[CVE-2026-98388][LOW] exec: do_close_on_exec() before taking exec_update_lock

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

CVE: CVE-2026-98388
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: exec: do_close_on_exec() before taking exec_update_lock
Commit: 955973fff4a36d39a848b00cac1706863f568fe1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=955973fff4a36d39a848b00cac1706863f568fe1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98388
Analysis date: Wed, 14 Oct 2026 22:35:04 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98388 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98388

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-2026-98388	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98388 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT LOW AEGIS_AS=2 LEGACY=LOW RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both 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-833;CWE-667;**CWE-400;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 blocking do_close_on_exec operation could run while exec_update_lock was held and wait for a filesystem flush reply. A FUSE daemon that inspects the process responsible for the request could enter a path that also needs exec_update_lock and create a deadlock. A hung filesystem could also keep the lock held and block other access checks or process state operations involving the affected task. For the CVSS the PR:L value is selected because a local user or process must prepare a CLOEXEC file descriptor on a suitable filesystem and invoke exec. The issue is not directly network reachable. The demonstrated impact is local denial of service through a hung exec or blocked process operations. No UAF OOB access or other memory corruption primitive is visible in the changed execution path. 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. 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. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 2 with primitive class CLASS_C and manual review NO. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	READ DEADLOCK DISK INIT SIMPLEFIX RACE LINUS  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +1 Local unprivileged trigger. An ordinary process can create a CLOEXEC descriptor, invoke exec, and interact with an accessible FUSE filesystem without host-administrator powers in the established attacker model.
* +1 Strong local DoS. A blocking filesystem flush while holding exec_update_lock can form a deterministic lock cycle with a FUSE daemon inspecting the caller, leaving exec and related process-state operations blocked.

Negative signals:

* No negative points. Host-admin privilege, unusual hardware, a hard race, and a rare execution mode are not established.

Important non-awarded signals:

* No UAF, OOB access, heap overwrite, repeated release, refcount mutation, or other memory-corruption primitive is established.
* No authorization DENY-to-ALLOW transition is fixed. exec_update_lock protects access-check synchronization, but moving a blocking call outside that lock does not bypass or restore an authorization decision.
* No confidentiality, integrity, privilege-escalation, protected-resource, or cross-boundary consequence is established.
* No remote-reachability point is awarded.
* No extra Availability point is awarded because the blocked exec and related lock wait are the same DoS mechanism.
* NEW52 B5-R does not apply because no retry-accumulated OOB write exists.
* NEW53 B3-PENDING does not apply because no shared-backing write exists.
* NEW54 B4-PENDING does not apply because no concrete authorization bypass exists.

3. Reachability analysis

The evaluated attacker is an ordinary local process using a CLOEXEC descriptor associated with a FUSE filesystem and then invoking exec. A FUSE daemon that inspects the requesting process can request state protected by exec_update_lock and deadlock against the exec path that is waiting for the daemon response.

No capability namespace is part of the vulnerable operation, so NamespaceScopedPrivilege is NO. Host UID 0 is not required. Common unprivileged FUSE deployment may depend on prior system exposure of the FUSE interface, but the complete operation does not inherently require host-admin-equivalent authority.

This is not a timing race requiring a narrow probabilistic window. It is a lock-order and blocking-operation problem that can arise from an ordered request and response cycle. No special hardware, boot mode, or network trigger is required.

4. Primitive and severity interpretation

The exact primitive is a deadlock caused by executing potentially blocking filesystem flush handlers while holding exec_update_lock. The vulnerable path can wait for a FUSE daemon while that daemon enters a process-inspection path requiring the same lock.

This is CLASS_C because the demonstrated behavior is blocking and denial of service without memory corruption, stale post-lifetime access, ownership violation, or authorization bypass. It is neither active structured UAF nor fixed stale storage. No repeated release or refcount operation exists.

The demonstrated consequence is a hung exec and blocked process-state operations involving the affected task. Wider service disruption is possible when an affected FUSE daemon or service participates, but host crash, global system deadlock, and privilege escalation are not established.

ImportantCandidate is NO because there is no Important-preserving primitive. AutoDowngradeAllowed is YES because the issue is a bounded locking DoS with no unresolved corruption or security-boundary mechanism.

5. One-sentence report phrase

Holding exec_update_lock across do_close_on_exec could deadlock exec against a FUSE daemon or hung filesystem and block related process-state operations, resulting in local denial of service without a demonstrated memory-corruption or authorization-bypass primitive.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a locking regression and local DoS, but no UAF, overwrite, authorization bypass, protected-resource access, or other unresolved Important-grade primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: exec: do_close_on_exec() before taking exec_update_lock
Commit: 955973fff4a36d39a848b00cac1706863f568fe1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=955973fff4a36d39a848b00cac1706863f568fe1

Commit description:

do_close_on_exec() currently happens while holding the exec_update_lock,
which is used in a lot of places that access process state to
synchronize access checks.
I recently added another such use of exec_update_lock, causing a
regression.

do_close_on_exec() can block waiting for a reply from a filesystem.
That means a hung filesystem can block codepaths that use
exec_update_lock; and it also means that a FUSE filesystem which
attempts to inspect the calling process can deadlock.

To avoid such problems, move do_close_on_exec() before the
exec_update_lock is taken, but after the FD table has been copied if
necessary.

I have looked through all the calls between the old and new position of
the do_close_on_exec() call; there seems to be no file descriptor table
access in between.

Reported-by: Benjamin Peterson <benjamin@locrian.net>
Closes: https://lore.kernel.org/r/f5e8166a-88be-46c5-8939-1e5227ffe4c2@app.fastmail.com
Fixes: 6650527 ("proc: protect ptrace_may_access() with exec_update_lock (part 1)")
Cc: stable@vger.kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Link: https://patch.msgid.link/20260907-cloexec-before-exec-update-lock-v1-1-8018c201a7df@google.com
Tested-by: Benjamin Peterson <benjamin@locrian.net>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/exec.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=955973fff4a36d39a848b00cac1706863f568fe1

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

The original Linux kernel CVE announcement for CVE-2026-98388 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98388

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