CVE-2013-4476 in Samba
Summary
by MITRE
Samba 4.0.x before 4.0.11 and 4.1.x before 4.1.1, when LDAP or HTTP is provided over SSL, uses world-readable permissions for a private key, which allows local users to obtain sensitive information by reading the key file, as demonstrated by access to the local filesystem on an AD domain controller.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 06/02/2021
The vulnerability identified as CVE-2013-4476 represents a critical privilege escalation issue within Samba implementations that affects versions 4.0.x prior to 4.0.11 and 4.1.x prior to 4.1.1. This flaw specifically manifests when Samba is configured to provide LDAP or HTTP services over SSL/TLS encryption protocols. The core technical issue stems from improper file permission handling where the private key file used for SSL termination is created with world-readable permissions, allowing any local user on the system to access the cryptographic material. This vulnerability operates under the principle of least privilege violation, where sensitive security assets are unnecessarily exposed to unauthorized access. The weakness directly maps to CWE-732: Incorrect Permission Assignment for Critical Resource, which categorizes improper access control mechanisms that allow unauthorized users to access protected resources. The vulnerability is particularly dangerous in Active Directory domain controller environments where Samba serves as a critical infrastructure component for authentication and directory services.
The operational impact of this vulnerability extends beyond simple information disclosure, as the private key material can be used by attackers to impersonate legitimate services, decrypt communications, and potentially gain deeper access to the domain controller infrastructure. Local users who exploit this vulnerability can read the private key file and subsequently use it to establish unauthorized connections to services that trust the certificate authority. This creates a pathway for attackers to perform man-in-the-middle attacks against Samba services, potentially compromising the entire domain authentication infrastructure. The attack vector is particularly concerning because it requires no network access or authentication, relying purely on local privilege escalation within the system. According to ATT&CK framework, this vulnerability aligns with T1068: Local Privilege Escalation and T1552: Unsecured Credentials, as it allows unauthorized access to cryptographic keys that are typically protected. The vulnerability also enables potential lateral movement within the domain environment as attackers can use the compromised private key to authenticate to other systems that rely on the same certificate infrastructure.
Mitigation strategies for CVE-2013-4476 require immediate remediation through software updates to patched versions of Samba that properly enforce restricted permissions on private key files. System administrators should ensure that any private key files are created with restrictive permissions such as 600 or 640, preventing world-readable access while maintaining necessary operational functionality. The implementation of proper file system auditing and monitoring can help detect unauthorized access attempts to sensitive cryptographic materials. Organizations should also implement regular security assessments to identify and remediate similar permission misconfigurations across their infrastructure. Additional defensive measures include implementing mandatory access controls, using certificate management systems that automatically enforce proper key permissions, and conducting regular vulnerability scanning to identify unpatched systems. The vulnerability highlights the importance of secure configuration management and proper security hardening practices for critical infrastructure components like domain controllers and authentication services. Organizations should also consider implementing network segmentation and monitoring to detect potential abuse of compromised credentials or cryptographic materials within their environments.