CVE-2007-4752 in OpenSSH
Summary
by MITRE
ssh in OpenSSH before 4.7 does not properly handle when an untrusted cookie cannot be created and uses a trusted X11 cookie instead, which allows attackers to violate intended policy and gain privileges by causing an X client to be treated as trusted.
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Analysis
by VulDB Data Team • 07/25/2019
The vulnerability described in CVE-2007-4752 affects OpenSSH versions prior to 4.7 and relates to improper handling of X11 forwarding mechanisms within the secure shell protocol. This flaw exists in the X11 cookie management system where the ssh client fails to properly validate or handle cases where an untrusted cookie cannot be created during X11 forwarding operations. The vulnerability stems from a design weakness in how OpenSSH processes X11 authentication cookies when establishing forwarded X11 connections between a client and server.
The technical implementation flaw occurs when ssh attempts to establish X11 forwarding and encounters a situation where it cannot create a proper untrusted cookie for the X client connection. Instead of properly handling this failure condition or rejecting the connection attempt, the system defaults to using a trusted X11 cookie from a different source. This behavior violates the fundamental security principle of least privilege and creates an implicit trust relationship that should not exist between the X client and the X server. The vulnerability is classified under CWE-284, which addresses improper access control in software systems, specifically in the context of X11 forwarding security mechanisms.
From an operational perspective, this vulnerability allows attackers to bypass intended security policies that separate trusted and untrusted X11 connections. When an attacker can force the system to use a trusted cookie instead of an untrusted one, they effectively gain the ability to perform actions that would normally be restricted to trusted applications. This could enable privilege escalation or unauthorized access to graphical applications running on the target system. The attack vector typically involves manipulating the X11 forwarding process during ssh connections to trigger the cookie handling error condition.
The impact of this vulnerability extends beyond simple access control violations and can enable more sophisticated attacks such as X11 server takeover or unauthorized graphical session access. Attackers can exploit this weakness to gain elevated privileges or access sensitive graphical applications that should be restricted to specific users or processes. The vulnerability is particularly concerning in multi-user environments where X11 forwarding is commonly used, as it undermines the security boundaries that separate different user sessions and applications. This flaw aligns with ATT&CK technique T1078 which covers valid accounts and legitimate credentials for lateral movement, as the vulnerability allows attackers to leverage existing X11 trust relationships to gain unauthorized access.
Mitigation strategies for CVE-2007-4752 require immediate patching of OpenSSH installations to version 4.7 or later where the X11 cookie handling has been properly corrected. Organizations should also implement strict X11 forwarding policies, disable X11 forwarding when it is not required for specific use cases, and monitor for unusual X11 connection patterns that might indicate exploitation attempts. Network segmentation and firewall rules should be configured to restrict X11 forwarding capabilities to only trusted networks and systems. Additionally, security monitoring should include detection of X11 cookie creation failures and unauthorized trust relationship establishment within X11 forwarding sessions. System administrators should also consider implementing application-level controls to restrict which users can establish X11 forwarded connections and monitor for anomalous behavior in X11 authentication mechanisms.