CVE-2004-0161 in MAILsweeper
Summary
by MITRE
Multiple content security gateway and antivirus products allow remote attackers to bypass content restrictions via MIME messages that use RFC2231 encoding, which may be interpreted differently by mail clients.
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Analysis
by VulDB Data Team • 06/21/2018
This vulnerability affects content security gateways and antivirus products that process email messages through MIME encoding mechanisms. The flaw resides in how these security appliances handle RFC2231 encoding, a standard for encoding parameter values in mime headers that allows for internationalized character sets and extended character handling. When mail clients encounter MIME messages with RFC2231 encoding, they may interpret the encoded content differently than the security appliances, creating a discrepancy in how the message content is processed and evaluated for security threats.
The technical implementation of this vulnerability stems from inconsistent interpretation of RFC2231 encoded parameters within MIME headers. Security gateways and antivirus systems typically parse MIME messages to identify potential threats, examine file attachments, and enforce content restrictions. However, when RFC2231 encoding is present in message headers, particularly in filename parameters or content disposition headers, the security appliances may not properly decode or interpret these parameters according to the standard. This inconsistency allows attackers to craft malicious email messages where the encoded headers appear benign to the security appliance but are interpreted as containing harmful content by mail clients.
The operational impact of this vulnerability extends beyond simple content restriction bypass, as it enables attackers to circumvent security policies designed to prevent the delivery of malicious attachments or content. Attackers can exploit this weakness by encoding potentially harmful filenames, content types, or other header parameters in such a way that the security appliance fails to recognize the malicious intent while mail clients properly decode and process the content. This creates a window of opportunity where malicious content can pass through security controls undetected, potentially leading to malware delivery, phishing attempts, or other security breaches that would otherwise be prevented by proper content filtering.
The vulnerability aligns with CWE-116, which addresses improper encoding or escaping of output, and relates to ATT&CK technique T1192, which involves exploitation of vulnerabilities in content security systems. Organizations using affected security appliances may experience unauthorized access to systems through email-based attacks, as the bypass allows malicious payloads to reach end users who may not be protected by the security appliance's filtering capabilities. This issue particularly affects enterprise email security systems, web application firewalls, and content inspection appliances that rely on MIME parsing for threat detection.
Mitigation strategies should focus on updating security appliances to versions that properly implement RFC2231 decoding according to standards, implementing additional layers of email inspection beyond simple MIME parsing, and establishing monitoring for unusual MIME header patterns that may indicate exploitation attempts. Security administrators should also consider deploying email authentication mechanisms such as DKIM and DMARC to complement content filtering, as well as implementing network segmentation to limit the potential impact of successful exploitation. Regular security testing and vulnerability assessments should include validation of MIME header processing to ensure that security appliances correctly handle RFC2231 encoded content and maintain their intended protective functions against malicious email content.