CVE-2001-0712 in Internet Explorer
Summary
by MITRE
The rendering engine in Internet Explorer determines the MIME type independently of the type that is specified by the server, which allows remote servers to automatically execute script which is placed in a file whose MIME type does not normally support scripting, such as text (.txt), JPEG (.jpg), etc.
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Analysis
by VulDB Data Team • 04/07/2017
The vulnerability described in CVE-2001-0712 represents a critical browser security flaw in Internet Explorer's handling of MIME type determination during content rendering. This issue stems from the browser's behavior of making independent decisions about MIME type classification rather than strictly adhering to server-specified content type headers. The fundamental flaw occurs when Internet Explorer's rendering engine attempts to interpret file content based on its own heuristic analysis rather than relying on the explicit MIME type information provided by web servers. This deviation from standard HTTP protocol behavior creates a dangerous attack surface where malicious actors can exploit the browser's automatic content detection mechanisms to bypass security restrictions.
The technical exploitation of this vulnerability occurs when remote servers serve content with misleading MIME type headers while actually delivering executable script code within files that typically do not support scripting. For instance, a server might serve a javascript payload with a content-type header indicating text/plain or image/jpeg, but the browser's rendering engine will still attempt to interpret the file content and execute any embedded script regardless of the declared MIME type. This behavior violates the principle of least privilege and content security policies that browsers should enforce, as it allows arbitrary code execution based on file content rather than explicit type declarations. The vulnerability specifically affects how Internet Explorer handles file extensions and content analysis, creating a scenario where the browser's internal MIME type detection overrides server-side type specifications.
Operationally, this vulnerability poses significant risks to users browsing the web, as it enables drive-by download attacks and cross-site scripting exploits without requiring user interaction beyond visiting a malicious website. Attackers can host malicious code in seemingly benign file formats such as text files or image files, knowing that Internet Explorer will execute the embedded scripts regardless of the file extension or declared MIME type. This creates a persistent threat vector that can be exploited across multiple websites and applications, as the vulnerability exists in the core browser rendering engine rather than specific web applications. The impact extends beyond simple script execution to potentially allow full system compromise through the exploitation of additional vulnerabilities that may be triggered by the execution of malicious code.
Security professionals should consider this vulnerability in the context of the CWE-451 weakness category, which deals with "User Interface Security" and specifically addresses issues related to improper handling of content type information. The vulnerability also maps to several ATT&CK techniques including T1059.007 for "Command and Scripting Interpreter: JavaScript' and T1203 for 'Exploitation for Client Execution'. Organizations should implement comprehensive browser security policies that include disabling automatic script execution, implementing content security policies, and ensuring users employ updated browser versions that have addressed this vulnerability. The remediation approach involves both immediate browser updates from Microsoft and organizational policies that restrict automatic content interpretation, as well as network-level controls that can detect and block suspicious MIME type behaviors. This vulnerability highlights the importance of strict adherence to HTTP standards and proper content validation in web browser implementations, as the failure to respect server-specified content types creates a fundamental security breach in the browser's security model.