CVE-2016-9071 in Firefox
Summary
by MITRE
Content Security Policy combined with HTTP to HTTPS redirection can be used by malicious server to verify whether a known site is within a user s browser history. This vulnerability affects Firefox < 50.
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Analysis
by VulDB Data Team • 10/04/2022
This vulnerability represents a sophisticated tracking mechanism that exploits the interaction between Content Security Policy enforcement and HTTP to HTTPS redirection behaviors in web browsers. The flaw specifically affects Firefox versions prior to 50, where the combination of these two security mechanisms creates an unintended side channel that malicious actors can leverage to determine website visitation patterns. The vulnerability stems from how browsers handle mixed content scenarios when redirecting from insecure to secure contexts, creating observable differences in behavior that reveal user browsing history. Attackers can construct malicious servers that respond differently based on whether a target website has been visited by the user, effectively creating a history-based tracking system that bypasses traditional privacy protections.
The technical implementation of this vulnerability involves exploiting the Content Security Policy directive that controls which sources of content can be loaded within a page, combined with the browser's automatic redirection behavior when encountering HTTP URLs that should be HTTPS. When a browser encounters a mixed content scenario, it may attempt to redirect HTTP resources to their HTTPS equivalents, but this process can produce observable timing differences or behavioral variations. These variations occur because browsers handle redirections differently when they have cached information about previous visits to certain domains, particularly when Content Security Policy directives are in place. The malicious server can detect these differences through timing analysis or by observing the browser's response behavior during the redirection process, thereby inferring whether the user has visited specific sites within their browser history.
The operational impact of this vulnerability extends beyond simple tracking capabilities to represent a significant privacy regression in browser security. Attackers can leverage this vulnerability to perform user profiling based on browsing history, potentially identifying sensitive information about users' online activities without explicit consent or knowledge. The vulnerability is particularly concerning because it operates at the browser level, where users expect strong privacy protections, and it can be exploited through seemingly benign web interactions. This type of tracking is especially dangerous when combined with other privacy reconnaissance techniques, as it can provide attackers with valuable information about user behavior patterns and preferences. The vulnerability affects not just individual users but also organizations that rely on browser security for protecting sensitive data and maintaining user privacy.
Mitigation strategies for this vulnerability require a multi-layered approach that addresses both the specific behavioral patterns that enable the attack and broader security architecture improvements. Browser vendors should implement stricter handling of mixed content scenarios and ensure that redirection behavior does not create observable differences based on user history. The fix typically involves modifying how browsers process Content Security Policy directives in conjunction with HTTP to HTTPS redirection, ensuring that the process remains consistent regardless of whether the target site has been previously visited. Additionally, users should be advised to keep their browsers updated to versions that include the necessary security patches, while security administrators should monitor for signs of exploitation attempts in their network traffic. This vulnerability highlights the importance of considering side-channel attacks in security design and demonstrates how seemingly unrelated security mechanisms can interact in unexpected ways to create new attack vectors. The issue aligns with CWE-204, which addresses information leaks through side channels, and represents a specific implementation weakness in browser security architecture that requires careful attention to prevent similar vulnerabilities from emerging in other contexts.