[CVE-2026-90042][MODERATE REGULAR] ceph: properly decrypt filenames in vmalloc() buffers [ Upstream

[CVE-2026-90042][MODERATE REGULAR] ceph: properly decrypt filenames in vmalloc() buffers [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90042
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ceph: properly decrypt filenames in vmalloc() buffers [ Upstream
Commit: 110747ff535e3d98ac17d68dbd056bb6ef000e23
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=110747ff535e3d98ac17d68dbd056bb6ef000e23
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90042
Analysis date: Wed, 16 Sep 2026 11:31:48 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90042 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90042

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 REGULAR
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-2026-90042	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90042 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-20;CWE-703;CWE-755;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A kernel oops can occur in the CephFS encrypted filename decoding path because ceph_fname_to_usr can pass vmalloc backed MDS message buffers to fscrypt and the scatterlist crypto API expects linear mapped buffers. A malicious or compromised Ceph MDS, or an attacker able to tamper with MDS traffic, may trigger this when encrypted filenames are decoded from large or vmalloc backed replies. For the CVSS the PR:N is used because the attacker does not need a local account on the victim if they can influence the remote MDS endpoint or its traffic. The issue is network reachable in CephFS deployments, but practical exposure is usually limited to trusted storage or data center networks rather than the public Internet. Impact is denial of service via kernel oops. No concrete UAF, OOB write, arbitrary write, or information leak primitive is visible from the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	DISK LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	YES	NO	checked

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

ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3. No floor or cap changed the score.
* Raw paranoid score: 3
* Paranoid score: 3. No additional paranoid point is awarded because the stronger CVSS interpretation changes exploitability assumptions but does not establish a stronger primitive.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Positive signals:

* +2 Remote reachable / network-triggerable in the evaluated deployment. CephFS client code processes MDS reply data, and a malicious or compromised MDS or attacker able to tamper with MDS traffic can influence the buffers passed into encrypted filename decoding.
* +1 Reliable kernel crash / strong DoS. The commit explicitly describes oopses caused by passing vmalloc-backed buffers into fscrypt/scatterlist crypto paths that expect linear-mapped buffers.

Negative signals:

* 0 No host-admin penalty. The attacker model does not require host-admin-equivalent privileges on the victim once the victim is using the affected CephFS configuration.
* 0 No rare-subsystem penalty. CephFS with fscrypt and vmalloc-backed large messages is a deployment condition, but the supplied evidence does not justify treating it as rare and unreachable enough for a scoring subtraction.
* 0 No hard-race penalty. This is not a race. The trigger depends on buffer allocation placement and message processing, not a narrow timing window.

Material non-awarded signals:

* Controlled reclaim not demonstrated.
* Real UAF not demonstrated.
* OOB write not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Information disclosure path not demonstrated.
* Confidentiality and integrity impact not awarded.
* Authorization or security-boundary bypass not demonstrated.
* Filesystem metadata corruption not demonstrated.
* Extra availability point not awarded because the oops/kernel crash is already counted once.
* ImportantCandidate not set because the established primitive is crash-only invalid buffer handling, not a concrete lifetime, ownership, or corruption primitive with unresolved exploitation leverage.

3. Reachability analysis

The vulnerable path is reached when CephFS decodes encrypted filenames from MDS-provided message data. The relevant attacker is a malicious or compromised Ceph MDS, or an attacker able to tamper with MDS traffic. The attacker does not need a local account or host-admin privilege on the victim in that model.

Prior victim-side setup is required: the system must be using CephFS, encrypted filename handling must be involved, and the relevant message buffers must come from kvmalloc memory that may fall back to vmalloc. This limits real-world exposure mostly to storage or data-center networks rather than the public Internet. It does not by itself establish a host-admin requirement for the attacker.

No namespace-scoped privilege chain is involved. No special local namespace capability is needed or relevant. No special physical hardware is required. The condition is not a timing race. Repeated attempts may be possible from a malicious MDS by causing suitable directory or filename replies, but repeatability only strengthens the DoS concern and does not establish a stronger corruption primitive.

4. Primitive and severity interpretation

The exact primitive is an invalid buffer-location mismatch: vmalloc-backed Ceph message slices may be passed to fscrypt/scatterlist crypto code that expects buffers in the linear mapping region. The demonstrated consequence is a kernel oops, especially on non-x86 platforms.

This is not an active structured UAF and not fixed stale storage. There is no concrete repeated release/refcount operation. There is no first lifetime operation that frees an object followed by a second mutation through the same dangling reference.

PrimitiveClass is CLASS_C because the demonstrated behavior is crash/DoS from invalid-state handling without an independently useful corruption primitive. The likely operational severity is a network-influenced kernel DoS in affected CephFS deployments. A stronger consequence such as privilege escalation, arbitrary kernel write, or information disclosure is speculative and not supported by the supplied patch context.

ImportantCandidate=NO because no Class A primitive and no strong Class B unresolved exploitation leverage is established. AutoDowngradeAllowed=YES because this is crash-only Class C behavior with no unresolved kernel corruption, lifetime, ownership, or authorization primitive.

5. One-sentence report phrase

A CephFS client can oops while decrypting encrypted filenames because vmalloc backed MDS message buffers may be passed into fscrypt scatterlist crypto code that expects linear mapped memory, allowing a malicious or compromised MDS path to cause denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the issue is network-influenced through Ceph MDS replies and causes a kernel oops, but the patch does not establish UAF, OOB write, arbitrary write, information leak, or privilege escalation.

7. Call-site confidence

Call-site confidence: high

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

Patch: ceph: properly decrypt filenames in vmalloc() buffers [ Upstream
Commit: 110747ff535e3d98ac17d68dbd056bb6ef000e23
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=110747ff535e3d98ac17d68dbd056bb6ef000e23

Changed files:
  fs/ceph/crypto.c
  fs/ceph/mds_client.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=110747ff535e3d98ac17d68dbd056bb6ef000e23

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

The original Linux kernel CVE announcement for CVE-2026-90042 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90042

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:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 7.5

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: unknown
  Paranoid ActionableScore: 3

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).