CVE-2001-1443 in Kerberos
Summary
by MITRE
KTH Kerberos IV and Kerberos V (Heimdal) for Telnet clients do not encrypt connections if the server does not support the requested encryption, which allows remote attackers to read communications via a man-in-the-middle attack.
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Analysis
by VulDB Data Team • 11/17/2024
The vulnerability described in CVE-2001-1443 represents a critical security flaw in KTH Kerberos IV and Heimdal implementations of Telnet client authentication and encryption mechanisms. This issue specifically affects the Kerberos authentication protocols when used in conjunction with Telnet services, creating a scenario where communication security can be easily compromised. The vulnerability stems from the client's failure to properly handle encryption negotiation failures, leading to unencrypted communication channels being established when encryption is not supported by the remote server. This behavior directly violates fundamental security principles of encrypted communication and creates a significant attack surface for malicious actors.
The technical flaw manifests when Kerberos-authenticated Telnet clients attempt to establish secure connections with servers that either do not support encryption or cannot negotiate the required encryption parameters. In such scenarios, the client should either refuse to establish a connection or fall back to a secure alternative, but instead the implementation fails to enforce encryption requirements. This creates a downgrade attack vector where attackers can intercept and read plaintext communications, effectively bypassing the security controls that Kerberos is designed to provide. The vulnerability is particularly dangerous because it operates at the protocol level, affecting the fundamental trust model between client and server components.
From an operational impact perspective, this vulnerability exposes organizations to significant risks including credential theft, session hijacking, and sensitive data interception. Attackers can exploit this weakness through man-in-the-middle attacks, capturing authentication credentials and session data that would normally be protected by encryption. The vulnerability affects systems where Kerberos is used for authentication in Telnet environments, which were common in enterprise networks during the early 2000s. This issue demonstrates the critical importance of proper fallback mechanisms and encryption enforcement in security protocols, as the failure to maintain encryption integrity can completely undermine the security benefits of authentication mechanisms.
The vulnerability aligns with CWE-310, which addresses cryptographic weaknesses in authentication protocols, and maps to ATT&CK technique T1046 for network service scanning that can lead to exploitation of weak encryption. Organizations should implement mandatory encryption requirements for all Kerberos-authenticated connections, ensure proper fallback handling for encryption negotiation failures, and deploy network monitoring to detect unusual communication patterns. System administrators must verify that Telnet clients are configured to reject unencrypted connections when encryption cannot be negotiated, and consider migrating to more secure protocols such as SSH that provide better encryption guarantees and do not suffer from this particular vulnerability. The incident highlights the need for comprehensive protocol security testing and the importance of maintaining strong cryptographic standards even in legacy systems.