[CVE-2026-74358][MODERATE REGULAR] ext4: fix fast commit wait/wake bit mapping on 64-bit [ Upstream

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

CVE: CVE-2026-74358
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ext4: fix fast commit wait/wake bit mapping on 64-bit [ Upstream
Commit: e82d515092a0cf2bca92f399d5c330c324879cea
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e82d515092a0cf2bca92f399d5c330c324879cea
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74358
Analysis date: Sat, 15 Aug 2026 07:02:51 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended
Manual review required: YES

Summary:
An ext4 fast commit wait and wake bit mapping bug on 64 bit systems can cause tasks to wait on the wrong inode state key, potentially stalling filesystem operations and causing a local denial of service.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74358 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74358

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
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CVE-2026-74358	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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:H';CWE-667;CWE-662;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'ext4 fast commit wait and wake paths used raw EXT4_STATE bit values even though 64 bit ext4 stores dynamic inode state bits in the upper half of i_flags. This can make the wait key inconsistent with the actual inode state bit used by ext4_test_inode_state and related helpers, which may leave tasks waiting on the wrong synchronization key. The likely impact is local denial of service through stalled fast commit activity, blocked filesystem operations, or degraded system responsiveness. For the CVSS the PR:L is used for the paranoid score because a local unprivileged process that can perform file operations on an affected mounted ext4 filesystem may be enough to exercise the fast commit paths, while administrative privileges are normally required only to enable or mount such a filesystem. The issue is not network reachable and there is no clear memory corruption primitive in the provided diff.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended (with actual score 4)  SKIP CVE-2026-74358 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 857d32f2618166765ce9306a246d0745afc76859 YES  NO NO unknown 	MAYBE	DISK INIT WARNONLY  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local user performing ordinary file operations on an already mounted affected ext4 filesystem can plausibly exercise fast commit paths.

* Reliable kernel crash / strong DoS: +1
  The wrong wait or wake bit can leave tasks waiting on the wrong synchronization key, causing stuck filesystem operations or D state waits.

* Important filesystem/storage path: +1
  ext4 fast commit is part of filesystem journaling and commit handling, so availability regressions affect an important storage path.

* Hard or configuration dependent condition: -1
  The issue is limited to 64 bit mapping of ext4 dynamic inode state bits and requires ext4 fast commit paths to be active.

Paranoid difference:

* Availability impact realistic: +1
  In the higher score, the stuck wait is treated as persistent filesystem level availability degradation rather than a transient local stall.

No memory corruption, UAF, OOB write, page cache corruption, ownership bypass, or privilege escalation primitive is supported by the patch.

## 3. Reachability analysis

The bug is locally reachable through ext4 filesystem activity when fast commit is enabled and the affected wait or wake paths are used. Mounting or enabling the filesystem configuration is administrative, but triggering the affected paths after deployment may only require local write activity by an unprivileged user. Namespaces do not make this remotely reachable, but containers with write access to an affected ext4 backed filesystem could contribute workload that exercises the path. This is not network reachable.

Call-site confidence: high, because the patch shows both wait sites and wake sites in `ext4_fc_del`, `ext4_fc_track_inode`, `ext4_fc_perform_commit`, and `ext4_fc_cleanup`.

## 4. Severity interpretation

This behaves like a borderline actionable Moderate filesystem availability issue, not an Important class vulnerability. The realistic impact is local DoS through stalled fast commit or blocked filesystem operations. The theoretical severity is limited because the patch only fixes wait bit mapping consistency and does not show memory corruption, data corruption, unauthorized write, credential impact, or privilege escalation.

## 5. One-sentence report phrase

An ext4 fast commit wait and wake bit mapping bug on 64 bit systems can cause tasks to wait on the wrong inode state key, potentially stalling filesystem operations and causing a local denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the issue is in an important ext4 journaling path and may cause persistent local filesystem stalls, but there is no evidence of memory corruption, confidentiality impact, integrity impact, or privilege escalation.

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

Patch: ext4: fix fast commit wait/wake bit mapping on 64-bit [ Upstream
Commit: e82d515092a0cf2bca92f399d5c330c324879cea
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e82d515092a0cf2bca92f399d5c330c324879cea

Changed files:
  fs/ext4/ext4.h
  fs/ext4/fast_commit.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=e82d515092a0cf2bca92f399d5c330c324879cea

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

The original Linux kernel CVE announcement for CVE-2026-74358 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74358

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:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 3
  Paranoid ActionableScore: 4

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).