CVE-2003-1177 in Mercur Mailserver
Summary
by MITRE
Buffer overflow in the base64 decoder in MERCUR Mailserver 4.2 before SP3a allows remote attackers to cause a denial of service and possibly execute arbitrary code via a long (1) AUTH command to the POP3 server or (2) AUTHENTICATE command to the IMAP server.
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Analysis
by VulDB Data Team • 07/17/2025
The vulnerability identified as CVE-2003-1177 represents a critical buffer overflow flaw within the base64 decoder component of MERCUR Mailserver version 4.2 prior to service pack 3a. This security weakness resides in the mail server's handling of authentication commands through both POP3 and IMAP protocols, creating a significant attack surface for remote adversaries. The vulnerability specifically manifests when the server processes excessively long authentication commands, allowing attackers to manipulate memory structures through improper input validation. The flaw operates at the protocol level where authentication requests are processed, making it particularly dangerous as it can be exploited without requiring prior authentication credentials, thus presenting an elevated risk to email infrastructure security.
The technical implementation of this vulnerability stems from inadequate bounds checking within the base64 decoding routine that processes authentication tokens sent by clients. When an attacker submits an overly long AUTH command to the POP3 server or an AUTHENTICATE command to the IMAP server, the malformed input causes the decoder to write data beyond the allocated buffer boundaries. This classic buffer overflow condition creates opportunities for stack corruption and potential code execution. The vulnerability maps directly to CWE-121, which describes heap-based buffer overflow conditions, and CWE-125, which addresses out-of-bounds read vulnerabilities. The attack vector specifically aligns with ATT&CK technique T1203, which involves exploiting weaknesses in input validation to execute malicious code through service manipulation.
The operational impact of this vulnerability extends beyond simple denial of service conditions to encompass potential system compromise and unauthorized access to email infrastructure. Remote attackers can leverage this flaw to either crash the mail server, resulting in service disruption and potential data loss, or to execute arbitrary code with the privileges of the mail server process. The implications are particularly severe for organizations relying on MERCUR Mailserver for critical email communications, as successful exploitation could lead to complete system compromise, data exfiltration, or use as a foothold for further network infiltration. The vulnerability affects both POP3 and IMAP protocols, increasing the attack surface and making it more challenging to defend against since multiple authentication mechanisms are compromised simultaneously.
Organizations affected by this vulnerability should prioritize immediate remediation through the installation of the available service pack 3a update from the vendor. The mitigation strategy should also include network-level defenses such as implementing firewall rules to restrict access to mail server ports, particularly those serving POP3 and IMAP services. Security monitoring should be enhanced to detect unusual authentication patterns or command lengths that might indicate exploitation attempts. Additionally, network segmentation and access controls should be strengthened to limit exposure of mail servers to untrusted networks. The vulnerability demonstrates the critical importance of maintaining up-to-date security patches and implementing robust input validation mechanisms in server applications, particularly those handling authentication and protocol processing functions. Organizations should also consider implementing intrusion detection systems capable of identifying buffer overflow exploitation attempts and establish incident response procedures specifically addressing authentication service compromises.