CVE-2000-0550 in Kerberos
Summary
by MITRE
Kerberos 4 KDC program improperly frees memory twice (aka "double-free"), which allows remote attackers to cause a denial of service.
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Analysis
by VulDB Data Team • 05/26/2018
The vulnerability described in CVE-2000-0550 represents a critical memory management flaw within the Kerberos 4 Key Distribution Center (KDC) implementation that fundamentally undermines system stability and availability. This double-free vulnerability occurs when the KDC program attempts to release the same memory block twice during its operation, creating a condition where the memory management system becomes corrupted and potentially exploitable. The issue specifically affects the Kerberos 4 authentication protocol implementation, which was widely deployed in enterprise environments for secure network authentication before being superseded by Kerberos 5. The vulnerability exists at the core of the authentication service where memory allocation and deallocation routines fail to properly track memory usage, leading to undefined behavior when the same memory address is freed multiple times. This flaw represents a classic software bug pattern that has been documented in various security contexts, with the double-free condition being categorized under CWE-415 as an improper handling of memory allocation and deallocation operations. The vulnerability directly impacts the availability of Kerberos 4 services by allowing remote attackers to trigger system instability through carefully crafted authentication requests that exploit this memory management error.
The operational impact of this vulnerability extends beyond simple denial of service to potentially create more serious security implications within affected networks. When the KDC experiences a double-free condition, the system may crash or become unresponsive, effectively preventing legitimate users from authenticating and accessing network resources. This disruption can cascade through enterprise environments where Kerberos 4 was commonly used for single sign-on capabilities across multiple systems and applications. The remote nature of the attack means that adversaries can exploit this vulnerability without requiring local system access, making it particularly dangerous in networked environments. The vulnerability's exploitation typically involves sending specially crafted Kerberos 4 authentication requests that cause the KDC to execute the double-free routine during normal processing. From an adversary perspective, this represents an effective method for conducting denial of service attacks against authentication infrastructure, which can have significant business impact. The attack vector aligns with ATT&CK technique T1499.004 for network denial of service, where attackers target critical infrastructure components to disrupt service availability. The vulnerability affects systems running older versions of Kerberos 4 implementations, particularly those deployed in enterprise environments before the widespread adoption of Kerberos 5, which addressed many of these memory management issues through improved memory handling and validation routines.
Mitigation strategies for CVE-2000-0550 must focus on both immediate remediation and long-term architectural improvements to prevent similar vulnerabilities from occurring in modern authentication systems. The primary solution involves applying vendor-specific patches that correct the memory management implementation within the Kerberos 4 KDC, ensuring that memory allocation and deallocation routines properly track memory usage and prevent duplicate free operations. Organizations should also implement network segmentation and access controls to limit exposure of Kerberos 4 services to untrusted networks, reducing the attack surface for remote exploitation attempts. Monitoring and logging capabilities should be enhanced to detect anomalous authentication patterns that might indicate exploitation attempts, as the double-free condition may manifest as unusual system behavior before complete service disruption. System administrators should consider migrating from Kerberos 4 to Kerberos 5 implementations, which contain improved memory management routines and better protection against such vulnerabilities. Security teams should also implement regular vulnerability assessments and penetration testing to identify similar memory corruption issues in other authentication and network services. The vulnerability serves as a historical example of why proper memory management practices are essential in security-critical software, particularly in authentication systems where reliability and availability are paramount. Organizations should establish robust code review processes that specifically examine memory handling patterns and implement static analysis tools to detect potential double-free conditions and similar memory management errors in software implementations. This vulnerability demonstrates the importance of following secure coding practices and adhering to established security standards such as those outlined in the CERT/CC secure coding guidelines to prevent memory-related vulnerabilities that can compromise system integrity and availability.