[CVE-2026-99075][LOW] rust_binder: reschedule node refcount update on thread exit

[CVE-2026-99075][LOW] rust_binder: reschedule node refcount update on thread exit

[AL-KERNEL]

CVE: CVE-2026-99075
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: rust_binder: reschedule node refcount update on thread exit
Commit: 71cbad138969edecef01b28dff87d91b56db538d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=71cbad138969edecef01b28dff87d91b56db538d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99075
Analysis date: Mon, 26 Oct 2026 15:52:55 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A Binder thread exit can discard a pending node refcount notification and permanently retain the node, causing a local resource leak without demonstrated memory corruption or authorization bypass.

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

The original Linux kernel CVE announcement for CVE-2026-99075 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99075

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-2026-99075	LOW	https://www.kernelcve.org/list/?q=CVE-2026-99075 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=1 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:L/PR:L/UI:N/S:U/C:N/I:N/A:L';*CWE-772;CWE-404;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '3.3';DESCR 'The bug is a Binder node lifecycle and resource retention issue rather than demonstrated memory corruption. BINDER_THREAD_EXIT can cancel a pending node refcount increment and leave the delivery state inconsistent with the count state, preventing the node from being removed from the owning process node tree after external references are dropped. For the CVSS the PR:L value is used because a local process with Binder access must create the node activity and cause the relevant thread to exit. The base score uses AC:H because triggering depends on a pending deferred refcount update being assigned to the exiting thread. The demonstrated impact is limited availability loss through persistent per process node retention, with no supported UAF, OOB access, information leak, or write primitive. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 3.3 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_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore 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_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 1 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.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	DANGER INIT UAF LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
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; no stronger patch-supported primitive exists.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Local below-host-admin trigger: supplied evidence supports a local process with Binder access creating the relevant node activity and invoking `BINDER_THREAD_EXIT`.
* +1 Concrete persistent kernel resource/reference retention: cancellation drops delivery of a pending refcount increment, desynchronizing delivery/count state and potentially leaving the node permanently in the process node tree.
* No timing penalty: exit must occur with deferred work pending, but the evidence does not establish a narrow or externally uncontrollable race.
* No additional availability point: accumulation into material host-wide exhaustion is not demonstrated.
* No UAF, OOB access, repeated release, arbitrary write, controlled reclaim, disclosure, protected-state corruption, or authorization bypass is shown.
* NEW52/B5-R and NEW53/B3-PENDING do not apply: there is no OOB write or shared-backing write.

3. Reachability analysis

The supported actor is a below-host-admin local process with Binder access; host UID 0 is not required. Binder device access and applicable policy remain deployment prerequisites, but no host-admin operation, special hardware, namespace-scoped capability, or prior privileged per-object setup is shown. The actor can influence thread exit and node activity, although reliably arranging a pending deferred increment may require sequencing or timing. Namespace capability scope is not relevantly established.

4. Primitive and severity reading

The exact defect is cancellation-induced lifecycle bookkeeping desynchronization resulting in persistent node retention. It is passive invalid/resource state, not stale post-lifetime access or memory corruption, so `CLASS_C` is appropriate. The demonstrated effect is per-process resource leakage; broad exhaustion or host failure is unproven. There is no DENY-to-ALLOW authorization decision or protected-resource access. Consequently this is not an Important candidate and can be auto-downgraded.

5. One-sentence report phrase

A Binder thread exit can discard a pending node refcount notification and permanently retain the node, causing a local resource leak without demonstrated memory corruption or authorization bypass.

6. Manual review advice

NO MANUAL CHECK NEEDED

The patch establishes only constrained lifecycle/resource retention with no unresolved corruption or trust-boundary primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: rust_binder: reschedule node refcount update on thread exit
Commit: 71cbad138969edecef01b28dff87d91b56db538d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=71cbad138969edecef01b28dff87d91b56db538d

Commit description:

When a thread exits via BINDER_THREAD_EXIT, its pending work items are
cancelled. If a thread exits while holding a pending node refcount
increment (e.g. pushed as deferred work to that thread), the refcount
increment was previously dropped because Node::cancel() and
NodeWrapper::cancel() were no-ops.

Dropping the refcount update leaves the node's delivery state and count
state desynchronized, and userspace will not receive the notification,
which can cause the node to never be freed from the process's nodes tree
when all external references are dropped.

Fix this by implementing DeliverToRead::cancel() for Node and NodeWrapper
to move the pending refcount update to the process's work queue on thread
exit so another thread can deliver it to userspace.

Cc: stable <stable@kernel.org>
Fixes: eafedbc ("rust_binder: add Rust Binder driver")
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260903-binder-thread-exit-node-v1-1-be09ff14f6a4@google.com
[ Dropped first argument in calls to `push_work()` to adjust to the
  existing form without mainline commit dbb17c9 ("rust_binder: move
  (e)poll wait queue to Process"). - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/android/binder/node.rs
  drivers/android/binder/node/wrapper.rs

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=71cbad138969edecef01b28dff87d91b56db538d

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

The original Linux kernel CVE announcement for CVE-2026-99075 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99075

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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 3.3

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