CVE-2016-6866 in slock
Summary
by MITRE
slock allows attackers to bypass the screen lock via vectors involving an invalid password hash, which triggers a NULL pointer dereference and crash.
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Analysis
by VulDB Data Team • 09/24/2024
The vulnerability identified as CVE-2016-6866 affects slock, a simple screen locker utility commonly used in X Window System environments. This flaw represents a critical security weakness that undermines the fundamental purpose of screen locking mechanisms designed to protect user sessions from unauthorized access. The vulnerability resides in the password validation process where slock fails to properly handle malformed or invalid password hashes, creating a dangerous condition that can be exploited by malicious actors to bypass the screen lock entirely.
The technical implementation of this vulnerability stems from a NULL pointer dereference error that occurs when slock processes an invalid password hash. When an attacker provides a malformed password hash, the application attempts to dereference a null pointer during the authentication validation process, causing the program to crash and terminate unexpectedly. This crash effectively removes the screen lock protection, leaving the user's session exposed and accessible to unauthorized individuals. The vulnerability is particularly concerning because it operates at the authentication layer where the application should be enforcing strict security controls, yet instead creates a condition that undermines those very controls.
From an operational perspective, this vulnerability presents a significant risk to user session security in environments where slock is deployed as the primary screen locking solution. The crash condition can be triggered remotely or locally, making it exploitable through various attack vectors including social engineering, physical access, or network-based attacks. Once the application crashes, the screen lock is effectively bypassed, allowing attackers to access the user's desktop session without proper authentication. This creates a window of opportunity for information theft, privilege escalation, and other malicious activities that can compromise the entire system.
The impact of this vulnerability aligns with CWE-476, which addresses NULL pointer dereference conditions in software implementations. This weakness specifically manifests as a failure to properly validate input parameters during authentication processes, leading to application instability and security bypass. From the ATT&CK framework perspective, this vulnerability maps to privilege escalation and credential access tactics, as attackers can leverage the screen lock bypass to gain unauthorized access to protected sessions. The vulnerability also demonstrates poor input validation practices that are commonly exploited in privilege escalation attacks, making it a significant concern for system administrators and security professionals.
Mitigation strategies for CVE-2016-6866 should prioritize immediate patching of affected slock implementations, as the vulnerability cannot be effectively worked around through configuration changes alone. System administrators should implement monitoring for unexpected slock crashes and establish incident response procedures to address potential exploitation attempts. Additionally, organizations should consider alternative screen locking solutions that have undergone more rigorous security testing and validation. The vulnerability highlights the importance of proper error handling and input validation in security-critical applications, emphasizing that authentication mechanisms must be robust against both legitimate and malicious input conditions. Regular security audits and penetration testing should be conducted to identify similar weaknesses in other authentication and authorization components of the system infrastructure.