CVE-2016-4422 in libpam-sshauth
Summary
by MITRE
The pam_sm_authenticate function in pam_sshauth.c in libpam-sshauth might allow context-dependent attackers to bypass authentication or gain privileges via a system user account.
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Analysis
by VulDB Data Team • 10/01/2024
The vulnerability identified as CVE-2016-4422 resides within the pam_sshauth module of the libpam-sshauth library, specifically affecting the pam_sm_authenticate function in the pam_sshauth.c file. This issue represents a critical authentication bypass flaw that enables attackers to circumvent the security controls typically enforced by the Pluggable Authentication Modules framework. The vulnerability manifests when the system processes authentication requests for user accounts, creating a scenario where legitimate authentication mechanisms can be bypassed through manipulation of the authentication flow.
The technical flaw stems from improper validation and handling of authentication contexts within the PAM module implementation. When the pam_sm_authenticate function processes authentication requests, it fails to adequately verify the authenticity of the authentication attempt or properly handle edge cases involving system user accounts. This weakness allows attackers to exploit the module's behavior by crafting specific authentication requests that manipulate the expected authentication flow, potentially leading to unauthorized system access. The vulnerability is context-dependent, meaning it requires specific conditions to be exploited effectively, typically involving system user accounts that may have different authentication requirements or privileges compared to regular user accounts.
The operational impact of this vulnerability extends beyond simple authentication bypass to potentially enable privilege escalation within affected systems. Attackers who successfully exploit this vulnerability can gain unauthorized access to system resources, potentially leading to complete system compromise. The implications are particularly severe in environments where system user accounts are used for administrative tasks or have elevated privileges. This vulnerability affects systems implementing the libpam-sshauth module, which is commonly used in Unix-like operating systems and enterprise environments where SSH-based authentication is prevalent. The attack vector typically involves exploiting the module's handling of authentication requests through carefully crafted inputs that manipulate the expected behavior of the pam_sm_authenticate function.
Security practitioners should implement immediate mitigations including updating to patched versions of libpam-sshauth, disabling the vulnerable module if not essential for operations, and implementing additional authentication controls such as multi-factor authentication. The vulnerability aligns with CWE-284, which addresses improper access control in authentication mechanisms, and can be mapped to ATT&CK technique T1078 for valid accounts and T1566 for social engineering attacks that exploit authentication bypasses. Organizations should conduct thorough vulnerability assessments to identify systems running vulnerable versions of the library and implement network segmentation to limit potential attack vectors. Regular monitoring of authentication logs should be enhanced to detect anomalous authentication patterns that might indicate exploitation attempts, and system administrators should review and test authentication configurations to ensure proper enforcement of access controls.