[CVE-2026-68448][MODERATE 7.0] ovl: check access to copy_file_range source with src mounter creds [ Upstream

[CVE-2026-68448][MODERATE 7.0] ovl: check access to copy_file_range source with src mounter creds [ Upstream

[AL-KERNEL]

CVE: CVE-2026-68448
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ovl: check access to copy_file_range source with src mounter creds [ Upstream
Commit: 9ec22c8113d8cf72ed7197bb61037dcad09e50d8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9ec22c8113d8cf72ed7197bb61037dcad09e50d8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68448
Analysis date: Tue, 11 Aug 2026 21:52:06 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
An overlayfs cross-sb `copy_file_range()` permission bypass could validate source read access with destination mounter credentials, allowing a local user in a suitable overlayfs configuration to copy file data that the source mount policy should deny.

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

The original Linux kernel CVE announcement for CVE-2026-68448 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68448

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-68448	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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:N';CWE-863;CWE-284;*CWE-200;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N';BEST CVSS score: '5.5';DESCR 'A read permission bypass in overlayfs can occur during cross-sb copy_file_range because the source read access check may be evaluated with the destination overlayfs mounter credentials instead of the source overlayfs mounter credentials. A local user who can access suitable overlayfs mounts may be able to copy data from a source file that should otherwise be denied by the source mount policy. For the CVSS the PR:L is used because triggering requires local code execution or a local process able to invoke copy_file_range on the affected mounts, but it does not normally require full administrator privileges once the vulnerable mount layout exists. The issue is not network reachable and is triggered through a local filesystem operation. Impact is confidentiality loss due to unauthorized file read or copy, with no direct evidence of memory corruption, kernel crash, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	DISK HARDWARE LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	NO	NO	guess

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local process can invoke `copy_file_range()` if it has access to the involved overlayfs files and the vulnerable mount layout already exists.

* Security-boundary bypass with practical sensitive-object access: +2
  The bug is an access-control error. Source read permission for cross-sb overlayfs copy may be checked with destination mounter credentials instead of source mounter credentials, allowing reads that should be denied by the source overlayfs policy.

* Confidentiality impact plausible: +1
  The direct impact is unauthorized read or copy of file contents.

* Important filesystem/storage path: +1
  The issue is in overlayfs copy handling, a common filesystem path especially in container and layered filesystem deployments.

Subtracted signals:

* Specific cross-sb overlayfs setup required: -1
  The bug requires two overlayfs superblocks and differing mounter-credential behavior. It is not a generic local file read bypass on all overlayfs copies.

Paranoid-only signal:

* Practical exploit chain strongly implied: +1
  The commit explicitly states that the bug can allow read access to a file that would otherwise be denied. This is a concrete permission-bypass consequence, not merely theoretical filesystem inconsistency.

## 3. Reachability analysis

The trigger is local. An attacker needs a process able to call `copy_file_range()` on files from suitable overlayfs mounts. The attacker does not necessarily need full administrator privileges once the affected overlayfs layout exists, but creating that layout may require privileged mount setup in many deployments.

Namespaces and containers matter. Overlayfs is common in container stacks, and reduced-privilege root or container-managed overlayfs configurations may make this more relevant than a pure host-root-only issue. However, the vulnerable condition still depends on cross-sb overlayfs copying and mismatched source versus destination mounter credentials.

The path is not network reachable. It is a local filesystem control/data path issue.

## 4. Severity interpretation

This behaves like an actionable Moderate confidentiality and policy-bypass issue, not like a memory-corruption or kernel-crash issue.

There is no evidence of UAF, OOB access, arbitrary write, kernel crash, or privilege escalation. The important security property is that overlayfs may apply the wrong credential context when verifying source read access during cross-sb `copy_file_range()`. That can expose data that should be denied by the source mount policy.

Conservative handling can be score 4 because the setup is specific. Paranoid handling reaches score 5 because the permission bypass and unauthorized read consequence are explicitly supported by the patch context.

## 5. One-sentence report phrase

An overlayfs cross-sb `copy_file_range()` permission bypass could validate source read access with destination mounter credentials, allowing a local user in a suitable overlayfs configuration to copy file data that the source mount policy should deny.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is not memory corruption, but it is a concrete filesystem permission bypass with plausible unauthorized file disclosure. The practical risk depends on overlayfs deployment details, mounter credentials, namespaces, and whether sensitive source files are reachable through the affected cross-sb copy path.

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

Patch: ovl: check access to copy_file_range source with src mounter creds [ Upstream
Commit: 9ec22c8113d8cf72ed7197bb61037dcad09e50d8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9ec22c8113d8cf72ed7197bb61037dcad09e50d8

Changed files:
  fs/overlayfs/file.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=9ec22c8113d8cf72ed7197bb61037dcad09e50d8

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

The original Linux kernel CVE announcement for CVE-2026-68448 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68448

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:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 5.5

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: 4
  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: YES
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).