[CVE-2026-74399][MODERATE REGULAR] evm: terminate and bound the evm_xattrs read buffer [ Upstream

[CVE-2026-74399][MODERATE REGULAR] evm: terminate and bound the evm_xattrs read buffer [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74399
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: evm: terminate and bound the evm_xattrs read buffer [ Upstream
Commit: 8df81954d22a653a8b01d46692cd56f71137269b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8df81954d22a653a8b01d46692cd56f71137269b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74399
Analysis date: Sun, 16 Aug 2026 02:29:22 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline manual review recommended / Ordinary Moderate with information disclosure risk
Manual review required: YES

Summary:
An EVM securityfs read path can call `strlen()` on an uninitialized and unterminated buffer when no xattrs are enabled, allowing a local reader to potentially disclose adjacent kernel heap data.

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

The original Linux kernel CVE announcement for CVE-2026-74399 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74399

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-2026-74399	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:L';CWE-125;*CWE-457;*CWE-200;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '6.1';DESCR 'An out of bounds read in the EVM securityfs xattrs read path can occur because evm_read_xattrs uses strlen on a newly allocated buffer that may remain uninitialized when no configured xattrs are enabled. The resulting length can then be used by simple_read_from_buffer, so a local reader may receive uninitialized or adjacent kernel heap bytes. For the CVSS the PR:L is used because a local process that can read the EVM securityfs xattrs file can trigger the flawed read path. If the file is restricted to administrator only on a given system, the practical PR may be higher. The issue is not network reachable and does not provide a direct write primitive. Impact is primarily information disclosure with possible limited availability impact if the over read hits debug checks or invalid memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Ordinary Moderate with information disclosure risk (with actual score 3)	YES	SIMPLEFIX  INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline manual review recommended / Ordinary Moderate with information disclosure risk**::

## 2. Signal breakdown

* Local trigger: +1. The bug is reachable by reading the EVM securityfs xattrs interface, assuming the local user or local service has read access to that node.
* Confidentiality impact plausible: +1. `strlen(temp)` can read past initialized data, and `simple_read_from_buffer()` may then copy uninitialized or adjacent kernel heap bytes to userspace.
* Availability impact realistic in paranoid scoring: +1. The unbounded read can theoretically hit hardened allocator checks or invalid memory in debug or hardened configurations, but a reliable production crash is not demonstrated.
* No generic memory corruption bonus. This is an out-of-bounds read / uninitialized read, not UAF, double free, OOB write, arbitrary write, or type confusion.
* No LPE bonus. The patch does not show attacker-controlled overwrite, reclaim, callback control, refcount abuse, or another privilege escalation primitive.
* No network bonus. The affected path is local securityfs/EVM control or read path, not packet or remote protocol parsing.

## 3. Reachability analysis

A local process that can read the EVM xattrs securityfs file can trigger the flawed read path. Practical reachability depends on whether securityfs is mounted, EVM support is enabled, and the relevant file permissions allow non-admin reads. Containers and namespaces usually do not automatically expose this interface unless securityfs is mounted or delegated, so the trigger is local and configuration dependent. The vulnerable condition requires no configured xattrs to be enabled, causing the allocated buffer to remain unterminated before `strlen()`.

Call-site confidence: high. The patch shows the full affected read path, the uninitialized buffer condition, the `strlen()` use, and the user-copy sink through `simple_read_from_buffer()`.

## 4. Severity interpretation

This behaves like an information disclosure issue rather than a strong memory corruption or LPE issue. The theoretical risk is kernel heap disclosure from an out-of-bounds read, which can matter for bypassing mitigations or leaking sensitive adjacent data. Realistic exploitation depends heavily on permissions, heap contents, and whether the file is accessible to non-admin local users. This is not an Important-class candidate by itself, but it should not be blindly auto-closed without checking product permissions and EVM/securityfs exposure.

## 5. One-sentence report phrase

An EVM securityfs read path can call `strlen()` on an uninitialized and unterminated buffer when no xattrs are enabled, allowing a local reader to potentially disclose adjacent kernel heap data.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a concrete out-of-bounds read with a possible kernel memory disclosure path. Manual review should verify the securityfs file permissions, whether unprivileged or reduced-privilege users can read it, and whether the affected product enables EVM/securityfs by default.

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

Patch: evm: terminate and bound the evm_xattrs read buffer [ Upstream
Commit: 8df81954d22a653a8b01d46692cd56f71137269b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8df81954d22a653a8b01d46692cd56f71137269b

Changed files:
  security/integrity/evm/evm_secfs.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=8df81954d22a653a8b01d46692cd56f71137269b

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

The original Linux kernel CVE announcement for CVE-2026-74399 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74399

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:L/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:L
  The Best / paranoid CVSS score: 6.1

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: 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).