[CVE-2026-97564][MODERATE 7.0] smb: client: reject userspace cifs.idmap descriptions

[CVE-2026-97564][MODERATE 7.0] smb: client: reject userspace cifs.idmap descriptions

[AL-KERNEL]

CVE: CVE-2026-97564
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: smb: client: reject userspace cifs.idmap descriptions
Commit: e5964064e3fbe6325893408faff08ca33de0e2c3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e5964064e3fbe6325893408faff08ca33de0e2c3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97564
Analysis date: Fri, 25 Sep 2026 08:56:47 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97564 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97564

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-2026-97564	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97564 CHECK WITH IMPACT FROM ORIG NN MODERATE	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:H/A:H';CWE-269;*CWE-20;CWE-284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '7.8';DESCR 'A local privilege boundary bypass exists in the CIFS cifs.idmap key type because unprivileged users can create authority bearing key descriptions through add_key or request_key. The description can contain owner and group SID fields and uid gid mapping values that are later consumed by the cifs.idmap request key helper running in root context. For the CVSS the PR:L because a local user process must create and request the key. The issue is not directly network reachable. The direct impact is untrusted identity mapping input reaching a privileged helper. Depending on the installed cifs.idmap helper and request key configuration this may allow a local attacker to obtain elevated privileges or affect data processed with root authority.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	DISK INIT SIMPLEFIX SERVERTOCLIENT LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

No score floor or cap was applied.

2. Signal breakdown

Conservative signals:

* +2 Concrete authorization and security-boundary bypass. The patch adds a mandatory origin check for `cifs.idmap` descriptions. Before the fix, a userspace caller could provide identity authority fields that the root `cifs.idmap` helper treated as kernel-originated.
* +1 Local unprivileged trigger. The supplied context establishes use of `add_key(2)` or `request_key(2)` from userspace. A local process can use its keyring and request the key without host-admin-equivalent privilege.
* +1 Concrete privileged-helper chain. A non-NULL `request_key(2)` callout invokes `/sbin/request-key` and the `cifs.idmap` helper in root context while passing the attacker-controlled key description into that privileged processing path.
* +1 Weak LPE concern. The attacker controls owner/group SID and uid/gid mapping fields that are authority-bearing inputs to a root-context helper. This is more than passive malformed input, but the supplied patch does not establish a complete root-acquisition or arbitrary-command-execution chain.

Paranoid-only adjustment:

* +1 replacing the conservative Weak LPE concern with stronger semantic reinterpretation leverage. The same attacker-controlled identity description crosses a trust boundary and is interpreted by a privileged helper as CIFS kernel-originated authority data. This supports a stronger review priority, but does not prove arbitrary privileged execution.

Important non-awarded signals:

* Controlled kernel-memory reclaim, UAF, OOB access, arbitrary write, and callback control are not demonstrated.
* Confidentiality and integrity consequences such as protected-file access, credential theft, or arbitrary identity replacement are not directly demonstrated by the supplied patch.
* Remote reachability is not established. CIFS networking may be present, but the vulnerable trigger is local keyring and request-key activity.
* A complete local privilege-escalation exploit is not demonstrated. The actual impact depends on the installed `request-key.conf` rules and `cifs.idmap` helper behavior.
* No privilege penalty was applied. The supplied context positively indicates a userspace trigger and does not establish a host-admin prerequisite.

3. Reachability analysis

The evaluated attacker is a local userspace process, not a remote SMB peer. The trigger is creation or lookup of a `cifs.idmap` key using `add_key(2)` or `request_key(2)` with an attacker-controlled description and callout data.

The patch explicitly states that userspace could create this key type before the fix. Normal Linux keyring semantics allow an unprivileged process to create keys in keyrings it controls, subject to ordinary keyring permissions. The vulnerable operation then reaches the root request-key helper path.

No host administrator action is required for the raw key request path once the affected CIFS idmap request-key handler is available. However, the practical privileged consequence depends on deployment-specific components such as `/sbin/request-key`, `request-key.conf`, and the installed `cifs.idmap` helper.

