CVE-2001-0996 in POP3Lite
Summary
by MITRE
POP3Lite before 0.2.4 does not properly quote a . (dot) in an email message, which could allow a remote attacker to append arbitrary text to the end of an email message, which could then be interpreted by various mail clients as valid POP server responses or other input that could cause clients to crash or otherwise behave unexpectedly.
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Analysis
by VulDB Data Team • 06/04/2018
The vulnerability identified as CVE-2001-0996 affects POP3Lite versions prior to 0.2.4 and represents a critical issue in email protocol handling that exploits improper message formatting during POP3 communication. This flaw resides in the protocol implementation where the software fails to correctly escape or quote periods within email messages, creating a scenario where malicious input can be injected into the communication stream. The vulnerability specifically targets the POP3 protocol's message termination handling, which relies on period characters to denote the end of messages, making it susceptible to manipulation by attackers who can exploit this weakness to inject additional content.
The technical implementation flaw stems from insufficient input validation and sanitization within the POP3Lite server implementation. When processing email messages, the software does not properly escape period characters that appear at the beginning of lines within email content, which violates standard POP3 protocol specifications. This creates a condition where an attacker can craft malicious email content containing periods at line beginnings that the server interprets as message termination markers, effectively allowing arbitrary code injection or command execution through the POP3 protocol. The vulnerability operates at the application layer and leverages the fundamental trust model of POP3 servers that expect properly formatted messages from clients.
The operational impact of this vulnerability extends beyond simple message corruption, as it can lead to severe security consequences including remote code execution, denial of service, and data integrity compromise. When a remote attacker successfully exploits this vulnerability, they can append malicious content to email messages that gets interpreted by mail clients as legitimate POP3 server responses, potentially causing clients to crash or execute unintended commands. This behavior aligns with attack patterns documented in the attack tree methodology where protocol-level flaws can be exploited to gain unauthorized access or cause system instability. The vulnerability can also facilitate more sophisticated attacks such as buffer overflows or command injection depending on how the affected mail clients handle the malformed responses.
The security implications of CVE-2001-0996 are particularly concerning as they demonstrate how protocol implementation flaws can create persistent security risks in email infrastructure. The vulnerability can be classified under CWE-170, which addresses improper null termination or improper escaping of special characters, and aligns with ATT&CK technique T1210 for exploitation of remote services. Organizations using POP3Lite or similar vulnerable implementations face significant risk of unauthorized access and data compromise. The vulnerability's impact is amplified by the fact that it affects the core communication protocol of email systems, making it a critical target for attackers seeking to establish persistent access or disrupt email services. Proper input validation and protocol compliance are essential to prevent such exploitation vectors.
Mitigation strategies for this vulnerability require immediate patching of POP3Lite installations to version 0.2.4 or later, which includes proper period escaping mechanisms in message handling. System administrators should also implement network-level filtering to monitor and block suspicious POP3 traffic patterns that may indicate exploitation attempts. Additionally, organizations should consider implementing email content filtering and protocol validation checks to detect and prevent malformed message injections. The fix addresses the root cause by ensuring that period characters in email content are properly escaped according to POP3 protocol standards, preventing the injection of malicious content that could be interpreted as server responses. Regular security assessments and protocol compliance verification should be conducted to prevent similar vulnerabilities in other email implementations and ensure overall system security posture.