* [CVE-2026-99169][LOW] futex: Fix mm reuse handling for FUT_OFF_MMSHARED [ Upstream
@ 2026-10-29 3:02 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-29 3:02 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99169
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: futex: Fix mm reuse handling for FUT_OFF_MMSHARED [ Upstream
Commit: c17cc2027773e8e4913c5ab0fe3a489b1ed5bf81
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c17cc2027773e8e4913c5ab0fe3a489b1ed5bf81
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99169
Analysis date: Wed, 28 Oct 2026 23:02:45 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
MM address reuse can make a stale shared-futex waiter consume a wakeup intended for a new MM, potentially leaving a local process blocked without demonstrated kernel memory corruption.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99169 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99169
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-2026-99169 LOW https://www.kernelcve.org/list/?q=CVE-2026-99169 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=2 LEGACY=LOW RESULT=DIFF (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE) 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-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A stale FUT_OFF_MMSHARED waiter can retain an MM address as its futex identity after that MM is freed. If a new mm_struct is allocated at the same address, the stale waiter can falsely match the new MM and consume a wakeup intended for its futex, causing a thread or process to remain blocked. This is an MM address reuse or ABA style logic issue and not a demonstrated UAF dereference because the stale pointer value is compared as a key rather than dereferenced. For the CVSS the PR:L value reflects that local code execution and access to futex operations are required. AC:H reflects the need to arrange cross-MM requeue behavior, MM destruction, allocator address reuse, and matching wake timing. The demonstrated impact is availability loss through missed wakeups. No concrete information leak, kernel memory write, or privilege escalation primitive is established. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to LOW because the CVSS score, vector or bug class threshold rule was applied. final reconciliation stage LOW to LOW 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 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH and KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. 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 OOB INIT LEAK UAF LINUS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 2.
* Paranoid score: 2; stronger effects require unsupported memory-corruption or privilege-bypass assumptions.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Local unprivileged trigger: ordinary processes can use futex wait/requeue operations without host-administrator privilege.
* +1 Weak/indirect invalid-state effect: an MM address reused as a futex key can falsely select stale waiters and direct a wakeup to the wrong waiter.
* +1 Availability impact: consuming the intended wakeup can leave a thread or process blocked.
* -1 Hard/special timing: exploitation requires cross-MM requeueing, destruction of the original MM, reuse of the same `mm_struct` address, and appropriately timed wake activity.
* No crash point: the patch establishes a lost-wakeup/process-blocking condition, not a kernel panic.
* No Real UAF: the stale MM address is compared as an identity key and is not dereferenced.
* No kernel write, controlled reclaim, disclosure, authorization bypass, or privilege escalation is shown.
* NEW52/B5-R does not apply: there is no heap OOB write or retry-accumulated offset.
* NEW53/B3-PENDING does not apply: no shared-backing data write exists.
* B4-PENDING does not apply: no security guard changes from DENY to ALLOW.
3. Reachability analysis
A normal local process can invoke the relevant futex operations; no UID 0, capability, namespace privilege, prior privileged setup, special hardware, or unusual configuration is shown as necessary. The required MM-address reuse and wake ordering materially raise trigger complexity, although repeated process creation may provide multiple attempts.
4. Primitive and severity reading
The primitive is an ABA-style futex-key identity collision: a stale `FUT_OFF_MMSHARED` waiter remains keyed by an old MM pointer value, and a newly allocated MM at the same address can falsely match it. This is scalar stale identity state, not active-object dereference or fixed stale storage access. The demonstrated effect is wakeup misdelivery and user-process availability loss. Kernel memory corruption, host-wide DoS, confidentiality/integrity impact, and useful exploitation leverage past blocking are unproven. It is therefore CLASS_C, not an Important candidate, and ordinary Moderate downgrade remains permissible.
5. One-sentence report phrase
MM address reuse can make a stale shared-futex waiter consume a wakeup intended for a new MM, potentially leaving a local process blocked without demonstrated kernel memory corruption.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm practical reproducibility and whether affected workloads can turn the lost wakeup into broader service-level denial of service.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: futex: Fix mm reuse handling for FUT_OFF_MMSHARED [ Upstream
Commit: c17cc2027773e8e4913c5ab0fe3a489b1ed5bf81
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c17cc2027773e8e4913c5ab0fe3a489b1ed5bf81
Changed files:
include/linux/futex.h
include/linux/mm_types.h
kernel/futex/core.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=c17cc2027773e8e4913c5ab0fe3a489b1ed5bf81
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99169 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99169
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:L
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: 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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