CVE-2009-3988 in Firefox
Summary
by MITRE
Mozilla Firefox 3.0.x before 3.0.18 and 3.5.x before 3.5.8, and SeaMonkey before 2.0.3, does not properly restrict read access to object properties in showModalDialog, which allows remote attackers to bypass the Same Origin Policy and conduct cross-site scripting (XSS) attacks via crafted dialogArguments values.
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Analysis
by VulDB Data Team • 05/01/2026
The vulnerability identified as CVE-2009-3988 represents a critical security flaw in Mozilla Firefox and SeaMonkey browsers that undermines fundamental web security mechanisms. This issue affects Firefox versions 3.0.x prior to 3.0.18 and 3.5.x prior to 3.5.8, along with SeaMonkey versions before 2.0.3, creating a significant attack surface that malicious actors could exploit to circumvent core web security protections. The flaw specifically resides in the showModalDialog function's handling of dialogArguments parameters, which should normally enforce strict access controls between different origins.
The technical implementation of this vulnerability stems from improper object property access restrictions within the showModalDialog API. When developers use showModalDialog to create modal dialogs, the dialogArguments parameter contains data that should be isolated from the calling script's context to prevent unauthorized access to sensitive information. However, Firefox's implementation failed to properly enforce these access controls, allowing attackers to craft malicious dialogArguments values that could expose object properties across origin boundaries. This breakdown in access control mechanisms directly violates the fundamental Same Origin Policy that forms the cornerstone of web security architecture.
The operational impact of this vulnerability extends far beyond simple cross-site scripting capabilities, as it provides attackers with the means to bypass essential security boundaries that protect user data and system integrity. An attacker could leverage this flaw to execute malicious scripts in the context of different origins, potentially accessing cookies, local storage, or other sensitive data that should remain isolated between domains. This vulnerability enables sophisticated attack scenarios where malicious actors could harvest user credentials, session tokens, or other confidential information from legitimate websites, particularly those that rely on modal dialog interfaces for user interactions or form submissions.
From a threat modeling perspective, this vulnerability aligns with CWE-200 (Information Exposure) and CWE-352 (Cross-Site Request Forgery) categories, representing a direct violation of the principle of least privilege in web browser security. The ATT&CK framework categorizes this as a technique for privilege escalation and information gathering, as it allows adversaries to access resources that should be restricted to specific origins. The vulnerability's exploitation typically requires social engineering to convince users to visit malicious websites, but once triggered, it can lead to persistent security breaches that compromise user sessions and sensitive data across multiple web applications.
Mitigation strategies for CVE-2009-3988 primarily involve immediate patching of affected browser versions, as the vulnerability cannot be effectively addressed through client-side configuration changes alone. Organizations should implement comprehensive browser update policies and monitor for vulnerable installations in their environments. Additionally, web developers should avoid relying on showModalDialog for critical security functions and implement additional input validation for dialog arguments. Network security controls such as web application firewalls and content filtering systems can provide supplementary protection, though they cannot fully compensate for the underlying browser vulnerability. The remediation process requires careful attention to ensure that updates don't introduce compatibility issues with existing web applications while maintaining the security posture against this specific class of cross-site scripting attacks.