CVE-2006-5152 in Internet Explorer
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in Microsoft Internet Explorer allows remote attackers to inject arbitrary web script or HTML via a UTF-7 encoded URL that is returned in a large HTTP 404 error message without an explicit charset, a related issue to CVE-2006-0032.
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Analysis
by VulDB Data Team • 04/23/2026
This cross-site scripting vulnerability exists in Microsoft Internet Explorer due to improper handling of UTF-7 encoded URLs within HTTP 404 error responses. The flaw occurs when a web server returns a large HTTP 404 error message without explicitly declaring the charset, allowing the browser to misinterpret UTF-7 encoded content as UTF-8 or other encodings. When Internet Explorer encounters such malformed responses, it processes the UTF-7 encoded URL fragments as if they were regular HTML content, enabling attackers to inject malicious scripts that execute in the context of the victim's browser session. This vulnerability is categorized under CWE-79 as a failure to sanitize user input, specifically in the context of HTTP response handling and character encoding interpretation.
The technical exploitation of this vulnerability requires an attacker to craft a malicious URL that contains UTF-7 encoded sequences which, when processed by Internet Explorer, are interpreted as HTML markup. The vulnerability is particularly dangerous because it leverages the browser's automatic character set detection mechanisms, bypassing normal security controls. When a user navigates to a crafted URL that triggers a server response containing UTF-7 encoded content, the browser's rendering engine processes these sequences as if they were legitimate HTML, potentially executing embedded JavaScript or other malicious code. This issue represents a variant of the broader class of encoding-based XSS vulnerabilities that have been documented in various browser implementations and is related to CVE-2006-0032 which addressed similar encoding issues in Internet Explorer's handling of character sets.
The operational impact of this vulnerability extends beyond simple script execution, as it allows attackers to perform session hijacking, defacement of web pages, and data theft from authenticated users. An attacker could craft a malicious URL that, when visited by a victim, would display a phishing page or steal session cookies, effectively compromising the user's browser session. The vulnerability affects users who browse the internet using Microsoft Internet Explorer versions that are susceptible to this character encoding interpretation flaw, particularly in environments where users may encounter unexpected 404 error responses from web applications. Security professionals should note that this vulnerability operates at the application layer and can be exploited through social engineering techniques, as users may encounter these malformed URLs while browsing or clicking on links in emails or other web content.
Mitigation strategies for this vulnerability should focus on both server-side and client-side controls. Server administrators should ensure that all HTTP error responses explicitly declare character encodings using the charset parameter in the Content-Type header, preventing browsers from making assumptions about content interpretation. Web applications should sanitize all user-supplied input and properly encode any content that might be displayed in error messages or other responses. Microsoft released patches for this vulnerability through Windows Update, and system administrators should ensure that all Internet Explorer installations are updated with the appropriate security patches. From an operational security perspective, organizations should implement web application firewalls that can detect and block suspicious URL patterns and consider implementing content security policies to prevent script execution in vulnerable contexts. The vulnerability also highlights the importance of proper input validation and output encoding practices in web application development, aligning with defensive techniques outlined in the ATT&CK framework under the T1059.007 sub-technique for scripting and T1566 for social engineering tactics that could leverage such encoding-based vulnerabilities.