[CVE-2026-98281][MODERATE REGULAR] futex: Also allocate private hash on vfork() [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-98281
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: futex: Also allocate private hash on vfork() [ Upstream
Commit: 5468a4855b63b30156a79e5248e01bf1a2c18dd7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5468a4855b63b30156a79e5248e01bf1a2c18dd7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98281
Analysis date: Sat, 10 Oct 2026 17:57:49 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98281 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98281

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-98281	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98281 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (independent 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:N/I:N/A:H';CWE-362;CWE-667;*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 race and initialization ordering flaw can allow a private futex waiter to exist before the shared mm receives its private futex hash when vfork is used. This may make waiter insertion and later wake or removal operations select inconsistent hash state, potentially leaving tasks blocked and causing a local denial of service. For the CVSS the PR:L is selected because an unprivileged local process context is required to invoke vfork and futex operations. AC:H is selected because reliable triggering appears to depend on reaching a timing window while the shared mm is accessible and before hash allocation completes. The issue is not network reachable. The available change does not establish a UAF, an out of bounds access, an information leak, or an arbitrary write primitive, so the supported impact is availability rather than confidentiality or integrity. The paranoid assessment allows A:H if repeated triggering can reliably stall multiple tasks or a critical local service.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	SIMPLEFIX LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=3
ActionableScoreLower=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 conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative signals:

* +1 Local unprivileged trigger. Ordinary processes can invoke `vfork()` and futex operations without host-administrator privileges.
* +1 Broadly deployed exposure. Futexes, shared address spaces, and `vfork()` are standard kernel functionality, and the affected logic allocates the default private futex hash.
* Total: 2.

Additional paranoid signal:

* +1 Availability impact. A private waiter inserted before private-hash allocation may become inconsistent with later hash selection, plausibly causing a missed wake or indefinitely blocked task.
* Total: 3.

Not awarded:

* No UAF, OOB access, arbitrary write, refcount corruption, or repeated release is established.
* No reliable kernel crash or host-wide DoS is demonstrated.
* No extra availability point was awarded for repeatability.
* No race penalty was applied because the timing is not shown to be narrow or difficult to repeat.
* No confidentiality, integrity, authorization-bypass, B3-PENDING, B4-PENDING, or B5-R signal applies.
* Controlled reclaim and privilege escalation are not demonstrated.

Repeated-release checks:

* First lifetime-ending release: not present.
* Same reference surviving a release: not present.
* Second lifetime/refcount mutation: not present.
* Concrete repeated release/refcount +1: not awarded.
* Paranoid repeated-refcount +1: not awarded.
* FLOOR 5: not applicable.

3. Reachability analysis

An ordinary local process can invoke `vfork()`, whose child shares the parent MM through `CLONE_VM`. The commit establishes that the shared MM can be accessed during this interval and that private futex waiters can appear before private-hash allocation.

No capability, host UID 0, namespace privilege, prior privileged setup, special device, boot option, or hardware prerequisite is identified. The operation is therefore below host-admin privilege and is not dependent on namespace-scoped authority. Network reachability is absent.

The attacker can invoke the relevant process and futex operations, but the supplied patch does not show how reliably the ordering can be forced or how broadly the resulting waiter inconsistency affects other tasks. No hard-race penalty is justified.

4. Primitive and severity interpretation

The established primitive is an initialization-ordering violation in active futex hash state. A private waiter may exist before the shared MM receives the private hash that later operations expect to use.

This is not a demonstrated post-lifetime access, so `RealUAF=NO`. It is also not a concrete heap overwrite, stale-object reuse, repeated refcount mutation, or authorization bypass. The best-supported classification is `CLASS_C`: inconsistent active state with a plausible missed-wake or task-hang consequence.

The patch-supported practical consequence is limited availability loss affecting futex waiters. A broader service stall is technically defensible for paranoid triage, but host-wide failure, memory corruption, confidentiality impact, integrity impact, and privilege escalation remain unsupported.

`ImportantCandidate=NO` because no Important-preserving corruption, ownership, lifetime, or security-boundary primitive is established. `AutoDowngradeAllowed=YES` because the unresolved behavior remains an ordering and availability issue without meaningful exploitation leverage beyond a possible hang.

5. One-sentence report phrase

A local unprivileged process may use vfork related shared MM access to create private futex waiters before private hash initialization, potentially causing inconsistent waiter lookup and task hangs.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review the private-hash allocation and waiter lookup call sites to determine whether preexisting waiters can only be stranded or whether hash replacement can expose a stronger stale-bucket or memory-lifetime condition.

7. Call-site confidence

Call-site confidence: medium

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: futex: Also allocate private hash on vfork() [ Upstream
Commit: 5468a4855b63b30156a79e5248e01bf1a2c18dd7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5468a4855b63b30156a79e5248e01bf1a2c18dd7

Changed files:
  kernel/fork.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=5468a4855b63b30156a79e5248e01bf1a2c18dd7

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98281 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98281

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: 2
  Paranoid ActionableScore: 3

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).