CVE-2008-3259 in OpenSSH
Summary
by MITRE
OpenSSH before 5.1 sets the SO_REUSEADDR socket option when the X11UseLocalhost configuration setting is disabled, which allows local users on some platforms to hijack the X11 forwarding port via a bind to a single IP address, as demonstrated on the HP-UX platform.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 11/29/2024
The vulnerability described in CVE-2008-3259 represents a significant security flaw in OpenSSH versions prior to 5.1 that affects the X11 forwarding functionality. This issue stems from the improper handling of socket options when the X11UseLocalhost configuration parameter is disabled, creating an avenue for local privilege escalation and port hijacking attacks. The vulnerability specifically impacts systems where the SO_REUSEADDR socket option is honored by the underlying operating system, particularly affecting platforms like HP-UX where the behavior manifests in predictable ways.
The technical flaw resides in the socket programming implementation within OpenSSH's X11 forwarding code. When X11UseLocalhost is disabled, the software fails to properly manage the SO_REUSEADDR flag during socket creation for X11 forwarding connections. This socket option allows multiple sockets to bind to the same address and port combination, which normally should be restricted to prevent conflicts. However, in this case, the omission creates a scenario where local users can exploit the bind operation to capture the X11 forwarding port, effectively hijacking the connection between the client and the X11 server. The vulnerability is particularly concerning because it leverages the legitimate X11 forwarding mechanism to create an attack vector that bypasses normal access controls.
The operational impact of this vulnerability extends beyond simple port hijacking to potentially allow local users to intercept and manipulate X11 traffic, which could lead to session hijacking, data interception, and unauthorized access to graphical applications. Attackers can exploit this weakness to monitor or manipulate X11 forwarding sessions, potentially gaining access to sensitive graphical user interfaces and the underlying data they display. The attack is particularly effective on platforms like HP-UX where the kernel behavior with SO_REUSEADDR is such that it permits the binding to single IP addresses, making the exploitation more reliable and predictable. This vulnerability can be particularly dangerous in environments where OpenSSH is used for remote administration and X11 forwarding is enabled, as it provides a method for local users to escalate privileges and access graphical sessions that should be protected.
The mitigation for this vulnerability requires updating OpenSSH to version 5.1 or later, where the proper socket option handling has been implemented to prevent the unintended binding behavior. System administrators should also consider disabling X11 forwarding when it is not required for specific use cases, as this eliminates the attack surface entirely. Additionally, implementing proper access controls and monitoring for unusual socket binding patterns can help detect potential exploitation attempts. This vulnerability aligns with CWE-119 which addresses improper restriction of operations within a defined access control scope, and maps to ATT&CK technique T1068 which covers local privilege escalation through exploitation of system vulnerabilities. Organizations should also implement network segmentation and monitoring to prevent lateral movement if such an attack is successfully executed, as the compromised X11 forwarding session could potentially provide access to additional system resources and information.