CVE-2009-2071 in Chrome
Summary
by MITRE
Google Chrome before 1.0.154.53 displays a cached certificate for a (1) 4xx or (2) 5xx CONNECT response page returned by a proxy server, which allows man-in-the-middle attackers to spoof an arbitrary https site by letting a browser obtain a valid certificate from this site during one request, and then sending the browser a crafted 502 response page upon a subsequent request.
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Analysis
by VulDB Data Team • 09/06/2019
The vulnerability described in CVE-2009-2071 represents a critical security flaw in Google Chrome versions prior to 1.0.154.53 that affects how the browser handles certificate validation during proxy server interactions. This issue specifically targets the browser's handling of HTTP status codes 4xx and 5xx responses, particularly when these responses are generated by proxy servers during secure HTTPS connections. The flaw stems from Chrome's improper certificate caching mechanism that retains certificates from previous connections even when subsequent proxy responses indicate server failures or redirections. This behavior creates a significant attack surface where malicious actors can exploit the certificate caching logic to execute man-in-the-middle attacks against HTTPS sites.
The technical implementation of this vulnerability involves Chrome's certificate validation process failing to properly distinguish between legitimate server responses and crafted malicious responses from proxy servers. When a user makes an HTTPS request through a proxy, the browser initially establishes a valid certificate connection to the target site. However, during subsequent requests, if the proxy server returns a crafted 502 response (Bad Gateway) or other 4xx/5xx status codes, Chrome's flawed certificate handling mechanism may continue to display the cached certificate from the previous successful connection rather than properly warning the user about the potential security compromise. This cached certificate presentation creates a false sense of security for users who believe they are connecting securely to the intended site, while in reality they may be communicating with an attacker-controlled server.
The operational impact of this vulnerability extends beyond simple certificate confusion, as it fundamentally undermines the trust model that HTTPS is designed to provide. Attackers can exploit this weakness by positioning themselves as man-in-the-middle proxies within the network path between the user and target servers. The attack requires the victim to first establish a legitimate connection to an HTTPS site, allowing Chrome to cache the valid certificate, followed by subsequent malicious proxy responses that trigger the certificate display bug. This vulnerability directly relates to CWE-295 which addresses improper certificate validation and can be mapped to ATT&CK technique T1071.004 for application layer protocol tunneling. The attack vector specifically targets the trust relationship between browsers and proxy servers, potentially allowing attackers to impersonate legitimate websites and capture sensitive user data.
Mitigation strategies for this vulnerability focus on both immediate browser updates and network-level protections. Organizations should ensure all Chrome installations are updated to version 1.0.154.53 or later where this certificate caching behavior has been corrected. Network administrators can implement additional monitoring of proxy server responses and consider deploying certificate pinning mechanisms to prevent the exploitation of cached certificate issues. Browser security policies should be reviewed to ensure proper handling of proxy server responses, particularly those containing error status codes that might trigger certificate display inconsistencies. The vulnerability highlights the importance of robust certificate validation and cache management in web browsers, emphasizing that certificate handling must be resilient against various proxy server response patterns to maintain user security and trust in HTTPS communications.