CVE-2000-0840 in XMail
Summary
by MITRE
Buffer overflow in XMail POP3 server before version 0.59 allows remote attackers to execute arbitrary commands via a long USER command.
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Analysis
by VulDB Data Team • 10/12/2025
The vulnerability described in CVE-2000-0840 represents a critical buffer overflow flaw within the XMail POP3 server software prior to version 0.59. This issue stems from inadequate input validation mechanisms that fail to properly handle excessively long USER command parameters, creating a exploitable condition that can be leveraged by remote attackers to gain unauthorized system access. The buffer overflow occurs when the server processes a USER command containing more data than the allocated buffer space can accommodate, leading to memory corruption that may result in arbitrary code execution.
The technical implementation of this vulnerability aligns with CWE-121, which categorizes buffer overflow conditions that occur when insufficient space is allocated for data, particularly in stack-based buffer overflows. When an attacker sends a malformed USER command with an excessive number of characters, the server's parsing routine fails to enforce proper bounds checking, causing the overflow to overwrite adjacent memory locations including return addresses and control data. This memory corruption directly enables attackers to manipulate the program execution flow and inject malicious code that executes with the privileges of the affected service.
The operational impact of this vulnerability is severe and encompasses multiple attack vectors within the broader ATT&CK framework, specifically mapping to T1203 - Exploitation for Client Execution and T1059 - Command and Scripting Interpreter. Remote attackers can exploit this condition without requiring authentication, making it particularly dangerous in networked environments where POP3 services are exposed to untrusted networks. Successful exploitation allows adversaries to execute arbitrary commands on the target system, potentially leading to complete system compromise, data exfiltration, or establishment of persistent backdoors. The vulnerability affects the core authentication mechanism of the POP3 protocol, undermining the security of email communications and potentially providing attackers with access to sensitive user credentials and email content.
Mitigation strategies for this vulnerability include immediate deployment of patches released by the software vendor, which typically involve implementing proper input validation and bounds checking mechanisms within the USER command processing routine. System administrators should also consider implementing network segmentation and access controls to limit exposure of POP3 services to trusted networks only. Additional protective measures include deploying intrusion detection systems capable of identifying suspicious USER command patterns and configuring firewalls to restrict access to POP3 ports from untrusted sources. The vulnerability serves as a classic example of why proper secure coding practices, including input validation and memory management, are essential in network services. Organizations should conduct regular security assessments to identify similar buffer overflow vulnerabilities in other network applications and ensure comprehensive patch management processes are in place to address such critical security flaws promptly.