* [CVE-2026-98777][MODERATE REGULAR] binder: fix leaked fd fixups on TF_UPDATE_TXN supersede
@ 2026-10-24 10:38 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 10:38 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98777
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: binder: fix leaked fd fixups on TF_UPDATE_TXN supersede
Commit: 7fd609fb0e9dcbc4d7a1e4da1af5368c0555ff55
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7fd609fb0e9dcbc4d7a1e4da1af5368c0555ff55
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98777
Analysis date: Sat, 24 Oct 2026 06:38:16 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
A local Binder client can repeatedly leak file references through `TF_UPDATE_TXN` supersession, potentially exhausting system file resources.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98777 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98777
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98777 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98777 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: 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-772;*CWE-401;CWE-775;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 Binder cleanup omission causes an outdated asynchronous transaction replaced through TF_UPDATE_TXN to be freed lacking cleanup of its fd fixups. Each leaked fixup retains an fget acquired struct file reference, so affected file objects remain pinned after process exit and repeated triggering can accumulate persistent resource usage. For the CVSS the PR:L value is used because exploitation requires a local process able to use Binder and submit suitable asynchronous transactions with file descriptors. AC:H reflects the additional requirement that a pending transaction for a frozen process must be superseded through the TF_UPDATE_TXN path. The demonstrated primitive is a persistent file reference leak rather than UAF, OOB access, or another memory corruption primitive. Confidentiality and integrity remain unaffected. Availability impact is low for an isolated trigger, while sustained repeatable abuse may eventually exhaust file resources and cause system wide denial of service. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage LOW to MODERATE because the ActionableScore threshold 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 INCREASED_FROM_LOW_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN3 and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4. The independent weaker Aegis shadow evaluated CVSS 4.3 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';NO MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) MAYBE INIT LEAK ERRORPATH UAF LINUS INCREASED_FROM_LOW_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN3 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
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: 3.
* Conservative score: 3; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; no separate defensible paranoid bonus.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +1 Concrete persistent kernel resource/reference leak: `t_outdated` is freed without `binder_free_txn_fixups()`, permanently retaining each fixup’s `fget()` reference.
* +1 Local below-host-admin trigger: supplied evidence supports a local Binder client submitting suitable asynchronous transactions and file descriptors; host administrator or UID 0 is not required.
* +1 Strong DoS: the commit specifically states that leaked file references survive process exit and can accumulate across invocations until file-table exhaustion.
* No timing penalty: frozen-target and `TF_UPDATE_TXN` supersession are additional state requirements, but no narrow or uncontrollable race is shown.
* No extra availability point: file exhaustion is the same DoS already counted.
* No UAF, OOB access, memory overwrite, authorization bypass, confidentiality impact, integrity impact, or protected-resource access is shown.
* NEW52/B5-R and NEW53/B3-PENDING do not apply: there is neither an OOB write nor a shared-backing write.
3. Reachability analysis
A below-host-admin local Binder client can provide transactions containing file descriptors. Triggering additionally requires a pending asynchronous transaction for a frozen process to be superseded through `TF_UPDATE_TXN`, followed by repetition for meaningful exhaustion. No namespace capability, host UID 0, special hardware, boot option, or separate privileged setup is evidenced. The exact practicality and rate of sustained exhaustion are not established.
4. Primitive and severity reading
The exact primitive is a persistent `struct file` reference leak caused by omitted fixup cleanup before transaction destruction. It is not stale-object use: the references remain valid but permanently pinned. The shown consequence is cumulative resource exhaustion; memory corruption and non-availability security effects are unsupported. This is CLASS_C DoS/resource-management behavior, not an Important-preserving primitive. Auto-downgrade remains allowed.
5. One-sentence report phrase
A local Binder client can repeatedly leak file references through `TF_UPDATE_TXN` supersession, potentially exhausting system file resources.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm practical repeatability and whether product-level Binder limits materially contain file-table exhaustion.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: binder: fix leaked fd fixups on TF_UPDATE_TXN supersede
Commit: 7fd609fb0e9dcbc4d7a1e4da1af5368c0555ff55
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7fd609fb0e9dcbc4d7a1e4da1af5368c0555ff55
Commit description:
When a TF_UPDATE_TXN transaction supersedes a pending async transaction
in a frozen process, the outdated transaction is freed with kfree()
directly. This skips binder_free_txn_fixups(), leaking all
binder_txn_fd_fixup entries and their fget()'d struct file references.
The leaked file refcounts never reach zero, so the struct file objects
are permanently pinned in memory. They survive process exit and
accumulate across invocations until file-max exhaustion.
Every other transaction cleanup path (binder_free_transaction(),
binder_transaction() error paths, binder_release_work()) correctly
calls binder_free_txn_fixups(). Add the missing call before kfree()
in the t_outdated cleanup block.
Fixes: 9864bb4 ("Binder: add TF_UPDATE_TXN to replace outdated txn")
Cc: stable <[email protected]>
Signed-off-by: Tomer Pomeranc <[email protected]>
Acked-by: Carlos Llamas <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/android/binder.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=7fd609fb0e9dcbc4d7a1e4da1af5368c0555ff55
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98777 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98777
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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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