CVE-2010-0643 in Chrome
Summary
by MITRE
Google Chrome before 4.0.249.89 attempts to make direct connections to web sites when all configured proxy servers are unavailable, which allows remote HTTP servers to obtain potentially sensitive information about the identity of a client user via standard HTTP logging, as demonstrated by a proxy server that was configured for the purpose of anonymity.
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Analysis
by VulDB Data Team • 04/30/2026
This vulnerability in Google Chrome versions prior to 4.0.249.89 represents a significant privacy and security flaw that undermines the intended proxy configuration behavior. The issue occurs when all configured proxy servers become unavailable during network communication attempts, causing the browser to bypass proxy settings and establish direct connections to target web servers. This deviation from expected proxy behavior creates an unexpected exposure vector that can compromise user anonymity and reveal sensitive client information.
The technical flaw stems from Chrome's connection handling logic failing to properly enforce proxy configuration when proxy servers are unreachable. When a proxy server configured for anonymity purposes becomes unavailable, the browser's fallback mechanism incorrectly attempts direct connections instead of maintaining the intended proxy chain or failing gracefully with appropriate error handling. This behavior violates the fundamental principle of proxy-based anonymity systems where all network traffic should be routed through the designated proxy server to maintain user privacy.
The operational impact of this vulnerability is particularly severe in environments where users rely on proxy servers for anonymity or network filtering purposes. Remote HTTP servers can potentially log and analyze client identification information that would normally be obscured by proxy intermediation. This includes user agent strings, connection headers, and other identifying metadata that can be used to correlate network activity with specific users. The vulnerability essentially defeats the purpose of using proxy servers for privacy protection, exposing users to potential tracking and surveillance.
This vulnerability maps to CWE-284 Access Control Bypass, as it represents an unauthorized access to network resources through improper enforcement of access controls. The issue also aligns with ATT&CK technique T1071.001 Application Layer Protocol HTTP where adversaries can leverage such flaws to extract information from network communications. The flaw demonstrates poor error handling in network stack implementations and highlights the importance of proper fallback mechanisms in proxy configurations.
The security implications extend beyond simple privacy concerns to include potential credential exposure and tracking capabilities for malicious actors. When proxy servers are configured for anonymity, users expect their network traffic to be routed through these intermediaries to obscure their true IP addresses and browsing patterns. The vulnerability creates a situation where sensitive information can leak through direct connections, potentially exposing users to targeted attacks or surveillance. Organizations that deploy proxy-based security measures for network protection may find their defenses compromised when users' browsers bypass these configurations.
Mitigation strategies should focus on updating to Chrome versions that properly handle proxy unavailability by either maintaining the proxy configuration or failing gracefully with appropriate error states. Network administrators should implement monitoring to detect unauthorized direct connections and verify that proxy configurations are properly enforced. Users should be educated about the risks of using browsers with outdated proxy handling capabilities and the importance of maintaining current software versions. The vulnerability underscores the critical need for robust network security practices that account for potential fallback behaviors in proxy configurations.