CVE-2009-2070 in Web Browser
Summary
by MITRE
Opera 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 • 08/11/2021
The vulnerability described in CVE-2009-2070 represents a significant security flaw in Opera web browser's handling of SSL/TLS certificate validation when proxy servers return error responses. This issue specifically affects how Opera manages certificate caching during CONNECT requests, which are essential for establishing secure connections through proxy servers. The flaw manifests when proxy servers return HTTP status codes 4xx or 5xx, particularly the 502 Bad Gateway response, which should normally indicate a proxy error rather than a legitimate secure connection.
The technical mechanism behind this vulnerability involves Opera's certificate caching behavior during proxy communication. When a user makes a request through a proxy server, Opera establishes a CONNECT tunnel to the target server. If the proxy returns a 4xx or 5xx response, Opera incorrectly caches the certificate from the original request rather than properly handling the error condition. This cached certificate can then be reused when the same domain is accessed again, creating a window where attackers can exploit this behavior to perform man-in-the-middle attacks.
The operational impact of this vulnerability is severe as it fundamentally undermines the trust model of SSL/TLS encryption. Attackers can leverage this flaw by first establishing a legitimate connection to a target HTTPS site, allowing Opera to cache the valid certificate. Subsequently, when the user attempts to access the same site, the attacker can intercept the connection and return a crafted 502 response page that Opera will incorrectly validate using the cached certificate. This allows the attacker to present a convincing fake HTTPS site that appears legitimate to the browser, bypassing critical security checks that should prevent such deception.
This vulnerability maps directly to CWE-295 which addresses "Improper Certificate Validation" and aligns with several ATT&CK techniques including T1041 for Exfiltration Over C2 Channel and T1573.1 for Encrypted Channel Communication. The flaw demonstrates how improper handling of proxy error responses can create certificate validation bypass opportunities, representing a critical weakness in the browser's security architecture. The issue particularly affects environments where users rely on proxy servers for web access, making it relevant to corporate networks and organizations that implement proxy infrastructure for traffic monitoring and filtering.
Mitigation strategies for this vulnerability require immediate patching of Opera browser versions to address the certificate caching behavior during proxy error responses. Organizations should ensure all Opera installations are updated to versions that properly handle 4xx and 5xx responses without caching invalid certificates. Network administrators should consider implementing additional monitoring for unusual proxy behavior and certificate validation patterns. Browser security policies should be reviewed to ensure proper handling of proxy errors, and users should be educated about the risks of accessing sensitive sites through untrusted proxy infrastructure. Additionally, organizations may need to implement certificate pinning mechanisms or other advanced security controls to prevent exploitation of this specific vulnerability.