This is not a namespace-scoped networking capability issue. The affected key type and root usermodehelper path are kernel-global security mechanisms, and the supplied evidence does not rely on network namespaces, containers, CAP_NET_ADMIN, or CIFS server access.

No special hardware, boot parameter, race condition, or firmware prerequisite is indicated.

4. Primitive and severity interpretation

The exact primitive is a local confused-deputy and authorization-boundary bypass. A userspace process can supply authority-bearing CIFS identity mapping fields through a key description, while the root `cifs.idmap` helper assumes those fields originated from trusted CIFS kernel code.

This is not a memory-corruption issue. There is no UAF, stale object, double release, refcount mutation, OOB access, or active-object lifetime violation. The defect is instead an incorrect trust-origin decision for security-relevant identity mapping input.

The patch establishes an ALLOW-versus-DENY boundary change. Before the fix, userspace descriptions were accepted and could reach a privileged helper. After the fix, only requests made while CIFS uses its private `root_cred` are accepted. This is sufficient for CLASS_A classification because the patch restores a meaningful kernel-to-userspace authority boundary.

The demonstrated consequence is attacker-controlled identity authority data reaching root-context helper processing. A root privilege escalation, protected-resource theft, arbitrary command execution, or arbitrary uid/gid manipulation is plausible but remains unproven without inspecting the affected request-key configuration and helper parser behavior.

ImportantCandidate is YES because this is a concrete security-boundary bypass involving privileged identity mapping semantics. AutoDowngradeAllowed is NO because automatically treating it as a harmless keyring validation issue could discard an unresolved local privilege-escalation path.

Likely operational severity is Actionable Moderate at minimum. It becomes a Strong Important candidate if the deployed `cifs.idmap` helper can use the supplied uid/gid/SID values to affect privileged authorization, file ownership, key installation, command arguments, or another root-controlled operation.

5. One-sentence report phrase

A local user can inject authority bearing cifs.idmap key descriptions into a root request key helper path, creating a privilege boundary bypass that requires manual review of the deployed cifs.idmap helper and request key configuration.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Inspect the installed `request-key.conf` rule and `cifs.idmap` helper implementation to determine whether attacker-controlled SID, uid, or gid values can cause privileged identity mapping, protected-resource access, unsafe command handling, or local privilege escalation.

7. Call-site confidence

Call-site confidence: medium

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

Patch: smb: client: reject userspace cifs.idmap descriptions
Commit: e5964064e3fbe6325893408faff08ca33de0e2c3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e5964064e3fbe6325893408faff08ca33de0e2c3

Commit description:

cifs.idmap key descriptions carry authority-bearing fields (owner and
group SIDs and uid/gid values in "os:"/"gs:"/"oi:"/"gi:" form) that the
cifs.idmap upcall helper treats as kernel-originating inputs.  Unlike
its sibling cifs.spnego, the cifs.idmap key type has no vet_description
hook, so userspace can create keys of this type through
request_key(2)/add_key(2) and supply those fields without CIFS origin.
A request_key(2) call with a non-NULL callout then drives a root
usermodehelper upcall (/sbin/request-key -> cifs.idmap) that consumes
the unvetted description in root context.

Only accept cifs.idmap descriptions while CIFS is using its private
root_cred to request the key.  id_to_sid()/sid_to_id() already run
under override_creds(root_cred), so the kernel-originated path is
unaffected.

This mirrors commit 3da1fdf ("smb: client: reject userspace
cifs.spnego descriptions"), which applied the same restriction to
cifs.spnego.

Fixes: 4d79dba ("cifs: Add idmap key and related data structures and functions (try #17 repost)")
Reported-by: TencentOS Corvus AI <corvus@tencent.com>
Cc: stable@vger.kernel.org
Assisted-by: CodeBuddy:Kimi-K3
Signed-off-by: Aohan Mei <henrymei@tencent.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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=e5964064e3fbe6325893408faff08ca33de0e2c3

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

The original Linux kernel CVE announcement for CVE-2026-97564 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97564

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:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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).