CVE-2007-4138 in Samba
Summary
by MITRE
The Winbind nss_info extension (nsswitch/idmap_ad.c) in idmap_ad.so in Samba 3.0.25 through 3.0.25c, when the "winbind nss info" option is set to rfc2307 or sfu, grants all local users the privileges of gid 0 when the (1) RFC2307 or (2) Services for UNIX (SFU) primary group attribute is not defined.
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Analysis
by VulDB Data Team • 07/25/2019
The vulnerability described in CVE-2007-4138 represents a critical privilege escalation flaw within the Samba implementation of the Winbind nss_info extension. This issue specifically affects Samba versions 3.0.25 through 3.0.25c and occurs when the winbind nss info configuration option is set to either rfc2307 or sfu modes. The flaw stems from improper handling of primary group attributes in Active Directory integration, creating a security boundary violation that allows local users to gain elevated privileges. The vulnerability is particularly concerning because it operates at the system level where user authentication and authorization are managed, potentially enabling attackers to bypass normal access controls and escalate their privileges to the highest system level.
The technical root cause of this vulnerability lies in the idmap_ad.so module's handling of group membership information when the RFC2307 or Services for UNIX primary group attributes are missing from Active Directory user objects. When these attributes are not defined, the nsswitch/idmap_ad.c extension defaults to granting all local users group identifier 0 privileges, which corresponds to the root or administrator group in Unix-like systems. This default behavior creates a privilege escalation vector where any local user can effectively become a system administrator without proper authentication or authorization. The flaw demonstrates poor input validation and default security configuration practices, as the system fails to properly validate the presence of required attributes before assigning elevated privileges.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential system compromise and data exposure. Local users who exploit this vulnerability can gain root-level access to systems running affected Samba versions, enabling them to modify system files, install malicious software, and access sensitive data without detection. This creates a significant risk for organizations relying on Samba for Windows Active Directory integration, as the vulnerability can be exploited by any user with local access to the system. The impact is particularly severe in environments where Samba serves as the primary authentication mechanism between Unix/Linux systems and Windows domains, as it effectively undermines the entire authentication and authorization framework.
Organizations affected by this vulnerability should immediately implement mitigations including updating to patched Samba versions, disabling the problematic winbind nss info options when not required, and implementing additional access controls and monitoring. The vulnerability aligns with CWE-284, which addresses improper access control, and represents a classic example of insufficient privilege checking in system components. From an ATT&CK perspective, this vulnerability maps to privilege escalation techniques and can be leveraged to establish persistent access to systems. Security teams should also consider implementing network segmentation, monitoring for unauthorized privilege escalation attempts, and conducting regular vulnerability assessments to identify systems running unpatched Samba versions that may be susceptible to this and similar attacks. The vulnerability underscores the importance of proper attribute validation and secure default configurations in authentication systems, particularly when integrating different operating system environments.