CVE-2000-0543 in Certificate Server
Summary
by MITRE
The command port for PGP Certificate Server 2.5.0 and 2.5.1 allows remote attackers to cause a denial of service if their hostname does not have a reverse DNS entry and they connect to port 4000.
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Analysis
by VulDB Data Team • 05/11/2019
The vulnerability identified as CVE-2000-0543 represents a significant denial of service weakness in PGP Certificate Server versions 2.5.0 and 2.5.1 that operates through the command port interface. This flaw specifically targets the server's handling of incoming connections on port 4000, which serves as the primary command interface for administrative operations and certificate management functions within the PGP Certificate Server environment. The vulnerability exploits a fundamental design oversight in the server's connection processing logic that fails to properly handle cases where remote hosts lack proper reverse DNS resolution capabilities.
The technical mechanism behind this vulnerability stems from the server's inadequate error handling when processing connection requests from hosts without reverse DNS entries. When a remote attacker establishes a connection to port 4000, the PGP Certificate Server attempts to perform reverse DNS resolution as part of its connection validation process. However, when the hostname cannot be resolved through reverse DNS lookup, the server's processing logic becomes unstable and enters a state that leads to complete service disruption. This behavior creates a predictable denial of service condition that remote attackers can reliably exploit without requiring authentication or specialized privileges.
The operational impact of this vulnerability extends beyond simple service interruption to encompass broader security implications for organizations relying on PGP Certificate Server infrastructure. The vulnerability affects the availability of critical certificate management services, potentially disrupting secure communications, digital signature validation, and certificate issuance processes that depend on the server's functionality. Attackers can leverage this weakness to systematically deny service to legitimate users and administrators who require access to the certificate server for their operational activities. The vulnerability's exploitation does not require any privileged access or complex attack vectors, making it particularly dangerous as it can be executed by any remote party with network connectivity to the affected port.
This vulnerability aligns with CWE-20, "Improper Input Validation," and demonstrates poor error handling practices that violate fundamental security principles for network service implementations. The flaw represents a classic example of how insufficient input validation can lead to service disruption, a pattern commonly referenced in the ATT&CK framework under the "Denial of Service" tactic. Organizations using affected versions of PGP Certificate Server face significant risk of operational disruption, particularly in environments where certificate services are critical for secure communications. The vulnerability also highlights the importance of robust error handling in network services and the potential consequences of relying on external DNS resolution mechanisms without proper fallback or error recovery procedures. Mitigation strategies should include immediate patching of affected systems, implementation of network-level access controls to restrict connections to port 4000, and configuration adjustments to prevent the problematic reverse DNS lookup behavior. The vulnerability underscores the critical need for thorough security testing of network services, particularly regarding error handling and input validation mechanisms that could be exploited to cause service disruption.