[CVE-2026-64544][LOW] crypto: asymmetric_keys - fix OOB read in pefile_digest_pe_contents [ Upstream

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

CVE: CVE-2026-64544
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: crypto: asymmetric_keys - fix OOB read in pefile_digest_pe_contents [ Upstream
Commit: 89efd998470a93284b7ad5a20d4e0e3c6858ae8e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=89efd998470a93284b7ad5a20d4e0e3c6858ae8e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64544
Analysis date: Wed, 29 Jul 2026 02:26:11 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A crafted PE image processed through the privileged kexec signature verification path can trigger an OOB read in pefile_digest_pe_contents() and crash the kernel, with no demonstrated write primitive or unprivileged reachability.

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

The original Linux kernel CVE announcement for CVE-2026-64544 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64544

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: LOW
Manual review required: NO

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
======================================================================

CVE-2026-64544	LOW	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H';CWE-125;CWE-190;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.1';DESCR 'An out of bounds read in PE file digesting can occur because pefile_digest_pe_contents computes the trailing data length from pelen minus hashed_bytes plus certs_size without first validating that the addition fits inside pelen. A crafted PE image can make the unsigned subtraction underflow and pass a very large length to crypto_shash_update, causing the hash code to read beyond the vmalloc buffer and hit a guard page. For the CVSS the PR:H is used because the observed call path is kexec_file_load and reliable triggering normally requires CAP_SYS_BOOT or equivalent administrative control over kexec image loading. The issue is not network reachable and requires local control of the PE image supplied to kernel signature verification. Impact is primarily denial of service via kernel panic. For the paranoid score, C:L is kept because the primitive is an out of bounds read, but no practical data disclosure channel or write primitive is evident from the code path.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1) 	MAYBE	KASAN OOB LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Triggered signals:

* Reliable kernel crash / strong DoS: +1
  The crafted PE can make the unsigned length underflow and cause crypto_shash_update() to read into unmapped vmalloc guard pages, producing a kernel panic.

* Availability impact realistic: +1
  The demonstrated result is a host-wide panic, but this is not additionally escalated beyond DoS because the path is privileged.

* Confidentiality impact plausible, paranoid only: +1
  The primitive is an OOB read into the hashing path, but there is no clear user-visible disclosure channel. This supports only a weak paranoid C concern.

Subtracted signals:

* Requires admin/root/CAP_* in typical deployments: -2
  The observed call path is kexec_file_load(), which normally requires CAP_SYS_BOOT or equivalent administrative control.

Not applied:

* No remote reachability.
* No local unprivileged trigger.
* No write primitive.
* No UAF, double-free, refcount takeover, object replacement, or type confusion.
* No practical privilege escalation path is shown.

Call-site confidence: high. The stack trace shows the relevant path through verify_pefile_signature() and kexec_file_load().

## 3. Reachability analysis

The realistic trigger is a local privileged user supplying a crafted PE image to kernel PE signature verification through kexec_file_load(). In typical deployments this requires CAP_SYS_BOOT or equivalent root-level authority. Namespaces do not usually make this reachable to an unprivileged container user, because kexec loading is host-global and privileged. The path is not network reachable and does not appear default-exposed to ordinary users.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like privileged DoS issue rather than an Important-class kernel vulnerability. The theoretical primitive is an OOB read, but the demonstrated effect is a panic on guard-page access, not controlled data disclosure or memory corruption. Because the attacker already needs high privileges to reach the kexec path, practical security impact is limited.

## 5. One-sentence report phrase

A crafted PE image processed through the privileged kexec signature verification path can trigger an OOB read in pefile_digest_pe_contents() and crash the kernel, with no demonstrated write primitive or unprivileged reachability.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a privileged local kexec-path DoS with only weak theoretical confidentiality concern and no evidence of LPE, remote reachability, or strong memory corruption.

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

Patch: crypto: asymmetric_keys - fix OOB read in pefile_digest_pe_contents [ Upstream
Commit: 89efd998470a93284b7ad5a20d4e0e3c6858ae8e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=89efd998470a93284b7ad5a20d4e0e3c6858ae8e

Changed files:
  lib/crypto/sha256.c
  crypto/sha256.c
  crypto/asymmetric_keys/verify_pefile.c
  kernel/kexec_file.c
  arch/x86/entry/syscall_64.c
  arch/x86/entry/entry_64.S

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=89efd998470a93284b7ad5a20d4e0e3c6858ae8e

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

The original Linux kernel CVE announcement for CVE-2026-64544 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64544

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:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 5.1

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: 0
  Paranoid ActionableScore: 1

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).