC because 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 V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 5.1 and ActionableScore 5 with primitive class CLASS_B and manual review REQUIRED. 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_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE READ LOCK DEADLOCK INIT LEAK UAF HARDWARE LINUS KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor applied: the demonstrated attacker-invocable setup uses a host-privileged workqueue-attribute control path.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +2 — Real active-object UAF: `put_unbound_pool()` can drop the final pool reference while the PWQ remains linked on `pending_pwqs`; RCU can free the pool before `node_activate_pending_pwq()` accesses `pool->lock`.
* +1 — Plausible kernel crash/strong DoS: KASAN confirms a stale slab access in `_raw_spin_trylock()`.
* -2 — Demonstrated trigger setup is host-admin-equivalent through the global workqueue attribute path.
* No race penalty: the sequence is complex, but the evidence does not establish a narrow, uncontrollable, one-shot timing window.
* No controlled reclaim, attacker-shaped replacement, arbitrary write, disclosure, or privilege escalation is shown. The possible spinlock RMW into reused storage is not sufficiently established as a separately useful corrupt primitive.
* No extra availability point: it would duplicate the same UAF-induced crash.
* No repeated release/refcount signal: the defect is premature release followed by stale lock access, not a second lifetime mutation through the same dangling reference.
* NEW52/B5-R and B3/B4 pending profiles do not apply.
3. Reachability analysis
The evidenced setup reaches `wq_nice_store()` through a host-global privileged workqueue control interface. No normal-user, delegated capability, user-namespace, guest, or container-scoped complete trigger is shown. Numeric host UID 0 specifically is not established, so `RequiresHostUID0` remains unknown. The cancellation/release/RCU/activation ordering occurred in practice, but attacker repeatability and timing control are unresolved.
4. Primitive and severity reading
This is a CLASS_B UAF of an active structured `worker_pool`. The release occurs in cleanup work, but the stale object is subsequently consumed by active pending-PWQ processing through its lock. The shown result is a KASAN-detected stale lock access with plausible host crash. Useful post-reuse corruption remains theoretical; there is no specific trust-boundary crossing or attacker-controlled replacement. Accordingly, it is not an Important candidate and may be downgraded after review.
5. One-sentence report phrase
A privileged workqueue reconfiguration sequence can prematurely free an unbound worker pool while a pending PWQ still references it, causing a stale pool-lock access and potential kernel crash.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm whether any non-host-admin kernel interface can induce the complete PWQ cancellation and pool-release sequence.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: Revert "workqueue: Implement system-wide nr_active enforcement for unbound workqueues" This reverts commit 5a70bae which is
Commit: 6741dd3fd38e47c08bc39d11ef5fa141fa6d0441
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6741dd3fd38e47c08bc39d11ef5fa141fa6d0441
Commit description:
The workqueue patches backported to 6.6.y caused some reported
regressions, so revert them for now.
Reported-by: Thorsten Leemhuis <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Sasha Levin <[email protected]>
Cc: Audra Mitchell <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
include/linux/workqueue.h
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=6741dd3fd38e47c08bc39d11ef5fa141fa6d0441
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99103 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99103
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:H/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 6.4
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: YES
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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2026-10-30 15:44 21% [CVE-2026-99103][MODERATE 7.0] Revert "workqueue: Implement system-wide nr_active enforcement for unbound workqueues" This reverts commit 5a70bae which is AL-KERNEL
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