CVE-2004-2703 in MIMEsweeper for SMTP
Summary
by MITRE
Clearswift MIMEsweeper 5.0.5, when it has been upgraded from MAILsweeper for SMTP version 4.3 or MAILsweeper Business Suite I or II, allows remote attackers to bypass scanning by including encrypted data in a mail message, which causes the message to be marked as "Clean" instead of "Encrypted".
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Analysis
by VulDB Data Team • 06/07/2017
This vulnerability exists in Clearswift MIMEsweeper version 5.0.5, a security solution designed to scan and filter email messages for malicious content. The flaw specifically affects systems that have been upgraded from older MAILsweeper versions including MAILsweeper for SMTP version 4.3 or MAILsweeper Business Suite I or II. The security mechanism fails to properly identify encrypted content within email messages, creating a significant bypass opportunity for attackers seeking to evade detection.
The technical implementation of this vulnerability stems from the software's inability to correctly process encrypted data within email messages during the scanning process. When encrypted content is included in a message, the system incorrectly categorizes it as "Clean" rather than "Encrypted" as would be expected. This misclassification occurs because the scanning engine fails to properly parse or recognize the encryption indicators that would normally trigger the appropriate security response. The flaw essentially allows malicious actors to embed encrypted payloads within email communications that would otherwise be flagged as suspicious or potentially harmful.
The operational impact of this vulnerability is substantial as it undermines the core security function of the email filtering system. Attackers can exploit this weakness to deliver encrypted malware or malicious payloads that bypass the security controls designed to prevent their execution. This creates a false sense of security for organizations relying on the system, as they believe their email traffic is being properly scanned and filtered. The vulnerability particularly affects organizations that have upgraded from older versions of MAILsweeper, making them susceptible to attacks that could otherwise be prevented by proper encryption detection mechanisms.
This vulnerability aligns with CWE-444, which describes improper handling of input that should be recognized as encrypted or encoded data. The issue also relates to ATT&CK technique T1566, specifically the use of email as an attack vector where adversaries can bypass email filtering systems. Organizations implementing this security solution may find their email security posture significantly weakened, as the system's ability to detect potentially malicious encrypted content becomes compromised. The vulnerability represents a critical gap in the security controls that should be maintaining visibility into all email traffic, particularly concerning the detection of encrypted communications that may contain malicious intent.
The recommended mitigation strategies include immediate patching of the Clearswift MIMEsweeper software to the latest version that addresses this specific vulnerability. Organizations should also implement additional monitoring and logging mechanisms to detect unusual patterns in email traffic that may indicate exploitation attempts. Network administrators should consider implementing additional email security controls beyond the MIMEsweeper solution, such as dedicated encryption detection tools or more advanced email security gateways. Regular security assessments should be conducted to verify that the email filtering system is properly identifying and handling encrypted content. Additionally, security awareness training should be provided to personnel to recognize potential indicators of encrypted malicious content that may bypass automated detection systems.