CVE-2001-1444 in Kerberos
Summary
by MITRE
The Kerberos Telnet protocol, as implemented by KTH Kerberos IV and Kerberos V (Heimdal), does not encrypt authentication and encryption options sent from the server, which allows remote attackers to downgrade authentication and encryption mechanisms via a man-in-the-middle attack.
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Analysis
by VulDB Data Team • 11/17/2024
The vulnerability described in CVE-2001-1444 represents a critical security flaw in the Kerberos authentication protocol implementation within both KTH Kerberos IV and Heimdal Kerberos V systems. This weakness specifically targets the Telnet protocol's integration with Kerberos authentication, creating a significant attack surface that enables malicious actors to manipulate the authentication process. The vulnerability stems from the improper handling of authentication and encryption options within the Kerberos protocol implementation, where these critical security parameters are transmitted in plaintext rather than being properly encrypted. This design flaw directly violates fundamental security principles that require all authentication credentials and security parameters to be protected against interception and modification during transmission.
The technical nature of this vulnerability allows attackers to perform man-in-the-middle attacks by intercepting and modifying the Kerberos authentication negotiation process. When a client attempts to establish a Telnet connection through Kerberos authentication, the server's authentication and encryption options are sent without encryption, making them susceptible to modification by attackers who can insert their own security parameters. This downgrade attack capability specifically targets the cryptographic strength of the connection, potentially forcing the system to negotiate weaker encryption algorithms or authentication mechanisms than originally intended. The vulnerability operates at the protocol level, affecting the Kerberos authentication handshake process and undermining the security guarantees that Kerberos is designed to provide. According to CWE classification, this represents a weakness in the protection of security-critical information, specifically CWE-310, which deals with cryptographic weaknesses in authentication mechanisms.
The operational impact of this vulnerability extends beyond simple authentication failures, as it enables attackers to compromise the entire security infrastructure that relies on Kerberos for authentication. Organizations using KTH Kerberos IV or Heimdal Kerberos V implementations for Telnet services become vulnerable to credential theft, session hijacking, and unauthorized access to sensitive systems. The vulnerability is particularly dangerous because it allows attackers to silently downgrade security mechanisms without detection, making it difficult to identify when an attack has occurred. This weakness undermines the trust model that Kerberos establishes, as the authentication process can be manipulated to weaken the security posture of the entire system. The attack vector is particularly effective against networks where traffic interception is feasible, as the plaintext transmission of authentication parameters provides attackers with clear targets for manipulation.
Mitigation strategies for this vulnerability require immediate implementation of cryptographic protection for all authentication parameters within the Kerberos protocol. System administrators should ensure that all Kerberos implementations properly encrypt authentication and encryption options during negotiation, preventing attackers from intercepting and modifying these critical parameters. The recommended approach involves updating to patched versions of KTH Kerberos IV or Heimdal Kerberos V that address this specific vulnerability, as well as implementing additional network security controls such as encrypted tunnels or secure authentication protocols. Organizations should also consider implementing monitoring solutions that can detect anomalous authentication behavior patterns that might indicate a man-in-the-middle attack attempt. From an ATT&CK framework perspective, this vulnerability maps to techniques involving credential access and defense evasion, as attackers can leverage this weakness to gain access to systems while potentially avoiding detection mechanisms that rely on proper authentication integrity. The vulnerability demonstrates the importance of proper cryptographic implementation and the critical need for protecting all security-critical information during protocol negotiation phases.