CVE-2001-0154 in Internet Explorer
Summary
by MITRE
HTML e-mail feature in Internet Explorer 5.5 and earlier allows attackers to execute attachments by setting an unusual MIME type for the attachment, which Internet Explorer does not process correctly.
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Analysis
by VulDB Data Team • 06/25/2021
The vulnerability described in CVE-2001-0154 represents a critical security flaw in Internet Explorer 5.5 and earlier versions that exploited the email handling mechanisms within the browser. This issue specifically targeted the HTML email processing functionality where the browser failed to properly validate and handle unusual MIME types associated with email attachments. The flaw allowed malicious actors to craft email messages that appeared legitimate while containing harmful attachments that would execute automatically when users opened the email. This vulnerability was particularly dangerous because it leveraged the trust users placed in their email clients and the automatic execution behavior of older web browsers when processing rich content.
The technical root cause of this vulnerability stems from improper input validation within Internet Explorer's email processing engine. When the browser encountered email attachments with non-standard MIME types, it failed to properly sanitize or reject these unusual content identifiers. This processing error occurred at the MIME type parsing layer where the browser's security boundaries were not properly enforced. The vulnerability was classified under CWE-20 as "Improper Input Validation" and specifically demonstrated how inadequate MIME type handling could lead to arbitrary code execution. Attackers could manipulate the Content-Type header of email attachments to use unusual or crafted MIME types that would bypass the browser's normal security checks, causing the system to treat the attachment as executable content.
The operational impact of this vulnerability was severe and widespread given the prevalence of Internet Explorer 5.5 in corporate and personal environments during the early 2000s. Users who opened malicious emails would experience automatic execution of harmful code without proper user interaction or warning prompts. This automated execution behavior made the vulnerability particularly dangerous for phishing campaigns and social engineering attacks, as victims could be compromised simply by reading their email. The attack vector aligned with ATT&CK technique T1193 "Spearphishing Attachment" and could lead to full system compromise through techniques such as T1059 "Command and Scripting Interpreter" and T1068 "Exploitation for Privilege Escalation". Organizations with significant Internet Explorer usage were particularly vulnerable, as the attack required no sophisticated user interaction beyond opening an email message.
Mitigation strategies for this vulnerability focused on both immediate remediation and long-term security improvements. The most effective immediate solution was updating to Internet Explorer 6.0 or later versions where Microsoft had addressed the MIME type handling issues. System administrators should have implemented email filtering solutions that could detect and block suspicious MIME types, particularly those with unusual or non-standard content identifiers. Additionally, user education regarding email security became crucial, emphasizing the dangers of opening unexpected attachments even from known senders. Security configurations should have included disabling automatic execution of email attachments and implementing strict MIME type validation at email gateway levels. Organizations could also have deployed network-based intrusion detection systems to monitor for patterns associated with this specific vulnerability, and implemented sandboxing techniques to isolate email processing from critical system resources. The vulnerability highlighted the importance of proper input validation and the need for comprehensive security testing of email processing components within web browsers.