CVE-2008-1545 in Internet Explorer
Summary
by MITRE
The setRequestHeader method of the XMLHttpRequest object in Microsoft Internet Explorer 7 does not restrict the dangerous Transfer-Encoding HTTP request header, which allows remote attackers to conduct HTTP request splitting and HTTP request smuggling attacks via a POST containing a "Transfer-Encoding: chunked" header and a request body with an incorrect chunk size.
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Analysis
by VulDB Data Team • 07/31/2021
The vulnerability described in CVE-2008-1545 represents a critical security flaw in Microsoft Internet Explorer 7's implementation of the XMLHttpRequest object. This issue stems from the improper handling of HTTP headers within the browser's client-side scripting environment, specifically affecting how the setRequestHeader method processes the Transfer-Encoding header. The flaw exists in the browser's HTTP request processing pipeline where it fails to properly validate or sanitize the Transfer-Encoding header, creating an avenue for malicious actors to exploit the underlying HTTP protocol implementation.
The technical implementation of this vulnerability resides in the XMLHttpRequest object's setRequestHeader method which should enforce strict validation of HTTP headers to prevent the injection of potentially dangerous headers. When a malicious attacker constructs a POST request with a Transfer-Encoding: chunked header and deliberately malformed chunk sizes, the vulnerable browser fails to reject or properly process these headers, allowing the malicious content to be transmitted through the HTTP connection. This improper header handling creates a direct pathway for HTTP request splitting attacks where the attacker can manipulate how the server processes the request, potentially leading to various security exploits including cache poisoning, cross-site scripting, and session hijacking. The vulnerability specifically affects the HTTP protocol's chunked transfer encoding mechanism, which is designed to allow data to be transmitted in chunks without requiring the sender to know the total size of the data being sent.
The operational impact of this vulnerability extends beyond simple request manipulation, creating a significant threat vector for man-in-the-middle attacks and server-side exploitation. Attackers can leverage this flaw to perform HTTP request smuggling by crafting requests that appear valid to the client but contain malicious headers that cause the server to process different requests than intended. This vulnerability directly maps to CWE-117, which addresses improper output neutralization for logs, and more specifically to CWE-444, which deals with improper handling of HTTP requests. The attack surface includes any web application that relies on user input processed through XMLHttpRequest objects in Internet Explorer 7, making it particularly dangerous in enterprise environments where legacy browser support is maintained. The vulnerability enables attackers to bypass security controls, potentially leading to unauthorized access to sensitive data, privilege escalation, and the ability to perform actions on behalf of authenticated users.
Mitigation strategies for this vulnerability require immediate remediation through browser updates and security patches, as Microsoft released specific fixes for Internet Explorer 7 to address this header validation issue. Organizations should implement network-level protections such as web application firewalls that can detect and block malformed HTTP requests containing suspicious Transfer-Encoding headers. The implementation of strict header validation policies at the application level can help prevent exploitation by ensuring that only properly formatted headers are accepted from client-side scripts. Security teams should also consider implementing monitoring solutions that can detect unusual patterns in HTTP request processing that might indicate exploitation attempts. According to ATT&CK framework, this vulnerability maps to T1190 for Proxy Execution and T1071.002 for Application Layer Protocol: Web Protocols, highlighting the need for comprehensive network traffic monitoring and application security controls. Organizations should also implement proper input validation and sanitization measures to ensure that any user-supplied data processed through XMLHttpRequest objects is properly validated before being transmitted to backend servers. The vulnerability demonstrates the critical importance of maintaining up-to-date browser security patches and implementing defense-in-depth strategies that protect against both client-side and server-side exploitation vectors.