CVE-2001-0280 in SLMail Server
Summary
by MITRE
Buffer overflow in MERCUR SMTP server 3.30 allows remote attackers to execute arbitrary commands via a long EXPN command.
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Analysis
by VulDB Data Team • 10/07/2025
The vulnerability identified as CVE-2001-0280 represents a critical buffer overflow flaw within the MERCUR SMTP server version 3.30 that exposes systems to remote code execution attacks. This issue specifically manifests when the server processes the EXPN command, which is used to expand mailing list names and aliases within the Simple Mail Transfer Protocol framework. The buffer overflow occurs because the server fails to properly validate the length of input data provided in the EXPN command, allowing attackers to overflow the allocated memory buffer and potentially overwrite adjacent memory locations.
From a technical perspective, this vulnerability operates through a classic stack-based buffer overflow mechanism where malicious input exceeds the predetermined buffer size allocated for processing the EXPN command. The flaw stems from inadequate input validation and bounds checking within the server's command processing routine, creating an exploitable condition that can be leveraged by remote attackers to inject and execute arbitrary code on the affected system. The vulnerability is particularly dangerous because it allows execution of commands with the privileges of the SMTP service account, which typically runs with elevated system permissions.
The operational impact of this vulnerability extends beyond simple remote code execution to encompass complete system compromise and potential lateral movement within network environments. Attackers exploiting this flaw can gain unauthorized access to mail servers, potentially using them as launching points for further attacks against internal network resources. The vulnerability affects organizations relying on MERCUR SMTP server 3.30 implementations, particularly those with internet-facing mail services that accept EXPN commands from external sources. The attack vector requires no authentication and can be executed remotely, making it highly attractive to automated exploitation tools and malicious actors seeking to compromise email infrastructure.
Security practitioners should recognize this vulnerability as aligning with CWE-121, which describes stack-based buffer overflow conditions, and the broader category of CWE-787, representing out-of-bounds write vulnerabilities. The attack pattern corresponds to techniques documented in the MITRE ATT&CK framework under the T1059.007 sub-technique for command and scripting interpreter, specifically targeting remote command execution capabilities. Organizations should implement immediate mitigations including patching the MERCUR SMTP server to a version that addresses the buffer overflow, disabling the EXPN command if not required, and implementing network segmentation to limit exposure. Additionally, monitoring for unusual EXPN command usage and implementing intrusion detection systems can help identify potential exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation and memory management in network services, particularly those handling untrusted data from external sources, and underscores the necessity of regular security assessments and timely patch management programs.