From: AL-KERNEL <[email protected]>
To: [email protected]
Subject: [CVE-2026-53311][LOW] fuse: fix uninit-value in fuse_dentry_revalidate()
Date: Fri, 26 Jun 2026 16:05:58 -0400 [thread overview]
Message-ID: <[email protected]> (raw)
CVE: CVE-2026-53311
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: fuse: fix uninit-value in fuse_dentry_revalidate()
Commit: da3d241c5b925f17a9d8051d7a9e0d454d8e01f6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=da3d241c5b925f17a9d8051d7a9e0d454d8e01f6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53311
Analysis date: Fri, 26 Jun 2026 16:05:58 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO
Summary:
FUSE dentry revalidation could read an uninitialized dentry d_time value during local pathname lookup, causing cache validation decisions to depend on stale allocator contents with limited integrity impact and no demonstrated memory corruption primitive.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-53311 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53311
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-53311 LOW CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L';*CWE-457;CWE-665;CWE-754;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'FUSE dentry revalidation can read an uninitialized dentry d_time value when a newly allocated dentry reaches fuse_dentry_revalidate through the lookup_open path. The value is used in cache invalidation logic against the FUSE epoch, so an uninitialized value can make the dentry validation decision depend on stale allocator contents rather than a defined initial state. For the CVSS the PR:L is used because a local user or process must access a FUSE mount or otherwise trigger local pathname lookup activity. The issue is not network reachable. Impact is mainly a limited integrity concern from incorrect dentry cache validation, with possible limited availability impact in debug or sanitizer builds. There is no clear UAF, OOB access, arbitrary write, or direct information leak primitive supported by the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) SKIP CVE-2026-53311 SKIP The Fixes patch not applied yet, so unlikely that actual: 2396356a945bb022aff02656f59c2a45d457043f YES NO NO unknown MAYBE READ KASAN DISK INIT NOMEMCHK LINUS SYZBOT - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
## 1. ActionableScore
* Conservative score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::
## 2. Signal breakdown
* Local unprivileged trigger: +1
A local user or process can plausibly trigger pathname lookup activity on a FUSE mount.
* Integrity impact plausible: +1
The uninitialized `dentry->d_time` value can affect FUSE dentry cache revalidation decisions, potentially causing incorrect cache validity behavior.
* No generic memory corruption: +0
The patch shows initialization of a scalar dentry timestamp field, not UAF, OOB write, double-free, type confusion, or arbitrary write.
* No reliable kernel crash / strong DoS: +0
The issue was detected by KMSAN as an uninitialized value read. The patch does not indicate a production kernel panic path.
* No confidentiality primitive: +0
There is no user-visible leak of the uninitialized value.
* No Important filesystem metadata corruption signal: +0
This affects FUSE dentry validation state, not persistent filesystem metadata or page-cache ownership.
## 3. Reachability analysis
A local process needs access to a FUSE mount and must trigger lookup/open paths that create and revalidate a newly allocated dentry. This is not network reachable. User namespaces may make FUSE usage more common in containerized or desktop-like environments, but the bug still requires local filesystem activity rather than remote input. FUSE is common, but this specific issue is a local cache-validation logic bug with no demonstrated corruption primitive.
## 4. Severity interpretation
This behaves like an ordinary Moderate or Low-like issue rather than an Important-class kernel vulnerability. The theoretical impact is incorrect FUSE dentry cache validation caused by use of an uninitialized scalar field. Realistic exploitation evidence supports limited integrity impact at most, not privilege escalation, memory corruption, or sensitive data disclosure.
## 5. One-sentence report phrase
FUSE dentry revalidation could read an uninitialized dentry d_time value during local pathname lookup, causing cache validation decisions to depend on stale allocator contents with limited integrity impact and no demonstrated memory corruption primitive.
## 6. Manual review recommendation
NO MANUAL CHECK NEEDED
This can be auto-closed for urgent triage purposes because the ActionableScore is below 3, the best CVSS hint is 4.4, and the patch context supports only a local uninitialized scalar logic bug without UAF, OOB access, arbitrary write, info leak, or realistic LPE path.
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: fuse: fix uninit-value in fuse_dentry_revalidate()
Commit: da3d241c5b925f17a9d8051d7a9e0d454d8e01f6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=da3d241c5b925f17a9d8051d7a9e0d454d8e01f6
Commit description:
fuse_dentry_revalidate() may be called with a dentry that didn't had
->d_time initialised. The issue was found with KMSAN, where lookup_open()
calls __d_alloc(), followed by d_revalidate(), as shown below:
=====================================================
BUG: KMSAN: uninit-value in fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394
d_revalidate fs/namei.c:1030 [inline]
lookup_open fs/namei.c:4405 [inline]
open_last_lookups fs/namei.c:4583 [inline]
path_openat+0x1614/0x64c0 fs/namei.c:4827
do_file_open+0x2aa/0x680 fs/namei.c:4859
[...]
Uninit was created at:
slab_post_alloc_hook mm/slub.c:4466 [inline]
slab_alloc_node mm/slub.c:4788 [inline]
kmem_cache_alloc_lru_noprof+0x382/0x1280 mm/slub.c:4807
__d_alloc+0x55/0xa00 fs/dcache.c:1740
d_alloc_parallel+0x99/0x2740 fs/dcache.c:2604
lookup_open fs/namei.c:4398 [inline]
open_last_lookups fs/namei.c:4583 [inline]
path_openat+0x135f/0x64c0 fs/namei.c:4827
do_file_open+0x2aa/0x680 fs/namei.c:4859
[...]
=====================================================
Reported-by: [email protected]
Closes: https://lore.kernel.org/all/[email protected]
Fixes: 2396356 ("fuse: add more control over cache invalidation behaviour")
Signed-off-by: Luis Henriques <[email protected]>
Signed-off-by: Miklos Szeredi <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
Changed files:
fs/fuse/dir.c
fs/namei.c
mm/slub.c
fs/dcache.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=da3d241c5b925f17a9d8051d7a9e0d454d8e01f6
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-53311 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53311
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:L/UI:N/S:U/C:N/I:L/A:N
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L
The Best / paranoid CVSS score: 4.4
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: unknown
Paranoid ActionableScore: 2
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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