CVE-2016-2126 in Samba
Summary
by MITRE
Samba version 4.0.0 up to 4.5.2 is vulnerable to privilege elevation due to incorrect handling of the PAC (Privilege Attribute Certificate) checksum. A remote, authenticated, attacker can cause the winbindd process to crash using a legitimate Kerberos ticket. A local service with access to the winbindd privileged pipe can cause winbindd to cache elevated access permissions.
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Analysis
by VulDB Data Team • 10/12/2022
The vulnerability described in CVE-2016-2126 represents a critical privilege escalation flaw within the Samba implementation that affects versions ranging from 4.0.0 through 4.5.2. This issue stems from improper handling of Privilege Attribute Certificates within the Kerberos authentication framework, specifically within the winbindd service component that facilitates integration between Samba and Active Directory environments. The flaw manifests when the system processes Kerberos tickets containing malformed PAC data, creating a condition where the winbindd daemon becomes susceptible to both remote denial of service and local privilege escalation attacks. The vulnerability operates at the intersection of authentication and authorization mechanisms, exploiting weaknesses in how Samba validates and processes security tokens that are essential for maintaining proper access controls in enterprise network environments.
The technical root cause of this vulnerability lies in the incorrect validation of PAC checksums during Kerberos ticket processing within the winbindd service. When a legitimate Kerberos ticket is presented containing specially crafted PAC data, the system fails to properly validate the checksum integrity of the privilege attributes. This validation failure allows an attacker to manipulate the PAC data structure in a way that causes the winbindd process to crash or cache incorrect access permissions. The vulnerability specifically targets the winbindd privileged pipe, which serves as a communication channel between Samba services and the winbind daemon, providing a potential attack vector for local users who can access this privileged interface. According to CWE classification, this represents a weakness in validation of integrity checks, specifically CWE-284 for improper access control and CWE-122 for buffer overflow conditions that can lead to privilege escalation.
The operational impact of CVE-2016-2126 extends beyond simple service disruption to encompass significant security implications for enterprise environments relying on Samba for authentication services. Remote authenticated attackers can leverage this vulnerability to cause denial of service conditions that may disrupt authentication services, while local users with access to the winbindd privileged pipe can potentially escalate their privileges to gain elevated system access. This creates a particularly dangerous scenario where both external and internal threat actors can exploit the vulnerability, making it a high-severity issue for organizations that depend on Samba for Windows domain integration. The vulnerability affects organizations using Samba as a primary authentication mechanism in mixed Windows and Linux environments, where winbindd serves as the bridge between Unix-like systems and Active Directory services, potentially compromising the integrity of the entire authentication infrastructure.
Mitigation strategies for CVE-2016-2126 require immediate patching of affected Samba versions to the latest stable releases that contain the necessary fixes for PAC checksum validation. Organizations should implement network segmentation and access controls to limit exposure of winbindd privileged pipes to only authorized services and users, following principle of least privilege requirements. System administrators should monitor for unusual winbindd process behavior and implement logging controls to detect potential exploitation attempts. The vulnerability aligns with ATT&CK technique T1068 for local privilege escalation and T1566 for credential access through authentication manipulation. Additionally, organizations should consider implementing network-based intrusion detection systems to monitor for suspicious Kerberos ticket structures and PAC data anomalies, as well as conducting regular security assessments of Samba configurations to ensure proper access controls and privilege management are in place. Patch management programs should prioritize this vulnerability due to its potential for both denial of service and privilege escalation impacts within enterprise environments.