[CVE-2026-68149][MODERATE 7.0] fs: preserve ACL_DONT_CACHE state in forget_cached_acl()

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

CVE: CVE-2026-68149
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: fs: preserve ACL_DONT_CACHE state in forget_cached_acl()
Commit: b98fad81f1202b0eb26aacf3ff4cc7a21ed3b5bf
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b98fad81f1202b0eb26aacf3ff4cc7a21ed3b5bf
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68149
Analysis date: Mon, 10 Aug 2026 20:16:46 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-68149 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68149

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-2026-68149	MODERATE	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-863;CWE-285;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N';BEST CVSS score: '6.3';DESCR 'A stale ACL authorization issue can occur because forget_cached_acl can accidentally replace ACL_DONT_CACHE with ACL_NOT_CACHED and enable POSIX ACL caching for an inode that explicitly opted out. On FUSE filesystems where FUSE_POSIX_ACL was not negotiated, this can make get_acl return a stale cached ACL value because set_acl does not invalidate that unintended cache state. For the CVSS the PR:L value is used for the paranoid score because a local user or local process with access to the affected mount can trigger permission checks, while full administrator privileges are not inherently required for the vulnerable access path. The issue is not directly network reachable from the kernel perspective, although the backing FUSE service may itself use remote storage. Impact is an access control bypass with possible confidentiality and integrity impact on files protected by ACLs, not a kernel crash or memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 6)	YES	DISK IMPROVEONLY LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5

1. ActionableScore
* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**

2. Signal breakdown
* Local unprivileged trigger: +1. A local process with access to the affected FUSE mount can trigger ACL lookups through normal filesystem operations.
* Security-boundary bypass with practical sensitive-object access: +2. The bug can make get_acl return a stale cached ACL value on a filesystem that explicitly opted out of ACL caching, which can bypass intended POSIX ACL authorization.
* Confidentiality impact plausible: +1. A stale permissive ACL may allow reading files that should no longer be readable.
* Integrity impact plausible: +1. A stale permissive ACL may allow writing or modifying files that should no longer be writable.
* Important filesystem access-control path: +1. The affected helper is in the VFS POSIX ACL cache path and impacts FUSE ACL authorization behavior.
* Hard timing or state dependency: -1. The issue requires a specific sequence where ACL_DONT_CACHE is lost and a later get_acl observes stale cached state.

Paranoid delta: +1 because the affected code is a generic VFS ACL helper and stale ACLs on shared or service-backed FUSE mounts can protect sensitive objects, even though there is no memory corruption.

3. Reachability analysis
The bug is locally reachable through filesystem operations on an affected FUSE filesystem where FUSE_POSIX_ACL was not negotiated and ACL_DONT_CACHE should remain persistent. Mount setup may require policy-dependent privileges, but triggering permission checks on an already available mount can be done by a local user or service process. Containers or user namespaces may matter if FUSE mounts are delegated into the container or if a service exposes a shared FUSE mount. This is not directly network reachable from the kernel perspective, although the FUSE backend may be remote.

4. Severity interpretation
This is not a memory corruption issue and does not show UAF, OOB access, arbitrary write, or kernel code execution potential. It behaves as an authorization and cache-invalidation bug that can produce stale ACL decisions. Realistic impact is confidentiality and integrity bypass on files protected by POSIX ACLs, not DoS or LPE. Because it affects access-control correctness, it should not be treated as an ordinary low-risk functional bug.

5. One-sentence report phrase
A stale ACL authorization issue can occur because forget_cached_acl may clear ACL_DONT_CACHE and unintentionally enable POSIX ACL caching for FUSE inodes, allowing get_acl to return stale permissions and potentially bypass file access restrictions.

6. Manual review recommendation
MANUAL CHECK REQUIRED. This is an access-control bypass candidate with plausible confidentiality and integrity impact on ACL-protected files, and environment-specific FUSE deployment details determine practical severity.

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

Patch: fs: preserve ACL_DONT_CACHE state in forget_cached_acl()
Commit: b98fad81f1202b0eb26aacf3ff4cc7a21ed3b5bf
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b98fad81f1202b0eb26aacf3ff4cc7a21ed3b5bf

Commit description:

The ACL_DONT_CACHE state is meant to be a constant state for the inode
for filesystems that want to opt out of posix acl caching.

Commit facd610 ("fuse: fixes after adapting to new posix acl api")
used this facility to opt out of posix acl caching for fuse inodes with
fuse server that does not negotiate FUSE_POSIX_ACL (fc->posix_acl).

The commit also takes care to gate the forget_all_cached_acls() call in
fuse_set_acl() on fc->posix_acl because there is no need for it, but
there are other placed in fuse code which call forget_all_cached_acls()
unconditional to fc->posix_acl and those cause the loss of the
ACL_DONT_CACHE state.

This is not only a functional bug. Properly timed, a get_acl() from this
fuse filesystem can return a stale cached value, as was observed in tests,
because set_acl() does not invalidate the unintentional acl cache.

We could fix this in fuse, but it actually makes no sense for the vfs
helper forget_cached_acl() to invalidate the ACL_DONT_CACHE state, so
let it not do that to fix fuse and future users of ACL_DONT_CACHE.

Fixes: facd610 ("fuse: fixes after adapting to new posix acl api")
Cc: stable@vger.kernel.org
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://patch.msgid.link/20260713220932.413004-2-amir73il@gmail.com
Reviewed-by: Luis Henriques <luis@igalia.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/posix_acl.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=b98fad81f1202b0eb26aacf3ff4cc7a21ed3b5bf

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

The original Linux kernel CVE announcement for CVE-2026-68149 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68149

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: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: 5
  Paranoid ActionableScore: 6

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).