CVE-2007-3736 in Firefox
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in Mozilla Firefox before 2.0.0.5 allows remote attackers to inject arbitrary web script "into another site s context" via a "timing issue" involving the (1) addEventListener or (2) setTimeout function, probably by setting events that activate after the context has changed.
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Analysis
by VulDB Data Team • 07/22/2019
This cross-site scripting vulnerability exists in mozilla firefox versions prior to 200.0.5 and represents a sophisticated timing-based attack vector that exploits the browser's event handling mechanisms. The flaw specifically targets the addEventListener and setTimeout functions, which are fundamental components of javascript execution in web browsers. Attackers can leverage this vulnerability by crafting malicious scripts that set up events or timeouts that execute after a context change has occurred, effectively allowing them to inject arbitrary web script code into another site's context. This timing issue creates a window where the browser's security model is temporarily bypassed, enabling attackers to execute malicious code within the target domain's security boundaries.
The technical exploitation of this vulnerability stems from the browser's handling of asynchronous event execution and context switching mechanisms. When javascript code is executed in firefox, the browser maintains a specific execution context that defines the security boundaries for script execution. However, the timing issue allows attackers to schedule events that execute after the context has already changed, potentially from one domain to another. This creates a race condition where the event handler executes in a different security context than when it was originally registered, effectively circumventing the same-origin policy that normally protects against cross-site scripting attacks.
The operational impact of this vulnerability extends beyond simple script injection, as it can enable attackers to perform a wide range of malicious activities including session hijacking, data theft, and credential harvesting. When an attacker successfully exploits this vulnerability, they can inject scripts that access cookies, localStorage, and other sensitive data that should be restricted to the original site's context. The vulnerability's classification under CWE-79 indicates it represents a classic cross-site scripting weakness, while its exploitation pattern aligns with ATT&CK technique T1059.007 for script-based execution. The timing-based nature of the attack makes it particularly difficult to detect through traditional security monitoring approaches, as the malicious script execution occurs at a specific moment in the browser's event processing cycle rather than during initial page load.
Mitigation strategies for this vulnerability require both immediate patching and defensive programming practices. Organizations should prioritize updating firefox installations to version 2.0.0.5 or later, where this vulnerability has been addressed through improved event handling and context management. Additionally, developers should implement proper input validation and output encoding for all user-supplied data, particularly when dealing with javascript event handlers. The browser's security model should be enhanced through stricter enforcement of context boundaries during event processing, ensuring that events scheduled via addEventListener or setTimeout cannot execute outside their original security context. Network-level protections such as content security policies can provide additional defense-in-depth, though the most effective mitigation remains the timely application of vendor security patches. This vulnerability demonstrates the critical importance of proper asynchronous execution handling in web browsers and highlights how seemingly benign timing issues can create significant security risks when combined with event-driven programming models.