CVE-2009-2057 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer before 8 uses the HTTP Host header to determine the context of a document provided in a (1) 4xx or (2) 5xx CONNECT response from a proxy server, which allows man-in-the-middle attackers to execute arbitrary web script by modifying this CONNECT response, aka an "SSL tampering" attack.
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Analysis
by VulDB Data Team • 08/11/2021
Microsoft Internet Explorer versions prior to 8 contained a critical security flaw in how the browser handled HTTP Host headers within CONNECT responses from proxy servers. This vulnerability specifically affected the browser's interpretation of server responses during SSL/TLS connections, creating an exploitable condition that allowed attackers to manipulate the document context through carefully crafted proxy responses. The flaw emerged from the browser's reliance on the Host header field to establish the security context of content received from proxy servers, particularly when processing 4xx or 5xx status codes during CONNECT operations.
The technical implementation of this vulnerability stemmed from Internet Explorer's failure to properly validate or sanitize the Host header value in proxy responses, creating a path for man-in-the-middle attacks that could execute arbitrary web script code within the browser context. When a proxy server returned a CONNECT response with a modified Host header, the vulnerable browser would incorrectly interpret this information as part of the legitimate connection context, allowing attackers to inject malicious content that would execute with the privileges of the user's browsing session. This represents a classic case of improper input validation and context handling within web browser security architecture, aligning with CWE-20 Improper Input Validation and CWE-119 Improper Restriction of Operations within a Sphere of Influence.
The operational impact of this vulnerability was significant as it enabled attackers to perform SSL tampering attacks without requiring direct access to the encrypted channel, instead exploiting the trust relationship between the browser and proxy server. Attackers could manipulate proxy responses to inject malicious JavaScript or other web content that would execute within the context of the target website, potentially leading to session hijacking, data theft, or further exploitation of the user's browsing session. The vulnerability was particularly dangerous because it leveraged the existing trust model between browsers and proxy servers, making detection difficult and exploitation relatively straightforward for attackers with network access.
This vulnerability aligns with several ATT&CK techniques including T1071.004 Application Layer Protocol: DNS and T1557.001 Adversary-in-the-Middle: ARP Cache Poisoning, though the specific attack vector was more focused on proxy server manipulation rather than traditional man-in-the-middle techniques. The flaw demonstrated a fundamental weakness in how browsers handle proxy responses and highlighted the importance of proper input validation and context establishment in security-critical components. Organizations affected by this vulnerability needed to either upgrade to Internet Explorer 8 or later versions, implement additional proxy security controls, or deploy network-level protections to prevent modification of CONNECT responses. The vulnerability also underscored the need for comprehensive testing of proxy server interactions and proper validation of all HTTP headers received from intermediary servers, as specified in security standards for web application and browser security implementations.
The exploitation of this vulnerability required attackers to have the ability to intercept or modify network traffic between the client and proxy server, making it particularly concerning in environments where network security was insufficient. The impact extended beyond simple script execution to potentially compromise user sessions, steal sensitive data, or provide attackers with persistent access to victim systems. This type of vulnerability demonstrated the complexity of modern web security and the importance of proper security implementation across all layers of the network stack, from proxy servers to end-user browsers.