CVE-2005-4827 in Internet Explorer
Summary
by MITRE
Internet Explorer 6.0, and possibly other versions, allows remote attackers to bypass the same origin security policy and make requests outside of the intended domain by calling open on an XMLHttpRequest object (Microsoft.XMLHTTP) and using tab, newline, and carriage return characters within the first argument (method name), which is supported by some proxy servers that convert tabs to spaces. NOTE: this issue can be leveraged to conduct referer spoofing, HTTP Request Smuggling, and other attacks.
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Analysis
by VulDB Data Team • 05/07/2019
This vulnerability in Internet Explorer 6.0 represents a critical security flaw that undermines the fundamental same origin policy mechanism designed to prevent cross-domain requests. The vulnerability stems from how the browser handles XMLHttpRequest objects when the open method is called with specific character sequences in the method name parameter. Attackers can exploit this weakness by injecting tab, newline, and carriage return characters into the first argument of the XMLHttpRequest open method, which can be processed by certain proxy servers that normalize these characters by converting tabs to spaces. This character manipulation allows malicious actors to bypass the browser's security restrictions that normally prevent scripts from making requests to different domains than the one hosting the script. The vulnerability specifically affects Microsoft.XMLHTTP objects and demonstrates a failure in input validation and sanitization within the browser's scripting engine. This flaw enables attackers to construct requests that appear to originate from different domains, effectively circumventing the browser's origin-based security model that is essential for preventing cross-site scripting attacks and other malicious activities.
The technical exploitation of this vulnerability leverages the way proxy servers handle whitespace characters in HTTP requests, creating a vector that can be used to manipulate the request processing pipeline. When Internet Explorer processes an XMLHttpRequest with malformed method names containing special characters, the browser's handling of these characters can result in requests being interpreted differently than intended by the application code. This creates opportunities for referer spoofing attacks where the browser sends misleading referer headers to web servers, potentially allowing attackers to bypass access controls or perform unauthorized actions. The vulnerability also enables HTTP Request Smuggling techniques where attackers can manipulate the request parsing process to cause servers to process requests incorrectly, potentially leading to session hijacking, data leakage, or other server-side attacks. This type of vulnerability is classified under CWE-284, which deals with improper access control, and represents a failure in proper input validation and sanitization of HTTP method parameters. The weakness in the browser's XMLHttpRequest implementation demonstrates a lack of proper character encoding validation and request normalization that should occur before any network operations are initiated.
The operational impact of this vulnerability extends beyond simple cross-domain requests and creates significant risks for web applications that rely on browser-based security mechanisms. Organizations using Internet Explorer 6.0 in their environments become vulnerable to sophisticated attacks that can bypass authentication mechanisms, access restricted resources, and potentially compromise entire web applications. The vulnerability's ability to enable referer spoofing makes it particularly dangerous for applications that use referer headers for access control decisions or logging purposes. Additionally, the HTTP Request Smuggling capability provides attackers with methods to manipulate server behavior and potentially gain unauthorized access to backend systems. This vulnerability demonstrates how seemingly minor implementation flaws in browser security can create substantial attack vectors that can be leveraged across multiple attack techniques. The impact is particularly severe because the vulnerability affects legacy systems that many organizations continue to use, creating extended attack surfaces that are difficult to remediate without immediate browser upgrades or security patches.
Mitigation strategies for this vulnerability must address both the immediate security concerns and the underlying architectural issues that allow such character manipulation to occur. Organizations should prioritize upgrading to newer versions of Internet Explorer or migrating to modern browsers that properly implement security policies and do not exhibit this character handling behavior. Security patches should be applied immediately if available, though given the age of this vulnerability, such patches may no longer be supported for IE6. Network-level protections can be implemented through proxy server configurations that normalize whitespace characters in HTTP requests before they reach web applications, preventing the character manipulation from being effective. Web application developers should implement additional security controls such as referer validation, request parameter sanitization, and server-side access controls that do not rely solely on browser-based security mechanisms. This vulnerability highlights the importance of implementing defense-in-depth strategies and not relying on browser security features alone for critical access controls. Organizations should also consider implementing web application firewalls that can detect and block suspicious request patterns that may indicate exploitation attempts. The vulnerability serves as a reminder of the critical importance of proper input validation and the need for comprehensive security testing that includes edge cases involving character encoding and whitespace handling in network protocols.