CVE-2003-1016 in MAILsweeper
Summary
by MITRE
Multiple content security gateway and antivirus products allow remote attackers to bypass content restrictions via MIME messages that use malformed quoting in MIME headers, parameters, and values, including (1) fields that should not be quoted, (2) duplicate quotes, or (3) missing leading or trailing quote characters, 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, specifically targeting their handling of MIME (Multipurpose Internet Mail Extensions) headers and parameters. The flaw resides in the improper parsing of MIME message structures where malicious actors can craft emails with malformed quoting sequences that exploit differences in how various mail clients interpret these constructs. The vulnerability stems from insufficient validation of MIME header syntax, allowing attackers to manipulate message content in ways that bypass security restrictions. When security appliances process these malformed MIME messages, they may incorrectly parse the quoting sequences, leading to misinterpretation of message boundaries and content restrictions.
The technical implementation of this vulnerability involves manipulating three specific categories of malformed quoting that can cause inconsistent interpretation across different systems. First, fields that should not be quoted receive improper quotation marks, which may be interpreted as valid content by some parsers while ignored by others. Second, duplicate quotes create ambiguity in parsing logic, potentially causing the security appliance to misidentify parameter boundaries or content segments. Third, missing leading or trailing quote characters can result in parsers incorrectly interpreting the end of quoted strings, leading to truncated or misparsed content. These parsing inconsistencies create opportunities for attackers to embed malicious content within seemingly legitimate email messages, effectively bypassing content filtering mechanisms designed to prevent such threats.
The operational impact of this vulnerability extends beyond simple content filtering bypass, as it can enable attackers to deliver malicious payloads through email channels that would normally be blocked by security appliances. This weakness allows threat actors to exploit the inconsistent behavior of different mail client parsers, potentially leading to successful delivery of phishing emails, malware attachments, or other malicious content. Security administrators may observe false negatives in their content filtering systems, where malicious messages appear to pass through without proper inspection or blocking. The vulnerability is particularly concerning in enterprise environments where email security appliances serve as primary defenses against inbound threats, as it can undermine the entire security posture by allowing bypass of content restrictions that should prevent access to harmful content.
Mitigation strategies for this vulnerability should focus on implementing robust MIME parsing validation that enforces strict adherence to RFC specifications for MIME header syntax. Security products should normalize all MIME header content before processing, ensuring that quoting sequences follow established standards and that malformed constructs are either rejected or properly sanitized. Organizations should update their security appliances to versions that address this specific parsing inconsistency and implement additional layers of email validation beyond simple MIME structure checks. Network security teams should monitor for unusual email patterns that might indicate exploitation attempts and establish logging mechanisms that track MIME parsing anomalies. This vulnerability aligns with CWE-1699 which addresses improper handling of input data and relates to ATT&CK technique T1192 which covers Spearphishing Attachments, as the bypass can enable delivery of malicious attachments through email channels. The remediation process should include comprehensive testing of MIME parsing logic against various malformed quoting scenarios to ensure that security appliances correctly handle edge cases in message processing.