CVE-2006-1741 in Firefox
Summary
by MITRE
Mozilla Firefox 1.x before 1.5 and 1.0.x before 1.0.8, Mozilla Suite before 1.7.13, and SeaMonkey before 1.0 allows remote attackers to inject arbitrary Javascript into other sites by (1) "using a modal alert to suspend an event handler while a new page is being loaded", (2) using eval(), and using certain variants involving (3) "new Script;" and (4) using window.__proto__ to extend eval, aka "cross-site JavaScript injection".
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Analysis
by VulDB Data Team • 03/12/2021
This vulnerability represents a sophisticated cross-site scripting injection flaw that exploited the asynchronous nature of browser event handling and JavaScript execution. The vulnerability affected multiple Mozilla-based browsers including Firefox versions prior to 1.5, Mozilla Suite versions before 1.7.13, and SeaMonkey versions before 1.0. The core issue stemmed from how browsers handled modal dialog suspensions during page transitions, creating a window where malicious JavaScript could be injected into legitimate websites. The attack leveraged the modal alert mechanism to temporarily halt event processing while a new page loaded, allowing attackers to manipulate the execution context and inject malicious code. This technique specifically targeted the browser's event handling system where the suspension of one event handler could be exploited to execute arbitrary JavaScript in the context of another site.
The technical exploitation involved multiple attack vectors that demonstrated a deep understanding of JavaScript's prototype chain and execution environment. Attackers could utilize the eval() function in conjunction with window._proto_ to extend the functionality of eval, effectively bypassing security restrictions. The "new Script;" variant provided an alternative method for creating executable JavaScript code from strings, while the modal alert suspension technique created a timing window where attackers could inject malicious code that would execute in the context of the target website. This approach was particularly dangerous because it could be used to steal session cookies, perform unauthorized actions on behalf of users, or redirect users to malicious sites. The vulnerability was classified under CWE-79 as a cross-site scripting weakness, specifically targeting the improper handling of untrusted input in web applications.
The operational impact of this vulnerability was severe as it allowed attackers to perform session hijacking, data theft, and unauthorized actions on behalf of users without their knowledge. Users could be redirected to malicious sites, have their session information stolen, or be subjected to drive-by downloads that exploited other browser vulnerabilities. The attack required minimal user interaction beyond visiting a compromised website, making it particularly dangerous in phishing scenarios or when users visited malicious sites that could inject code into legitimate browsing sessions. The vulnerability was particularly concerning because it affected not just Firefox but also the broader Mozilla ecosystem, meaning that a single exploit could potentially compromise multiple browser implementations. Security researchers noted that this type of vulnerability represented a fundamental flaw in how browsers managed asynchronous execution contexts and event handling during page transitions.
Mitigation strategies focused on patching the underlying browser implementations and implementing proper input sanitization. The most effective solution was updating to the patched versions of Firefox 1.5, Mozilla Suite 1.7.13, and SeaMonkey 1.0, which addressed the modal alert suspension handling and improved the security of JavaScript execution contexts. Browser vendors implemented stricter controls over eval() function usage and enhanced the prototype chain protection mechanisms. Organizations should have implemented comprehensive browser update policies and deployed security monitoring systems to detect potential exploitation attempts. The vulnerability highlighted the importance of understanding asynchronous execution contexts in web browsers and led to improvements in how browser security models handle event handling during page transitions. This incident contributed to the development of more robust security measures in modern browsers, including better isolation between different browsing contexts and enhanced protection against prototype manipulation attacks. The vulnerability also emphasized the need for proper sandboxing mechanisms in JavaScript engines and reinforced the principle that browser security models must account for complex asynchronous execution patterns.