* [CVE-2026-93268][LOW] ext4: skip extra isize expansion during mount to prevent deadlock [ Upstream
@ 2026-09-25 0:40 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-25 0:40 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-93268
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ext4: skip extra isize expansion during mount to prevent deadlock [ Upstream
Commit: 41897f1bcf4ace5f1f28d0be784b6f4f0e929641
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=41897f1bcf4ace5f1f28d0be784b6f4f0e929641
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93268
Analysis date: Thu, 24 Sep 2026 20:40:33 -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-2026-93268 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93268
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-2026-93268 LOW https://www.kernelcve.org/list/?q=CVE-2026-93268 CHECK WITH IMPACT FROM ORIG NN 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-833;CWE-667;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'An ext4 mount path can deadlock because extra isize expansion may release an xattr inode while an active jbd2 handle is held. During mount before SB_ACTIVE is set, the resulting iput path can acquire s_writepages_rwsem and form a circular lock dependency with the journal and xattr locks. This can stall filesystem mounting or inode processing and cause a local denial of service. For the CVSS the paranoid score uses PR:L because some deployments delegate mounting of controlled storage images or volumes to reduced privilege service accounts. The issue is not network reachable by itself. No confidentiality integrity or privilege escalation impact is supported because the patch describes a lock dependency and not a memory corruption primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES DEADLOCK DANGER DISK RACE LINUS SYZBOT DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Reliable denial of service. The circular lock dependency can stall the ext4 mount or inode-processing path.
* +1 Important filesystem path. The issue occurs in ext4 mount-time processing involving journaling, xattrs, orphan handling, and inode eviction.
* +0 No memory-corruption primitive. The patch establishes a lock-order deadlock, not a UAF, double free, OOB access, stale reference, or invalid refcount mutation.
* +0 No confidentiality or integrity impact. No disclosure, unauthorized modification, ownership violation, or security-boundary bypass is demonstrated.
* +0 No local-unprivileged-trigger bonus. The supplied evidence does not establish that an ordinary user can perform the complete mount and trigger sequence.
* +0 No host-admin penalty. The supplied evidence does not positively establish host-admin-equivalent privilege as a complete prerequisite.
* +0 No race penalty. This is a deterministic lock-order cycle in a particular mount-time path, not an externally narrow timing race.
* +0 No paranoid increase. There is no technically supported stronger primitive beyond mount-path deadlock and local availability impact.
3. Reachability analysis
The vulnerable path is reached while mounting an ext4 filesystem before SB_ACTIVE is set. A suitable filesystem state must cause orphan processing or inode eviction to invoke ext4_mark_inode_dirty and then ext4_try_to_expand_extra_isize.
The supplied patch does not establish whether mounting the relevant filesystem image requires host administrator privilege, delegated mount rights, or a service-controlled storage workflow. Therefore HostAdminRequired is UNKNOWN.
NamespaceScopedPrivilege is also UNKNOWN. No evidence establishes that the complete ext4 mount and affected journaling path can be reached using only attacker-obtainable namespace-scoped capabilities. No network, firmware, special hardware, boot option, or sysctl prerequisite is indicated.
4. Primitive and severity interpretation
The exact primitive is a circular locking dependency:
s_writepages_rwsem -> jbd2_handle -> xattr_sem -> s_writepages_rwsem.
During mount, extra isize expansion can move xattrs and call iput on an EA inode. Before SB_ACTIVE is set, iput may invoke write_inode_now and acquire s_writepages_rwsem while the caller already holds an active jbd2 handle.
This is a logic and synchronization defect producing deadlock or stalled filesystem processing. It is not an active structured-object UAF, fixed stale storage issue, refcount misuse, repeated release, or memory corruption primitive.
The demonstrated consequence is local denial of service through a hung mount or blocked ext4 inode-processing path. Privilege escalation, arbitrary write, confidentiality impact, integrity impact, and persistent filesystem metadata corruption are speculative and not supported by the patch. ImportantCandidate is NO and AutoDowngradeAllowed is YES because no unresolved corruption, ownership, authorization, or lifetime primitive remains.
Likely operational severity is low to ordinary Moderate. Systems that mount untrusted removable media or service-provided ext4 images may prioritize the fix operationally, but the supplied evidence does not support Important-class security severity.
5. One-sentence report phrase
An ext4 mount-time lock-order deadlock can stall filesystem mounting or inode processing when extra isize expansion releases an xattr inode before SB_ACTIVE is set.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch demonstrates a deadlock-only availability issue without a concrete memory-corruption, authorization-bypass, ownership, disclosure, or privilege-escalation primitive.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ext4: skip extra isize expansion during mount to prevent deadlock [ Upstream
Commit: 41897f1bcf4ace5f1f28d0be784b6f4f0e929641
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=41897f1bcf4ace5f1f28d0be784b6f4f0e929641
Changed files:
fs/ext4/inode.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=41897f1bcf4ace5f1f28d0be784b6f4f0e929641
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93268 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93268
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:H/UI:N/S:U/C:N/I:N/A:H
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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