[CVE-2026-64375][IMPORTANT] proc: protect ptrace_may_access() with exec_update_lock (FD links) [ Upstream

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

CVE: CVE-2026-64375
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: proc: protect ptrace_may_access() with exec_update_lock (FD links) [ Upstream
Commit: 6253dfee5afba536bb54fc6fe6c091c3758fafe1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6253dfee5afba536bb54fc6fe6c091c3758fafe1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64375
Analysis date: Sat, 25 Jul 2026 12:26:11 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A TOCTOU race in procfs link handling can separate `ptrace_may_access()` from the task used to resolve `/proc/pid/fd` and related links, allowing a local attacker to potentially bypass procfs access controls and inspect or access sensitive process resources.

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

The original Linux kernel CVE announcement for CVE-2026-64375 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64375

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: IMPORTANT
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-2026-64375	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N';CWE-367;CWE-362;CWE-863;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N';BEST CVSS score: '6.3';DESCR 'A TOCTOU race in procfs link handling can separate the ptrace_may_access authorization check from the task used to resolve /proc/pid/fd cwd root exe or map_files links. A local user can try to race a task through exec so the access check is made against one credential or exec state while the link target is resolved after the state has changed. For the CVSS the PR:L because reliable triggering requires local code execution or control of a local process that can drive procfs lookups and exec timing. The issue is not network reachable and is triggered through local procfs operations. Impact is mainly unauthorized access to proc link targets or file descriptor magic links, with possible confidentiality and integrity impact if the race exposes privileged process resources. For the paranoid score, choose the highest still defensible interpretation supported by the access control race and procfs fd context, with preference for manual-review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-64375 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 778c1144771f0064b6f51bee865cceb0d996f2f9 YES  NO NO unknown 	MAYBE	DISK IMPROVEONLY LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  Local users can access procfs paths such as `/proc/pid/fd`, `/proc/pid/cwd`, `/proc/pid/root`, `/proc/pid/exe`, and `map_files` subject to ptrace-style checks.

* Security-boundary bypass with practical sensitive-object access: +2
  The bug is a TOCTOU race between `ptrace_may_access()` and the actual procfs link resolution. This is an intended Linux security boundary.

* Sensitive file / credential / file-descriptor theft primitive: +2
  The affected path includes `/proc/pid/fd` magic links. If the race is won, it may expose file descriptors or paths belonging to a process state that should not have passed the ptrace access check.

* Practical exploit chain strongly implied: +1
  The patch specifically fixes the separation between access check and object resolution by locking with `exec_update_lock`, which strongly implies a real authorization-race chain around exec state changes.

* Confidentiality impact plausible: +1
  Unauthorized procfs link resolution can disclose paths, executable state, cwd/root, map files, or potentially sensitive file descriptor targets.

* Integrity impact plausible: +1
  If a writable privileged fd or special fd is exposed through `/proc/pid/fd`, this can become more than read-only disclosure.

* Hard or unreliable race / special timing required: -1
  Exploitation requires racing procfs access with exec-related task state changes.

Not counted:

* Generic memory corruption: +0
  The patch does not show UAF, OOB write, double free, arbitrary write, or type confusion.

* Reliable kernel crash / strong DoS: +0
  The main issue is access-control TOCTOU, not crash or resource exhaustion.

Call-site confidence: high. The patch shows both the access check and the affected call sites for `proc_pid_get_link()`, `proc_pid_readlink()`, and fd/cwd/root/exe/map_files link handlers.

## 3. Reachability analysis

A local user can trigger the relevant procfs operations without needing network access. The realistic attacker needs local code execution and the ability to coordinate procfs lookups with task exec timing, so PR is effectively local unprivileged rather than remote or admin-only.

Namespaces and reduced privilege models matter. Container root, uid 0 without `CAP_SYS_PTRACE`, sandboxed service accounts, or processes relying on ptrace and dumpability boundaries may be affected because the bug targets exactly this kind of permission boundary.

The affected procfs functionality is broadly available on normal Linux systems. The exploit condition is race-dependent, but the subsystem and access pattern are common.

## 4. Severity interpretation

This behaves more like an Important-class security-boundary bypass candidate than an ordinary Moderate correctness bug. It is not memory corruption, and there is no demonstrated arbitrary write or kernel code execution primitive in the patch. However, procfs fd magic links and ptrace permission checks are security-sensitive, and bypassing them can plausibly expose privileged process resources.

The conservative score is Actionable Moderate because exploitation requires a race. The paranoid score reaches Strong Important candidate because the affected object class includes privileged fd links and procfs task state, where confidentiality and integrity consequences can be significant.

## 5. One-sentence report phrase

A TOCTOU race in procfs link handling can separate `ptrace_may_access()` from the task used to resolve `/proc/pid/fd` and related links, allowing a local attacker to potentially bypass procfs access controls and inspect or access sensitive process resources.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should not be auto-closed because it is a local procfs authorization race affecting ptrace-protected fd and task-state links, with plausible sensitive fd exposure and security-boundary bypass impact even without memory corruption.

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

Patch: proc: protect ptrace_may_access() with exec_update_lock (FD links) [ Upstream
Commit: 6253dfee5afba536bb54fc6fe6c091c3758fafe1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6253dfee5afba536bb54fc6fe6c091c3758fafe1

Changed files:
  fs/proc/base.c
  fs/proc/fd.c
  fs/proc/internal.h

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=6253dfee5afba536bb54fc6fe6c091c3758fafe1

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

The original Linux kernel CVE announcement for CVE-2026-64375 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64375

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:H/I:L/A:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
  The Best / paranoid CVSS score: 6.3

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: 6
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).