CVE-2017-11171 in gnome-session
Summary
by MITRE
Bad reference counting in the context of accept_ice_connection() in gsm-xsmp-server.c in old versions of gnome-session up until version 2.29.92 allows a local attacker to establish ICE connections to gnome-session with invalid authentication data (an invalid magic cookie). Each failed authentication attempt will leak a file descriptor in gnome-session. When the maximum number of file descriptors is exhausted in the gnome-session process, it will enter an infinite loop trying to communicate without success, consuming 100% of the CPU. The graphical session associated with the gnome-session process will stop working correctly, because communication with gnome-session is no longer possible.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 12/12/2022
The vulnerability identified as CVE-2017-11171 represents a critical resource management flaw in the gnome-session component of the GNOME desktop environment. This issue specifically affects versions of gnome-session prior to 2.29.92 and stems from improper reference counting mechanisms within the accept_ice_connection() function located in gsm-xsmp-server.c. The flaw creates a pathway for local attackers to exploit the session management system through invalid ICE (Inter-Client Exchange) connections that bypass legitimate authentication mechanisms. The vulnerability operates through a sophisticated attack vector that leverages the underlying X11 session management protocols, where attackers can establish connections using invalid magic cookies that should normally be rejected.
The technical implementation of this vulnerability demonstrates a classic resource leak pattern where each failed authentication attempt results in a file descriptor leak within the gnome-session process. This behavior directly corresponds to CWE-404, which categorizes improper resource management and memory leaks in software systems. The flaw exploits the lack of proper cleanup mechanisms when authentication fails, allowing attackers to repeatedly establish invalid connections without proper resource cleanup. Each connection attempt consumes a file descriptor that remains allocated even after authentication failure, creating a gradual depletion of system resources. The accumulation of these leaked file descriptors eventually exhausts the maximum file descriptor limit imposed on the gnome-session process, leading to system instability.
The operational impact of this vulnerability extends beyond simple resource exhaustion to create a complete system failure scenario that affects the graphical desktop environment. When the maximum file descriptor limit is reached, the gnome-session process enters an infinite loop attempting to communicate while being unable to establish new connections. This condition consumes 100% of available CPU resources, effectively rendering the graphical session unresponsive and non-functional. The attack requires only local privileges, making it particularly dangerous in multi-user environments where an attacker can leverage this vulnerability to disrupt desktop sessions without requiring elevated system access. This behavior aligns with ATT&CK technique T1499.004, which involves resource exhaustion attacks targeting system services.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term architectural improvements to prevent similar issues. The primary solution involves upgrading to gnome-session version 2.29.92 or later, which contains the necessary code fixes that properly implement reference counting and resource cleanup mechanisms. System administrators should also implement monitoring solutions that can detect unusual file descriptor usage patterns and alert on potential exploitation attempts. Additional protective measures include restricting local access to session management services and implementing proper process limits to prevent complete resource exhaustion. The vulnerability highlights the importance of proper resource management in desktop session managers and underscores the need for robust error handling in inter-process communication systems. Organizations should also consider implementing automated patch management processes to ensure timely deployment of security fixes and maintain consistent system security postures against similar exploitation vectors.