CVE-2000-0546 in Kerberos
Summary
by MITRE
Buffer overflow in Kerberos 4 KDC program allows remote attackers to cause a denial of service via the lastrealm variable in the set_tgtkey function.
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Analysis
by VulDB Data Team • 05/26/2018
The vulnerability identified as CVE-2000-0546 represents a critical buffer overflow flaw within the Kerberos 4 Key Distribution Center (KDC) implementation that fundamentally compromises system stability and availability. This issue specifically manifests in the set_tgtkey function where the lastrealm variable handling creates an exploitable condition that remote attackers can leverage to execute denial of service attacks against Kerberos services. The flaw exists in the authentication infrastructure that was widely deployed in enterprise environments during the late 1990s and early 2000s, making it a significant concern for organizations relying on legacy Kerberos 4 implementations. The vulnerability's impact extends beyond simple service disruption as it demonstrates the inherent risks of poorly validated input handling in critical authentication components.
The technical exploitation of this buffer overflow occurs when the KDC processes authentication requests containing malformed lastrealm data that exceeds the allocated buffer space. This condition arises from insufficient bounds checking in the set_tgtkey function where the lastrealm variable is manipulated without proper validation of input length. The flaw falls under CWE-121, which categorizes buffer overflow vulnerabilities that occur when insufficient space is allocated for data or when bounds checking is inadequate. When exploited, the buffer overflow corrupts adjacent memory locations, leading to unpredictable program behavior and ultimately causing the KDC service to crash or become unresponsive. The vulnerability demonstrates how authentication services, which are supposed to be the cornerstone of security infrastructure, can become attack vectors when subjected to improper input validation.
The operational impact of CVE-2000-0546 extends far beyond simple service interruption as it affects the core authentication infrastructure that many enterprise systems depend upon. Organizations utilizing Kerberos 4 services would experience complete disruption of authentication capabilities, effectively locking out legitimate users while attackers maintain the ability to repeatedly exploit the vulnerability. This creates a scenario where the denial of service attack becomes self-sustaining, as the service remains unavailable until manual intervention occurs to restart the KDC process. The vulnerability also exposes potential for more sophisticated attacks that could leverage the instability to execute arbitrary code, though the primary documented impact remains denial of service. From an attacker perspective, this vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks targeting authentication services. The widespread deployment of Kerberos 4 in enterprise environments during this period meant that a single vulnerable KDC could compromise authentication for entire organizational domains.
Mitigation strategies for this vulnerability primarily involve immediate patching of affected Kerberos 4 implementations, though many organizations were reluctant to upgrade due to compatibility concerns with existing applications. The solution requires careful attention to input validation procedures within the KDC codebase, specifically ensuring that the lastrealm variable handling includes proper bounds checking and length validation. System administrators should implement monitoring solutions to detect anomalous authentication requests that might indicate exploitation attempts, while also considering network segmentation to limit the attack surface. Organizations should also transition away from legacy Kerberos 4 implementations toward more modern authentication protocols such as Kerberos 5 or alternative authentication mechanisms that have addressed similar buffer overflow vulnerabilities through improved memory management practices. The vulnerability serves as a historical example of how authentication infrastructure components require rigorous security testing and validation, particularly when handling user-provided data in critical system functions.