[CVE-2026-46094][MODERATE REGULAR] ext4: fix bounds check in check_xattrs() to prevent out-of-bounds access

[CVE-2026-46094][MODERATE REGULAR] ext4: fix bounds check in check_xattrs() to prevent out-of-bounds access

[AL-KERNEL]

CVE: CVE-2026-46094
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ext4: fix bounds check in check_xattrs() to prevent out-of-bounds access
Commit: ab6da97bc310db35d4e4ef5354bc3ff626b0698c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ab6da97bc310db35d4e4ef5354bc3ff626b0698c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46094
Analysis date: Wed, 27 May 2026 09:54:19 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A malformed ext4 xattr layout can cause check_xattrs() to perform a small out-of-bounds read when IS_LAST_ENTRY() reads 4 bytes near the end of the valid xattr region, requiring local filesystem metadata control and primarily posing a DoS or limited parser-risk concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-46094 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46094

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-2026-46094	MODERATE	CHECK	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:L/A:H';CWE-125;*CWE-20;CWE-119;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.8';DESCR 'An out-of-bounds read in ext4 check_xattrs() can occur because the next xattr entry was only checked against end, while the next loop iteration reads 4 bytes through IS_LAST_ENTRY(). A malformed xattr layout can place the next entry pointer within the last 1 to 3 bytes of the valid xattr region, causing a small overread beyond that region. For the CVSS the PR:L is used in the paranoid score because some environments allow less trusted local users or delegated mount contexts to supply filesystem images, while the realistic default case often requires administrative mount or block device control. The issue is not network reachable and requires local filesystem metadata processing. Impact is at least denial of service or invalid kernel memory read behavior, and in the worst still defensible case may allow limited confidentiality or integrity impact due to parser state confusion, but there is no evidence of an out-of-bounds write or UAF primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 2)	YES	OOB DISK SIMPLEFIX IMPROVEONLY LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	guess

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Important filesystem/storage path: +1
  ext4 xattr metadata validation is a core filesystem metadata path.
* Broad/default/common subsystem: +1
  ext4 is widely deployed.
* Availability impact plausible: +1
  malformed metadata can cause an invalid kernel read and may produce a crash or filesystem error handling path.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2
  reliably supplying malformed ext4 metadata normally requires mounting a crafted filesystem image or controlling the underlying block device.
* Constrained primitive: -1
  the primitive is a small read-only OOB access of up to 3 bytes beyond the valid xattr region, with no OOB write, UAF, double-free, or attacker-controlled overwrite.

Paranoid signals additionally considered:

* Local lower-privilege trigger concern: +1
  in some environments, less trusted users may supply filesystem images through delegated mount workflows, removable media, VM/container storage, or service-managed mount helpers.
* Confidentiality impact weakly plausible: +1
  this is an OOB read in a kernel filesystem parser, but no direct user-visible disclosure path is shown.
* Hard/special precondition: -1
  exploitation requires malformed ext4 xattr metadata and a path that causes the kernel to parse it.

No signals applied for remote reachability, strong LPE, generic strong memory corruption, Dirty-Pipe-like page-cache corruption, or security-boundary bypass.

## 3. Reachability analysis

The bug is triggered when ext4 parses malformed xattr metadata where the computed next xattr entry lands within the last 1 to 3 bytes of the valid xattr region. In ordinary deployments, a local attacker usually needs administrative control over mounting or block device contents to present such metadata to the kernel.

Unprivileged triggering is not the default assumption for normal ext4 use, because ordinary setxattr operations should produce valid layouts. However, delegated mount environments, VM images, container storage workflows, removable media automounting, or service-managed filesystem ingestion can reduce the practical privilege barrier. The path is not network reachable.

## 4. Severity interpretation

This behaves more like a borderline Moderate filesystem parser issue than an Important-class kernel vulnerability. The demonstrated primitive is a limited OOB read, not a write, UAF, double-free, refcount bug, or page-cache ownership violation.

Theoretical concern exists because filesystem metadata parsers run in kernel context and ext4 is broadly deployed. Realistic exploitation evidence is limited to invalid read behavior and possible DoS or error handling effects. There is no strong evidence of privilege escalation.

## 5. One-sentence report phrase

A malformed ext4 xattr layout can cause check_xattrs() to perform a small out-of-bounds read when IS_LAST_ENTRY() reads 4 bytes near the end of the valid xattr region, requiring local filesystem metadata control and primarily posing a DoS or limited parser-risk concern.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the issue is not strong enough for an Important classification based on the patch alone, but it is an OOB read in a widely used kernel filesystem metadata parser, so it should not be blindly auto-closed without confirming mount reachability and deployment exposure.

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

Patch: ext4: fix bounds check in check_xattrs() to prevent out-of-bounds access
Commit: ab6da97bc310db35d4e4ef5354bc3ff626b0698c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ab6da97bc310db35d4e4ef5354bc3ff626b0698c

Commit description:

The bounds check for the next xattr entry in check_xattrs() uses
(void *)next >= end, which allows next to point within sizeof(u32)
bytes of end. On the next loop iteration, IS_LAST_ENTRY() reads 4
bytes via *(__u32 *)(entry), which can overrun the valid xattr region.

For example, if next lands at end - 1, the check passes since
next < end, but IS_LAST_ENTRY() reads 4 bytes starting at end - 1,
accessing 3 bytes beyond the valid region.

Fix this by changing the check to (void *)next + sizeof(u32) > end,
ensuring there is always enough space for the IS_LAST_ENTRY() read
on the subsequent iteration.

Fixes: 3478c83 ("ext4: improve xattr consistency checking and error reporting")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20260224231429.31361-1-kartikey406@gmail.com/T/ [v1]
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
Link: https://patch.msgid.link/20260328150038.349497-1-kartikey406@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/ext4/xattr.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=ab6da97bc310db35d4e4ef5354bc3ff626b0698c

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

The original Linux kernel CVE announcement for CVE-2026-46094 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46094

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 1
  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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).