CVE-2026-97564

smb: client: reject userspace cifs.idmap descriptions

Published Sep 25, 2026 CVSS 3.1 · 7.0 High EPSS < 1% KEV · Not listed
Description
In the Linux kernel, the following vulnerability has been resolved:

smb: client: reject userspace cifs.idmap descriptions

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 3da1fdf4efbc ("smb: client: reject userspace
cifs.spnego descriptions"), which applied the same restriction to
cifs.spnego.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4817-1 linux-6.12 security update
Debian DLA Debian DLA DLA-4841-1 linux security update
Debian DSA Debian DSA DSA-6528-1 linux security update
Ubuntu USN Ubuntu USN USN-9019-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-9020-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9022-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9023-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9024-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9025-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9026-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-9039-1 Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN Ubuntu USN USN-9040-1 Linux kernel (Low Latency NVIDIA) vulnerabilities
Ubuntu USN Ubuntu USN USN-9066-1 Linux kernel (HWE) vulnerabilities
Ubuntu USN Ubuntu USN USN-9091-1 Linux kernel (NVIDIA Tegra) vulnerabilities
History
Type Values Removed Values Added
Weaknesses CWE-20
CWE-523
Type Values Removed Values Added
Weaknesses CWE-346
References
Metrics threat_severity

None

cvssV3_1

{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}

threat_severity

Moderate

Type Values Removed Values Added
Weaknesses CWE-20
CWE-523
Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: smb: client: reject userspace cifs.idmap descriptions 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 3da1fdf4efbc ("smb: client: reject userspace cifs.spnego descriptions"), which applied the same restriction to cifs.spnego.
Title smb: client: reject userspace cifs.idmap descriptions
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
Oct 30, 2026, 12:37 PM
Reserved
Sep 24, 2026, 4:01 PM
Status
Received
Published
Sep 25, 2026, 11:17 AM
Modified
Oct 30, 2026, 1:21 PM
Severity
Moderate
Public date
Sep 25, 2026, 12:00 AM