CVE-2002-1511 in Tightvnc
Summary
by MITRE
The vncserver wrapper for vnc before 3.3.3r2-21 uses the rand() function instead of srand(), which causes vncserver to generate weak cookies.
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Analysis
by VulDB Data Team • 07/19/2019
The vulnerability identified as CVE-2002-1511 affects the VNC (Virtual Network Computing) server implementation prior to version 3.3.3r2-21, specifically within the vncserver wrapper component. This weakness stems from a fundamental cryptographic flaw in how random number generation is handled during the initialization of VNC server sessions. The issue represents a significant security risk as it directly impacts the generation of authentication cookies used by the VNC protocol to secure remote desktop connections. The vulnerability allows attackers to predict or reproduce the random values used in the authentication process, thereby compromising the security of VNC sessions.
The technical flaw manifests in the improper use of random number generation functions within the VNC server wrapper. Instead of properly seeding the random number generator with srand(), the implementation relies on the rand() function alone, which produces predictable sequences when not properly initialized. This flaw directly violates established cryptographic best practices and represents a CWE-330 weakness related to the use of weak random number generators. The rand() function without proper seeding typically produces sequences that repeat after a limited number of calls, making it trivial for attackers to enumerate possible cookie values and gain unauthorized access to VNC sessions. This weakness falls under the broader category of insufficient entropy in cryptographic operations as defined in various security standards.
The operational impact of this vulnerability extends beyond simple authentication bypass, as it creates persistent security risks for any system running vulnerable VNC server versions. Attackers can exploit this weakness to perform session hijacking, unauthorized remote access, and potential privilege escalation within the compromised systems. The vulnerability is particularly dangerous in enterprise environments where VNC servers are commonly used for remote administration, as it allows attackers to gain access to internal systems without requiring additional credentials or exploiting other vulnerabilities. This weakness enables adversaries to maintain persistent access to target systems, making it a high-value target for attackers following the MITRE ATT&CK framework's privileged access techniques.
Mitigation strategies for CVE-2002-1511 primarily involve upgrading to the patched version of VNC server (3.3.3r2-21 or later) where the proper seeding of random number generators has been implemented. System administrators should also consider implementing additional security controls such as network segmentation, firewall rules limiting VNC access to trusted networks, and the use of stronger authentication mechanisms like SSH tunneling for VNC connections. Organizations should conduct vulnerability assessments to identify all systems running vulnerable VNC versions and ensure proper patch management processes are in place. The remediation process should include thorough testing of patched versions to ensure compatibility with existing VNC deployments while maintaining the security improvements necessary to prevent predictable random number generation in authentication cookies.