CVE-2001-1581 in MAILsweeper
Summary
by MITRE
The File Blocker feature in Clearswift MAILsweeper for SMTP 4.2 allows remote attackers to bypass e-mail attachment filtering policies via a modified name in a Content-Type header.
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Analysis
by VulDB Data Team • 06/06/2018
The vulnerability identified as CVE-2001-1581 resides within the Clearswift MAILsweeper for SMTP version 4.2 email security appliance, specifically targeting its File Blocker functionality designed to prevent malicious attachments from entering corporate email systems. This weakness represents a significant bypass mechanism that undermines the intended security posture of email filtering policies. The flaw operates through manipulation of the Content-Type header within email messages, allowing attackers to circumvent attachment filtering controls by simply renaming files with modified extensions that evade detection mechanisms. The vulnerability demonstrates a critical design flaw in how the system validates and processes email content headers, particularly focusing on the parsing and interpretation of file type information.
The technical exploitation of this vulnerability occurs when an attacker crafts an email message with a Content-Type header containing a modified filename that appears legitimate to the filtering system but actually represents a malicious attachment. The File Blocker feature in MAILsweeper relies on specific file extension patterns and content type identification to determine whether attachments should be blocked or allowed. When attackers modify the filename within the Content-Type header to use extensions that are not explicitly blocked or that are not recognized by the system's filtering rules, they can successfully bypass the intended security controls. This represents a classic example of input validation bypass where the system fails to properly sanitize or validate the filename component within email headers, creating an attack vector that leverages the trust placed in header information.
The operational impact of CVE-2001-1581 extends beyond simple bypass of email filtering policies, potentially enabling attackers to deliver malicious payloads through email channels that would otherwise be blocked by security controls. This vulnerability can be particularly dangerous in enterprise environments where email security appliances are deployed to prevent the delivery of malware, phishing attachments, or other malicious content. The ability to circumvent filtering policies through header manipulation means that attackers can potentially deliver harmful attachments such as executable files, scripts, or documents containing malicious code that could compromise systems, steal credentials, or establish persistence within the network. This vulnerability directly impacts the confidentiality, integrity, and availability of email communications within protected environments, as it allows malicious actors to exploit the trust model inherent in email security systems.
Organizations implementing Clearswift MAILsweeper for SMTP 4.2 should consider immediate remediation through vendor-provided patches or updates that address the header parsing and validation mechanisms. The vulnerability aligns with CWE-20, which describes improper input validation, and represents a failure in the security controls that should prevent unauthorized access to email systems. From an ATT&CK framework perspective, this vulnerability maps to techniques involving command and control communications and initial access through social engineering, as attackers can exploit this weakness to deliver malicious payloads. The mitigation strategy should include not only applying vendor patches but also implementing additional email security measures such as multi-layered content filtering, enhanced header validation, and monitoring for suspicious header modifications that could indicate exploitation attempts. Organizations should also consider implementing network-based intrusion detection systems to monitor for patterns consistent with this specific attack vector and ensure that email security policies are regularly reviewed and updated to address emerging threats.