CVE-2000-0139 in Internet Anywhere Mail Server
Summary
by MITRE
Internet Anywhere POP3 Mail Server allows local users to cause a denial of service via a malformed RETR command.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 10/19/2025
The vulnerability identified as CVE-2000-0139 affects the Internet Anywhere POP3 Mail Server implementation, representing a significant security flaw that can be exploited to disrupt service availability. This issue specifically targets the Post Office Protocol version 3 implementation used by the Internet Anywhere mail server software, which was widely deployed in enterprise and organizational environments during the late 1990s and early 2000s. The vulnerability resides within the server's handling of client commands, particularly focusing on the RETR command that is fundamental to POP3 protocol operations for retrieving messages from mail servers. This flaw demonstrates a classic buffer overflow or input validation weakness that can be triggered through malformed command sequences.
The technical execution of this vulnerability occurs when a local user crafts a specially malformed RETR command that causes the POP3 server to crash or become unresponsive. The RETR command in POP3 protocol is designed to retrieve specific message numbers from the mail server, and when improperly formatted or when the server fails to properly validate the command parameters, it can lead to memory corruption or unexpected program termination. This type of vulnerability falls under CWE-121, which describes stack-based buffer overflow conditions, and more broadly relates to CWE-122, heap-based buffer overflow conditions, depending on the specific implementation details of the vulnerable server. The attack vector is particularly concerning because it requires only local access to the system, meaning that an attacker with minimal privileges could potentially disrupt mail services for all users on the system.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged to create persistent denial of service conditions that may require manual intervention to resolve. When the POP3 server crashes or becomes unresponsive due to the malformed RETR command, legitimate users cannot access their email accounts through standard POP3 protocols, resulting in communication disruptions that can affect business operations and user productivity. The vulnerability's local nature means that it can be exploited by any user with access to the system, including potentially compromised accounts or insider threats, making it particularly dangerous in multi-user environments where privilege escalation might be possible. This vulnerability aligns with ATT&CK technique T1499.004, which covers the use of network denial of service attacks, though in this case the attack is more specifically categorized as a service disruption rather than a network-level attack.
Mitigation strategies for CVE-2000-0139 should focus on both immediate patching and defensive measures to prevent exploitation. The most effective solution involves applying the vendor-provided security patches that address the input validation flaw in the RETR command handling. Organizations should also implement monitoring systems to detect unusual command patterns or repeated connection attempts that might indicate exploitation attempts. Network segmentation and access controls can limit the potential impact of local exploitation by restricting user access to the mail server system. Additionally, implementing intrusion detection systems that can identify malformed POP3 commands can provide early warning of attempted exploitation. The vulnerability underscores the importance of proper input validation and error handling in server implementations, as highlighted in industry best practices such as those outlined in the OWASP Top Ten and NIST guidelines for secure coding practices. Regular security assessments and vulnerability scanning should be conducted to identify similar issues in other mail server implementations and to ensure that all systems are properly patched against known vulnerabilities.