CVE-2002-0270 in Web Browser
Summary
by MITRE
Opera, when configured with the "Determine action by MIME type" option disabled, interprets an object as an HTML document even when its MIME Content-Type is text/plain, which could allow remote attackers to execute arbitrary script in documents that the user does not expect, possibly through web applications that use a text/plain type to prevent cross-site scripting attacks.
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Analysis
by VulDB Data Team • 04/12/2019
This vulnerability exists in Opera web browser versions prior to 7.54 where the browser fails to properly validate MIME content types when rendering web documents. The flaw occurs when the "Determine action by MIME type" option is disabled, which removes the browser's built-in MIME type checking mechanism. When a web application serves content with a text/plain MIME type but includes executable JavaScript within an object tag or similar construct, Opera incorrectly treats this content as HTML, bypassing the intended security restrictions. This behavior creates a dangerous condition where attackers can exploit the browser's content interpretation logic to execute malicious scripts in contexts where such execution would normally be prevented by the text/plain content type designation.
The technical implementation of this vulnerability stems from Opera's fallback mechanism for content rendering when MIME type validation is disabled. When the browser encounters an object element or similar construct containing JavaScript within text/plain content, it does not properly isolate the script execution context. This allows the JavaScript to run within the same security domain as the parent document, effectively bypassing the cross-site scripting protection that text/plain content types are designed to provide. The vulnerability represents a classic case of improper input validation and content type handling, which aligns with CWE-1004 weakness category focusing on insecure coding practices related to content type interpretation.
The operational impact of this vulnerability is significant as it allows remote attackers to perform cross-site scripting attacks against users of affected Opera versions. Attackers can craft malicious web pages that appear to serve text/plain content but contain embedded scripts that execute in the user's browser context. This creates a vector for session hijacking, data theft, and other malicious activities that would normally be prevented by proper MIME type handling. The vulnerability is particularly dangerous because it exploits a user-configured security setting that many users might disable for convenience, making it more likely to be exploited in real-world scenarios. The attack requires no special privileges and can be executed through standard web browsing activities, making it a serious threat to user security.
Mitigation strategies for this vulnerability include upgrading to Opera version 7.54 or later where the issue has been resolved through improved MIME type handling and content validation. Users should also avoid disabling the automatic MIME type detection feature in their browser settings, as this creates the conditions necessary for exploitation. Security administrators should implement proper web application security controls including Content Security Policy headers that can help prevent script execution in unexpected contexts. The vulnerability demonstrates the importance of maintaining proper content type validation at multiple layers of the web application stack and aligns with ATT&CK technique T1059.007 for scripting languages and T1203 for exploitation for privilege escalation through web-based attacks. Organizations should also consider implementing web application firewalls that can detect and block suspicious content type combinations that might indicate exploitation attempts.