CVE-2006-2194 in ppp
Summary
by MITRE
The winbind plugin in pppd for ppp 2.4.4 and earlier does not check the return code from the setuid function call, which might allow local users to gain privileges by causing setuid to fail, such as exceeding PAM limits for the maximum number of user processes, which prevents the winbind NTLM authentication helper from dropping privileges.
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Analysis
by VulDB Data Team • 06/22/2019
The vulnerability identified as CVE-2006-2194 resides within the winbind plugin implementation of pppd version 2.4.4 and earlier, representing a critical privilege escalation flaw that exploits improper error handling in the setuid function call. This issue specifically affects the winbind NTLM authentication helper component that operates as part of the Point-to-Point Protocol daemon, creating a dangerous condition where local attackers can manipulate the privilege dropping mechanism during authentication processes. The vulnerability stems from the plugin's failure to validate the return status of the setuid system call, which is fundamental to ensuring proper privilege management within Unix-like operating systems.
The technical exploitation of this vulnerability occurs when the winbind plugin encounters circumstances that cause the setuid function to fail, such as when system limits are exceeded for the maximum number of user processes permitted by PAM. When such failures occur, the authentication helper process fails to properly drop its elevated privileges and continues to operate with root-level permissions. This creates a persistent security risk where malicious users can leverage the failed privilege dropping to maintain elevated access to the system. The flaw is particularly insidious because it operates silently during the authentication process, making detection challenging while providing attackers with sustained administrative access.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it fundamentally undermines the security model of the pppd service and its integration with winbind authentication. Attackers can exploit this condition to execute arbitrary code with root privileges, potentially leading to complete system compromise, data exfiltration, or persistent backdoor installation. The vulnerability affects systems that rely on winbind for NTLM authentication within PPP connections, which were commonly used in corporate environments for dial-up and remote access scenarios. This weakness creates a persistent threat vector that remains active as long as the affected pppd service continues to operate with the vulnerable winbind plugin configuration.
Mitigation strategies for CVE-2006-2194 require immediate patching of the pppd software to version 2.4.5 or later, which includes proper error handling for the setuid function calls within the winbind plugin. System administrators should also implement monitoring for failed authentication attempts and privilege escalation events, as well as review and restrict PAM configuration limits to prevent the specific failure conditions that trigger the vulnerability. The fix addresses the underlying CWE-252 weakness related to improper handling of return values from system calls, and aligns with ATT&CK technique T1068 which covers privilege escalation through improper error handling. Organizations should also consider implementing additional security controls such as mandatory access controls, privilege separation mechanisms, and regular security audits of authentication services to prevent similar vulnerabilities from manifesting in other components of their infrastructure.