CVE-2000-0042 in Mail Server
Summary
by MITRE
Buffer overflow in CSM mail server allows remote attackers to cause a denial of service or execute commands via a long HELO command.
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Analysis
by VulDB Data Team • 10/19/2025
The vulnerability identified as CVE-2000-0042 represents a critical buffer overflow flaw within the CSM mail server implementation that exposes systems to remote exploitation. This vulnerability specifically manifests when the mail server processes an excessively long HELO command during the initial SMTP handshake process, creating a condition where user-supplied input exceeds the allocated buffer space. The flaw stems from inadequate input validation and bounds checking mechanisms within the server's command processing logic, allowing malicious actors to craft specially formatted HELO commands that trigger memory corruption. The Common Weakness Enumeration categorizes this issue under CWE-121, which encompasses stack-based buffer overflow conditions that occur when insufficient bounds checking permits writing beyond allocated memory boundaries. The vulnerability operates at the application layer of the network stack, specifically targeting the Simple Mail Transfer Protocol implementation where the HELO command serves as the initial greeting mechanism between mail servers.
The operational impact of this vulnerability extends beyond simple denial of service to encompass potential remote code execution capabilities, making it particularly dangerous for email infrastructure deployments. When an attacker sends a malformed HELO command containing excessive data, the buffer overflow can overwrite adjacent memory locations including return addresses, function pointers, or other critical control data structures. This memory corruption can result in unpredictable program behavior, system crashes, or potentially allow attackers to inject and execute arbitrary code with the privileges of the mail server process. The attack vector requires only network connectivity to the affected mail server port, typically port 25 for SMTP services, making it highly accessible to remote threat actors. According to the MITRE ATT&CK framework, this vulnerability maps to the technique T1203 - Exploitation for Client Execution and T1072 - Software Deployment Tools, as it enables attackers to gain persistent access through compromised mail server infrastructure. The vulnerability affects systems where the CSM mail server software is deployed without proper security patches, particularly in enterprise email environments where SMTP services are exposed to external networks.
Mitigation strategies for CVE-2000-0042 require immediate implementation of security patches provided by the vendor or through third-party security updates, as the vulnerability represents an unpatched condition that has existed for over two decades. Organizations should implement network segmentation to restrict direct access to SMTP ports from untrusted networks, utilizing firewalls and access control lists to limit exposure. Input validation measures must be strengthened to enforce maximum length limits on HELO commands and other SMTP protocol parameters, preventing oversized data from reaching vulnerable processing functions. System administrators should consider implementing intrusion detection systems capable of identifying suspicious SMTP traffic patterns that may indicate exploitation attempts. The principle of least privilege should be enforced by running mail server processes with minimal required permissions, reducing potential impact if exploitation occurs. Additionally, regular security assessments and vulnerability scanning should be conducted to identify any remaining instances of vulnerable CSM mail server installations within network infrastructure. Network monitoring solutions should be configured to detect anomalous traffic patterns associated with buffer overflow exploitation attempts, while log analysis should be performed to identify potential exploitation activities. Organizations should also consider implementing SMTP protocol compliance checking mechanisms that validate command syntax and length restrictions to prevent malformed input from reaching vulnerable code paths. The vulnerability highlights the importance of maintaining up-to-date security patches and proper input validation practices in network services, as similar buffer overflow conditions continue to represent prevalent attack vectors in modern cybersecurity environments.