CVE-2016-2830 in Firefox
Summary
by MITRE
Mozilla Firefox before 48.0 and Firefox ESR 45.x before 45.3 preserve the network connection used for favicon resource retrieval after the associated browser window is closed, which makes it easier for remote web servers to track users by observing network traffic from multiple IP addresses.
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Analysis
by VulDB Data Team • 10/23/2024
This vulnerability in Mozilla Firefox and Firefox ESR versions prior to 48.0 and 45.3 respectively represents a significant privacy and tracking concern that stems from improper connection management during favicon retrieval operations. The flaw allows remote web servers to observe network traffic patterns from multiple IP addresses, effectively enabling persistent tracking of user activities across different browsing sessions and window closures. This behavior violates fundamental web privacy principles and creates opportunities for malicious actors to correlate user activities and build detailed profiles of online behavior.
The technical root cause of this vulnerability lies in Firefox's connection persistence mechanism for favicon requests. When a browser window is closed, the underlying network connections used for favicon resource retrieval should typically be terminated and cleaned up as part of normal resource management. However, in affected versions, these connections remain active and maintain their association with specific IP addresses and network endpoints. This persistent connection behavior creates a tracking vector where servers can observe the same client connection being reused across different browsing contexts, effectively allowing them to correlate multiple browsing sessions under a single persistent connection identifier.
The operational impact of this vulnerability extends beyond simple tracking capabilities and represents a sophisticated method for user fingerprinting and behavioral analysis. Attackers can leverage this flaw to monitor user navigation patterns by observing the network traffic patterns from multiple IP addresses that correspond to the same persistent connection. This tracking capability becomes particularly concerning when combined with other browser fingerprinting techniques, as it provides additional data points for creating unique user profiles. The vulnerability aligns with CWE-119 Improper Restriction of Operations within the Buffer Boundary, as it involves improper handling of network connection resources that extend beyond their intended operational boundaries.
From an adversarial perspective, this vulnerability enables persistent tracking mechanisms that can operate across different browsing sessions and window states, making it particularly dangerous for privacy-conscious users. The tracking capability persists even after window closure, which violates the expected behavior of browser connection management and creates opportunities for surveillance systems to maintain long-term user monitoring capabilities. This vulnerability also relates to ATT&CK technique T1566.002 Credential Access: Phishing, as it can be combined with phishing attacks to create more sophisticated tracking profiles that help attackers understand user behavior patterns and preferences.
The mitigation for this vulnerability requires immediate patching of affected Firefox versions to ensure proper connection cleanup and termination upon window closure. Browser vendors should implement stricter connection management policies that prevent persistent connections from remaining active after associated browsing contexts are closed. Additionally, users should be educated about the privacy implications of connection persistence and the importance of keeping browsers updated to prevent exploitation of such tracking mechanisms. Security configurations should include automatic cleanup of network resources and proper handling of connection lifecycle management to prevent unauthorized tracking through persistent connection reuse. The vulnerability demonstrates the importance of proper resource management in web browsers and highlights the need for comprehensive testing of connection handling mechanisms to prevent privacy leakage through seemingly innocuous features like favicon retrieval.