A flaw was found in sambas pam_winbind. When mkhomedir is enabled, pam_winbind chowns the target accounts home directory without validating the path is not a critical system directory such as /. On affected systems, accounts with / as their home directory (a common default for system accounts) can have this triggered not only by root, but by a non-root user holding a narrow sudo delegation to run commands as that account, causing ownership of / to change and resulting in severe denial of service (SSH, sudo, and package-manager failures). The change does not grant write access to / (which ships with restrictive 0555 permissions on RHEL), so the impact is availability loss rather than further privilege escalation.
Weakness
The product specifies permissions for a security-critical resource in a way that allows that resource to be read or modified by unintended actors.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Samba | Ubuntu | upstream | * |
Potential Mitigations
- Run the code in a “jail” or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software.
- OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations.
- This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise.
- Be careful to avoid CWE-243 and other weaknesses related to jails.
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/1.html
- https://cwe.mitre.org/data/definitions/122.html
- https://cwe.mitre.org/data/definitions/127.html
- https://cwe.mitre.org/data/definitions/17.html
- https://cwe.mitre.org/data/definitions/180.html
- https://cwe.mitre.org/data/definitions/206.html
- https://cwe.mitre.org/data/definitions/234.html
- https://cwe.mitre.org/data/definitions/60.html
- https://cwe.mitre.org/data/definitions/61.html
- https://cwe.mitre.org/data/definitions/62.html
- https://cwe.mitre.org/data/definitions/642.html
References
- https://access.redhat.com/security/cve/CVE-2026-15779
- https://bugzilla.redhat.com/show_bug.cgi?id=2499991
- https://gitlab.com/samba-team/samba/-/blob/samba-4.19.4/nsswitch/pam_winbind.c
- https://gitlab.com/samba-team/samba/-/blob/samba-4.23.5/nsswitch/pam_winbind.c#L1622
- https://gitlab.com/samba-team/samba/-/blob/samba-4.24.3/nsswitch/pam_winbind.c#L1590