[CVE-2026-74671][MODERATE 7.0] ima: fix out-of-bounds read in xattr_verify() [ Upstream

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

CVE: CVE-2026-74671
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ima: fix out-of-bounds read in xattr_verify() [ Upstream
Commit: d823b5f4557083d1dd92096f796a78a2b1b06d10
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d823b5f4557083d1dd92096f796a78a2b1b06d10
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74671
Analysis date: Sat, 22 Aug 2026 14:10:07 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A signedness bug in IMA `xattr_verify()` can allow a truncated `security.ima` xattr to bypass a digest length check and cause an OOB read in `memcmp()`, with local DoS risk and limited confidentiality or integrity concern in IMA appraisal workflows.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74671 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74671

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 7.0
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-2026-74671	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-190;CWE-681;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:L';BEST CVSS score: '5.8';DESCR 'An out-of-bounds read in IMA xattr_verify can occur because a digest length check mixes signed int values with size_t from sizeof. A truncated security.ima xattr can make the subtraction underflow to a large unsigned value, bypassing the bounds check and letting memcmp read past the buffer returned by vfs_getxattr_alloc. For the CVSS the PR:L is used for the paranoid score because a local low privileged actor may be able to trigger appraisal of a crafted file if malformed security.ima metadata is already present or can be introduced through a delegated restore, image import, removable media, or writable trusted path. Typical creation of security.ima still requires administrative control, so the base score uses PR:H. The issue is not directly network reachable. Impact is at least a local denial of service risk and in worst case may allow limited confidentiality or integrity impact due to an OOB read in integrity appraisal logic.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	OOB IMPROVEONLY LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Paranoid scoring:

* Local unprivileged trigger: +1
  A low privileged local user may be able to trigger IMA appraisal of a crafted or imported file if the malformed `security.ima` xattr is already present or can enter the system through restore, image import, removable media, or a trusted writable path.

* Memory corruption, weak or indirect corruption candidate: +1
  The primitive is a read past the end of the `vfs_getxattr_alloc()` buffer in `memcmp()`. This is an OOB read, not an OOB write, UAF, double free, or object replacement primitive.

* Confidentiality impact plausible: +1
  There is no direct copy-to-user leak, but an OOB read in a comparison path may create limited observable behavior or comparison-oracle style risk in a security decision path.

* Integrity impact plausible: +1
  The affected code is IMA appraisal logic, so a malformed xattr could potentially affect appraisal decisions in edge cases, even though a reliable bypass is not demonstrated.

* Availability impact realistic: +1
  The OOB read may produce a kernel fault or appraisal failure depending on allocator layout, debug options, and runtime conditions.

* Hard or configuration-dependent triggering: -1
  Reliable exploitation requires a truncated `security.ima` xattr to reach the appraisal path. Creating such xattrs is usually privileged.

Conservative scoring:

* OOB read in kernel security path: +1
* Limited availability or appraisal impact: +1
* Important integrity appraisal path: +1
* Requires administrative control to create `security.ima` in typical deployments: -2
* Conservative total: 2

## 3. Reachability analysis

The bug is local, not network reachable. In normal deployments, creating or modifying `security.ima` xattrs requires administrative privileges or a trusted signing or restore path, so the conservative trigger is PR:H-like. The paranoid interpretation uses a lower privilege model because an unprivileged user may only need to access a file after malformed metadata has already been introduced by backup restore, filesystem image import, removable media, or another delegated workflow.

Namespaces and containers usually do not make this broadly unprivileged, because real `security.ima` manipulation is not normally delegated to ordinary container users. The affected path also depends on IMA appraisal being enabled and policy-relevant for the accessed file, so it is not a universal default exposure.

Call-site confidence: medium-high. The changed check and the following `memcmp()` sink are directly shown, but broader deployment-specific IMA policy reachability is not fully available from the patch alone.

## 4. Severity interpretation

This is not an Important-class issue by default because the demonstrated primitive is a limited OOB read, with no OOB write, UAF, arbitrary write, type confusion, or attacker-controlled reclaim. It is stronger than an ordinary low-priority cleanup because the OOB read occurs in IMA appraisal code and can affect a security-relevant decision path.

Realistically, this behaves like an ordinary Moderate in typical locked-down deployments. Under the paranoid but defensible model, it becomes Actionable Moderate because local low-privileged triggering may be possible through preexisting malformed metadata and the bug sits in integrity enforcement logic.

## 5. One-sentence report phrase

A signedness bug in IMA `xattr_verify()` can allow a truncated `security.ima` xattr to bypass a digest length check and cause an OOB read in `memcmp()`, with local DoS risk and limited confidentiality or integrity concern in IMA appraisal workflows.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

YES REQUIRES MANUAL CHECK because this is an OOB read in Linux integrity appraisal code, and the practical risk depends heavily on IMA policy, EVM configuration, and whether malformed `security.ima` metadata can be introduced without full host-root control.

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UPSTREAM PATCH SUMMARY
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Patch: ima: fix out-of-bounds read in xattr_verify() [ Upstream
Commit: d823b5f4557083d1dd92096f796a78a2b1b06d10
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d823b5f4557083d1dd92096f796a78a2b1b06d10

Changed files:
  security/integrity/ima/ima_appraise.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=d823b5f4557083d1dd92096f796a78a2b1b06d10

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

The original Linux kernel CVE announcement for CVE-2026-74671 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74671

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:L/I:L/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: 2
  Paranoid ActionableScore: 5

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 7.0

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).