[CVE-2026-92499][MODERATE REGULAR] ext4: validate readdir offset before accessing dirent [ Upstream

[CVE-2026-92499][MODERATE REGULAR] ext4: validate readdir offset before accessing dirent [ Upstream

[AL-KERNEL]

CVE: CVE-2026-92499
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ext4: validate readdir offset before accessing dirent [ Upstream
Commit: 64d445d40e5ea4c4d4d88880db753b370cb69161
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=64d445d40e5ea4c4d4d88880db753b370cb69161
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92499
Analysis date: Fri, 18 Sep 2026 08:38:32 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-92499 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92499

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-2026-92499	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-92499 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:L/I:N/A:H';CWE-125;*CWE-416;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'An out of bounds read in ext4_readdir can occur when a corrupted directory record length causes readdir to resume from an offset too close to the end of a directory block. The next directory entry is truncated, but __ext4_check_dir_entry may still read de rec_len before the range is validated, and KASAN can report this as a use after free when the read lands in an adjacent freed page. For the CVSS the PR:L is used because a local user may be able to trigger getdents on an already mounted corrupted ext4 filesystem, while creating or mounting the malformed filesystem often requires higher privileges in typical deployments. The issue is not network reachable and requires local filesystem access plus a malformed ext4 directory, so AC:H is used. Impact is at least local denial of service via kernel crash or KASAN panic. A limited confidentiality impact is kept only in the paranoid score because the primitive is an invalid kernel read, but the patch context does not show a direct user visible information leak or any write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	READ OOB DANGER DISK UAF SYZBOT  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline / manual review recommended**::

No floor or cap changed the conservative score. No floor or cap changed the paranoid score.

2. Signal breakdown

Conservative positive signals:

* +1 Limited OOB read / invalid structured read. ext4_readdir can pass an offset too close to the end of the directory block, and __ext4_check_dir_entry may read de rec_len before the complete dirent range is validated.
* +1 Reliable kernel crash / strong DoS. The supplied KASAN trace shows a kernel fault in __ext4_check_dir_entry reached through getdents64.
* +1 Important filesystem path. The bug is in ext4 directory iteration, a core filesystem path for a broadly used filesystem.

Paranoid additional signal:

* +1 Local below-admin trigger is plausible in the narrower trigger phase. A local user with access to an already mounted corrupted ext4 directory can call getdents/readdir and reach the vulnerable path.

Non-awarded signals:

* RealUAF not awarded. The commit explicitly says KASAN reports use-after-free because the OOB read lands in an adjacent freed page, while the directory buffer itself is still referenced.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality not awarded. The primitive is an internal kernel OOB read, but no user-visible disclosure path is shown.
* Integrity not awarded. There is no write primitive and no demonstrated filesystem ownership or metadata modification caused by the bug.
* Extra Availability not awarded because the same crash is already counted once.
* Remote reachability not established.
* Strong LPE or strong exploitation leverage not awarded.
* No concrete repeated release/refcount operation exists.
* No Floor 5 applied because there is no real UAF, no second lifetime mutation, and no meaningful exploitation surface beyond invalid read/crash.

Negative signals:

* No -2 host-admin penalty applied. Host-admin-equivalent privilege is not positively established for merely triggering readdir on an already mounted corrupted filesystem.
* No -1 race/timing penalty applied. This is not a timing race.
* No rare-subsystem penalty applied. ext4 is common, although the malformed directory prerequisite limits practical reachability.

3. Reachability analysis

The immediate vulnerable operation is local filesystem access through ext4_readdir, reachable via getdents64/readdir on a mounted ext4 filesystem. If a corrupted directory is already mounted and accessible, an ordinary local user may trigger the fault by reading that directory.

The unresolved prerequisite is how the attacker obtains or introduces the corrupted ext4 directory. Creating or mounting a crafted malformed ext4 filesystem commonly requires host-admin-equivalent privilege or a privileged mount path, but the supplied evidence does not prove that host admin is always required for the complete scenario. Therefore HostAdminRequired is UNKNOWN rather than YES.

There is no network path in the supplied patch. Namespace-scoped privilege is not relevant and is set to NO. No special hardware is required. No race repeatability issue is involved.

4. Primitive and severity interpretation

The exact primitive is a bounds-checking failure in ext4 directory iteration that permits a read of de rec_len from a truncated directory entry crossing the end of a block. This is best interpreted as a limited OOB read / invalid structured read, not as a real UAF.

The demonstrated consequence is kernel crash or KASAN panic. The speculative consequence would be limited information exposure from an invalid read, but no path is shown where the read bytes are returned to userspace or otherwise disclosed. There is no write primitive, no lifetime/refcount mutation, no controlled reclaim, and no authorization boundary bypass.

PrimitiveClass is CLASS_C because the established behavior is primarily crash/DoS from invalid read behavior. ImportantCandidate is NO because there is no concrete corruption, ownership, lifetime, or boundary primitive needing Important-vs-Moderate preservation. AutoDowngradeAllowed is YES because the issue appears suitable for ordinary Moderate handling after manual confirmation of affected deployments and attacker control over malformed filesystem exposure.

Operationally, this is a local DoS risk for systems that mount or expose corrupted ext4 filesystems to less-privileged users.

5. One-sentence report phrase

A corrupted ext4 directory can cause ext4_readdir to resume from an invalid offset and read a truncated dirent past the end of a block, leading to a local kernel crash through getdents on an affected mounted filesystem.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The issue is probably DoS-only, but manual review is recommended because the KASAN report labels the symptom as UAF and the practical risk depends on whether an unprivileged local attacker can access or supply a malformed mounted ext4 filesystem in the evaluated environment.

7. Call-site confidence

Call-site confidence: high

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

Patch: ext4: validate readdir offset before accessing dirent [ Upstream
Commit: 64d445d40e5ea4c4d4d88880db753b370cb69161
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=64d445d40e5ea4c4d4d88880db753b370cb69161

Changed files:
  fs/ext4/dir.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=64d445d40e5ea4c4d4d88880db753b370cb69161

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

The original Linux kernel CVE announcement for CVE-2026-92499 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92499

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:H/PR:L/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 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).