* [CVE-2026-93785][LOW] cifs: validate idmap key payload length [ Upstream
@ 2026-09-24 17:48 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-24 17:48 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-93785
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: cifs: validate idmap key payload length [ Upstream
Commit: 6cfeef221ac00d63c07f6122f58e6159bde69ca0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6cfeef221ac00d63c07f6122f58e6159bde69ca0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93785
Analysis date: Thu, 24 Sep 2026 13:48:44 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93785 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93785
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-2026-93785 LOW https://www.kernelcve.org/list/?q=CVE-2026-93785 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:N/I:N/A:H';CWE-197;CWE-681;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'An oversized cifs.idmap key payload can exceed the U16 range of key datalen. The stored length can then be truncated while the full payload is allocated and copied, creating inconsistent bounds for later key consumers. For the CVSS the PR:L reflects that a local process or service must participate in the cifs.idmap key instantiation workflow and have suitable keyring permissions. The issue is not network reachable by itself. No use after free out of bounds access or write primitive is shown by the patch, so confidentiality and integrity impact are not established. Impact is primarily a local availability or reliability issue. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) YES DISK SERVERTOCLIENT DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* No positive primitive score awarded. The patch establishes an integer truncation of `prep->datalen` into the U16-limited `key->datalen`, but does not establish an out-of-bounds read, out-of-bounds write, use-after-free, stale reference, information disclosure, authorization bypass, or crash.
* No remote reachability score awarded. The supplied material does not show that an SMB server or remote peer directly controls `cifs.idmap` key instantiation.
* No local unprivileged trigger score awarded. The supplied patch does not establish that an ordinary user can instantiate or control a `cifs.idmap` key payload through the complete keyring and CIFS idmapping workflow.
* No resource exhaustion score awarded. A payload slightly above `U16_MAX` is rejected before allocation, but the patch does not establish repeatable host-wide memory exhaustion, quota bypass, or persistent leakage.
* No confidentiality or integrity score awarded. Inconsistent stored and allocated lengths alone do not demonstrate a disclosure or modification primitive.
* No privilege escalation or structured semantic reinterpretation score awarded. The later consumers and their behavior are not visible in the supplied context.
* No negative privilege penalty applied. Host-admin-equivalent privilege is not positively established, so `UNKNOWN` is used instead of assuming a restrictive deployment.
3. Reachability analysis
The vulnerable function is a key type instantiate callback for `cifs.idmap` payloads. The supplied patch does not show the full request-key call chain, key permissions, userspace upcall behavior, or whether a remote SMB peer can cause an attacker-selected oversized payload to be installed.
A local component participating in CIFS idmapping may be able to provide the payload, but this does not establish ordinary-user reachability. The complete privilege boundary is unresolved. There is no evidence that the required operation is namespace-scoped or obtainable by an attacker in an unprivileged user or network namespace.
No special hardware, race, boot option, or sysctl prerequisite is indicated. However, the absence of those prerequisites does not establish practical attacker reachability.
4. Primitive and severity interpretation
The exact defect is an integer truncation and inconsistent length invariant: `prep->datalen` can exceed `U16_MAX`, while `key->datalen` cannot represent that value. Before the fix, the full payload could be allocated and copied while the recorded key length was truncated.
This is not a UAF, double release, refcount mutation, active stale-object use, or ownership violation. No active structured-object reuse or fixed stale storage behavior is involved. The patch is validation-only and rejects invalid oversized input with `-EINVAL`.
The patch does not demonstrate what a later key consumer does with the truncated length. Therefore, an invalid-state condition is established, but a meaningful memory-corruption, disclosure, integrity, or privilege-escalation primitive is not. The plausible practical consequence is malformed or unreliable CIFS idmapping behavior, not a demonstrated security boundary failure.
`PrimitiveClass=NONE` is appropriate because the available evidence does not establish a concrete corruption or authorization primitive. `ImportantCandidate=NO` and `AutoDowngradeAllowed=YES` are appropriate because no unresolved Class A or Class B primitive remains.
5. One-sentence report phrase
An oversized cifs.idmap key payload could truncate the U16 key datalen field and create inconsistent payload bounds, but the supplied patch does not establish a concrete memory corruption, disclosure, privilege escalation, or remotely reachable attack primitive.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch is an input-length validation fix, and the supplied evidence does not demonstrate a downstream unsafe consumer, attacker-controlled reachability, or a concrete security consequence beyond inconsistent internal length bookkeeping.
7. Call-site confidence
Call-site confidence: low
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: cifs: validate idmap key payload length [ Upstream
Commit: 6cfeef221ac00d63c07f6122f58e6159bde69ca0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6cfeef221ac00d63c07f6122f58e6159bde69ca0
Changed files:
fs/smb/client/cifsacl.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=6cfeef221ac00d63c07f6122f58e6159bde69ca0
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93785 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93785
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:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
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: unknown
Paranoid ActionableScore: 0
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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