CVE-2000-0549 in Kerberos
Summary
by MITRE
Kerberos 4 KDC program does not properly check for null termination of AUTH_MSG_KDC_REQUEST requests, which allows remote attackers to cause a denial of service via a malformed request.
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Analysis
by VulDB Data Team • 05/26/2018
The vulnerability identified as CVE-2000-0549 affects the Kerberos 4 Key Distribution Center (KDC) implementation, specifically targeting the AUTH_MSG_KDC_REQUEST message processing functionality. This weakness resides in the authentication protocol that was widely deployed in enterprise environments during the late 1990s and early 2000s, serving as a foundational component for network authentication systems. The issue stems from inadequate input validation within the KDC program's message parsing logic, where the system fails to properly verify that incoming authentication requests contain properly null-terminated strings before processing them. This fundamental flaw creates a condition where malicious actors can craft specially formatted requests that exploit the lack of proper boundary checking.
The technical exploitation of this vulnerability occurs through the manipulation of the AUTH_MSG_KDC_REQUEST message format, where attackers send malformed requests containing non-null-terminated strings to the KDC service. When the KDC attempts to process these requests without proper null termination validation, the parsing routine encounters undefined behavior that leads to memory corruption or stack overflow conditions. The vulnerability is categorized under CWE-121 as a buffer overflow condition that results from improper handling of string data structures, specifically manifesting as a classic stack-based buffer overflow scenario. This type of flaw allows attackers to disrupt the normal operation of the KDC service, which serves as the central authentication authority in Kerberos 4 environments.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a critical weakness in enterprise authentication infrastructure. When successfully exploited, the vulnerability can cause the KDC service to crash or become unresponsive, effectively denying legitimate users access to network resources that depend on Kerberos authentication. This disruption cascades through the entire authentication ecosystem, potentially affecting multiple services and applications that rely on the KDC for user verification. The attack vector is particularly concerning because it requires minimal privileges and can be executed remotely, making it accessible to any attacker with network access to the KDC service. According to ATT&CK framework, this vulnerability maps to T1499.004 (Endpoint Denial of Service) and T1566.002 (Phishing via Service) as attackers can leverage the disruption to create additional attack vectors or simply cause operational chaos.
Mitigation strategies for CVE-2000-0549 involve implementing proper input validation and boundary checking within the KDC implementation, ensuring that all string data is properly null-terminated before processing. Organizations should deploy patches that enforce strict validation of authentication message formats, particularly focusing on string handling routines within the KDC service. Network segmentation and access controls can help limit exposure by restricting direct access to KDC services from untrusted networks. Additionally, implementing intrusion detection systems that monitor for malformed Kerberos 4 requests can provide early warning of exploitation attempts. The most effective long-term solution involves migrating from the deprecated Kerberos 4 protocol to Kerberos 5, which includes enhanced security features and proper input validation mechanisms. System administrators should also implement regular monitoring of KDC service availability and performance metrics to detect potential exploitation attempts. Security hardening of the KDC implementation should include disabling unnecessary services, implementing proper logging and alerting, and ensuring that all authentication requests are subjected to rigorous validation before processing.