CVE-2006-2206 in UltraVNC
Summary
by MITRE
The MS-Logon authentication scheme in UltraVNC (aka Ultr@VNC) 1.0.1 uses weak encryption (XOR) for challenge/response, which allows remote attackers to gain privileges by sniffing and decrypting passwords.
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Analysis
by VulDB Data Team • 02/24/2017
The vulnerability identified as CVE-2006-2206 affects UltraVNC version 1.0.1, specifically targeting its MS-Logon authentication scheme implementation. This weakness represents a fundamental cryptographic flaw in the remote desktop protocol's authentication mechanism, where the software employs XOR encryption for challenge/response authentication. The vulnerability stems from the use of a weak encryption algorithm that provides minimal security protection for transmitted credentials, making it susceptible to various attack vectors.
The technical flaw manifests in the authentication process where UltraVNC 1.0.1 utilizes XOR encryption to protect challenge-response exchanges during MS-Logon authentication. This encryption method is inherently insecure because XOR operations with a known key or repeated patterns can be easily reversed through cryptographic analysis. When attackers intercept network traffic containing these challenge-response exchanges, they can employ simple decryption techniques to recover the original passwords. The vulnerability specifically targets the authentication scheme's lack of proper cryptographic strength, allowing attackers to perform passive network monitoring and active password recovery.
The operational impact of this vulnerability extends beyond simple credential theft to encompass complete system compromise. Remote attackers who successfully intercept and decrypt authentication traffic can gain unauthorized access to systems running vulnerable UltraVNC versions. This privilege escalation capability enables attackers to execute arbitrary commands, access sensitive data, modify system configurations, and potentially establish persistent access points. The vulnerability is particularly dangerous because it requires no special privileges to exploit, making it accessible to anyone with network access to the target system. This weakness directly aligns with CWE-327, which addresses the use of weak or broken cryptographic algorithms, and represents a classic example of insufficient cryptographic strength in authentication protocols.
Mitigation strategies for this vulnerability include immediate software updates to versions that implement stronger authentication mechanisms, typically through the adoption of more robust encryption algorithms such as AES or RSA-based authentication. Network administrators should implement additional security controls including network segmentation, encrypted communication channels, and monitoring for unusual authentication patterns. The vulnerability demonstrates the critical importance of proper cryptographic implementation in remote access solutions, aligning with ATT&CK technique T1075 which covers remote service manipulation. Organizations should also consider implementing multi-factor authentication and regular security audits to detect and remediate similar weaknesses in their remote access infrastructure. The incident highlights the necessity of following security standards such as NIST SP 800-57 for cryptographic key management and the importance of avoiding deprecated encryption methods in authentication protocols.
The vulnerability serves as a historical example of how weak cryptographic implementations in remote desktop software can create severe security risks. It emphasizes the need for security-by-design principles in authentication mechanisms and demonstrates the long-term consequences of using outdated encryption standards. Modern security practices would require the implementation of secure authentication protocols with proper key exchange mechanisms, making this vulnerability a case study in the evolution of remote access security requirements. The weakness in UltraVNC 1.0.1 represents a clear violation of security best practices and underscores the critical importance of maintaining up-to-date security implementations in remote access solutions.