CVE-2002-0698 in Exchange
Summary
by MITRE
Buffer overflow in Internet Mail Connector (IMC) for Microsoft Exchange Server 5.5 allows remote attackers to execute arbitrary code via an EHLO request from a system with a long name as obtained through a reverse DNS lookup, which triggers the overflow in IMC s hello response.
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Analysis
by VulDB Data Team • 09/14/2025
The vulnerability described in CVE-2002-0698 represents a critical buffer overflow flaw within Microsoft Exchange Server 5.5's Internet Mail Connector component. This security weakness specifically manifests during the SMTP communication process when the IMC receives an EHLO command from remote mail servers. The vulnerability arises from insufficient input validation in the IMC's handling of the SMTP greeting response, particularly when processing reverse DNS lookups of connecting systems. When a remote system presents an EHLO command with an excessively long hostname, the IMC's internal buffer fails to properly handle the data length, resulting in memory corruption that can be exploited by malicious actors.
The technical implementation of this vulnerability leverages the standard SMTP protocol's EHLO command which is used to initiate communication between mail servers. During normal operation, when a remote mail server connects to the Exchange IMC, the system performs a reverse DNS lookup to resolve the connecting server's hostname. The IMC then incorporates this hostname into its SMTP greeting response, specifically within the hello response message. When the hostname exceeds the predetermined buffer size allocated for this operation, the excess data overflows into adjacent memory regions, potentially overwriting critical program execution pointers or control data structures. This buffer overflow condition creates an exploitable condition where attackers can manipulate the program flow to execute arbitrary code with the privileges of the Exchange service account.
The operational impact of this vulnerability extends beyond simple remote code execution, as it provides attackers with a potential pathway to compromise entire email infrastructure. Since the Exchange Server 5.5 IMC operates as a critical component for receiving and processing external email messages, successful exploitation could result in complete system compromise. The vulnerability is particularly concerning because it does not require authentication or specific user interaction, making it a true remote exploit that can be leveraged by attackers on the internet. This characteristic places organizations running vulnerable Exchange Server 5.5 systems at significant risk, as the attack surface is effectively the entire SMTP port 25 exposure of the mail server. The exploitability of this vulnerability aligns with attack patterns documented in the mitre ATT&CK framework under the technique of remote code execution through network services, specifically targeting email server infrastructure.
Organizations should implement multiple layers of mitigation strategies to address this vulnerability effectively. The primary recommendation involves applying the official Microsoft security patch released for this specific vulnerability, which corrects the buffer overflow in the IMC's hostname handling routine. Network segmentation and access control measures should be implemented to restrict direct internet access to the Exchange server's SMTP ports, particularly port 25. Additional protective measures include configuring firewalls to limit the types of SMTP commands accepted from external sources, implementing proper input validation at network boundaries, and monitoring SMTP traffic for anomalous EHLO command patterns. From a compliance perspective, this vulnerability aligns with security standards such as those outlined in the CWE database under CWE-121 for stack-based buffer overflow conditions, and represents a critical risk in enterprise email infrastructure management. The vulnerability also demonstrates the importance of proper boundary checking in network protocol implementations and serves as a historical example of how seemingly minor input validation flaws can result in significant security breaches in mission-critical infrastructure components.