CVE-2005-4526 in MIMEsweeper For Web
Summary
by MITRE
Clearswift MIMEsweeper For Web (a.k.a. WEBsweeper) 4.0 through 5.1 allows remote attackers to bypass filtering via a URL that does not include a .exe extension but returns an executable file.
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Analysis
by VulDB Data Team • 07/31/2017
The vulnerability identified as CVE-2005-4526 affects Clearswift MIMEsweeper For Web versions 4.0 through 5.1, representing a significant security flaw in email content filtering systems. This issue resides within the web-based email security solution designed to protect organizations from malicious attachments and content. The vulnerability stems from an inadequate file type validation mechanism that relies solely on filename extensions rather than comprehensive content inspection. The affected system operates under the assumption that files with specific extensions like .exe are inherently malicious, while those without such extensions are safe, creating a dangerous false sense of security.
The technical flaw manifests in the application's inability to properly validate file content based on actual file signatures and characteristics rather than merely examining the file extension present in the URL. Attackers can exploit this weakness by crafting URLs that appear benign but actually deliver executable files through alternative extensions or by manipulating server responses to masquerade malicious content as legitimate files. This bypass occurs because the filtering system fails to perform deep content analysis and instead relies on superficial pattern matching based on file extensions. The vulnerability represents a classic example of improper input validation and inadequate security controls, aligning with CWE-20 which addresses "Improper Input Validation" and CWE-502 which deals with "Deserialization of Untrusted Data" when considering the broader context of content handling.
The operational impact of this vulnerability extends beyond simple bypass of security measures, creating substantial risk for organizations relying on MIMEsweeper For Web for email protection. Remote attackers can potentially deliver malware, trojans, or other malicious executables directly to target systems without triggering security alerts, effectively neutralizing the protective measures intended by the email filtering system. This vulnerability undermines the fundamental purpose of content filtering solutions and can lead to unauthorized code execution, data breaches, and system compromise. Organizations using affected versions face increased exposure to phishing attacks, drive-by downloads, and other malicious activities that exploit this specific weakness in the filtering logic.
The exploitation of this vulnerability requires minimal technical skill and can be accomplished through simple URL manipulation techniques, making it particularly dangerous in enterprise environments where users may inadvertently click on malicious links. The attack vector demonstrates a clear path from initial compromise to potential system infiltration, with implications for network security and data protection. Security professionals should consider this vulnerability in relation to ATT&CK technique T1193 which covers "Spearphishing Attachments" and T1059 which addresses "Command and Scripting Interpreter" as attackers can leverage this bypass to execute malicious code on target systems. Organizations should immediately implement mitigations including updating to patched versions of MIMEsweeper For Web, implementing additional content inspection layers, and deploying network-based intrusion detection systems to monitor for suspicious file delivery patterns. The vulnerability also highlights the importance of defense in depth strategies that combine multiple security controls rather than relying on single-point protections, as demonstrated by the failure of extension-based filtering alone to provide adequate protection.