CVE-2026-97564
UnknownSummary
In the Linux kernel SMB client, the cifs.idmap key type lacks a vet_description hook, unlike its sibling cifs.spnego. This allows userspace to create keys of this type via request_key(2)/add_key(2) and supply authority-bearing fields (owner/group SIDs, uid/gid) without CIFS origin. A request_key(2) call with a non-NULL callout then triggers a root usermodehelper upcall that consumes the unvetted description in root context.
Risk Assessment
A local user can supply forged identity-mapping data that is processed with root privileges, potentially leading to privilege escalation or corruption of SID/uid/gid mappings. The vulnerability affects systems with mounted CIFS shares.
Recommendation
Update the Linux kernel to a version containing the fix that only accepts cifs.idmap descriptions while CIFS is using its private root_cred. Restrict the ability for unprivileged users to create keys if not required.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS