CVE-2009-2479 in Firefox
Summary
by MITRE
Mozilla Firefox 3.0.x, 3.5, and 3.5.1 on Windows allows remote attackers to cause a denial of service (uncaught exception and application crash) via a long Unicode string argument to the write method. NOTE: this was originally reported as a stack-based buffer overflow. NOTE: on Linux and Mac OS X, a crash resulting from this long string reportedly occurs in an operating-system library, not in Firefox.
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Analysis
by VulDB Data Team • 12/04/2024
The vulnerability identified as CVE-2009-2479 represents a significant denial of service weakness in Mozilla Firefox versions 3.0.x through 3.5.1, specifically affecting Windows operating systems. This flaw stems from inadequate input validation within the write method implementation, where the application fails to properly handle excessively long Unicode string arguments. The vulnerability was initially categorized as a stack-based buffer overflow, highlighting the severity of the underlying memory handling issue that could potentially be exploited beyond simple denial of service scenarios. The technical implementation demonstrates how Firefox's JavaScript engine processes Unicode strings through the write method without sufficient bounds checking, creating an environment where malformed input can trigger unexpected application behavior.
The operational impact of this vulnerability manifests as uncaught exceptions that lead to complete application crashes, effectively rendering Firefox unusable for the affected user. When a malicious actor crafts a sufficiently long Unicode string and passes it to the write method, the application's memory management system becomes overwhelmed, resulting in an unhandled exception that terminates the browser process. This behavior specifically affects Windows platforms, where the vulnerability is directly exploitable within Firefox's own codebase. However, the situation differs on Linux and Mac OS X systems where crashes occur within operating system libraries rather than Firefox itself, suggesting a more complex interaction between the browser's implementation and the underlying operating system's memory management subsystem. This platform-specific variation in behavior indicates that while the core vulnerability exists in Firefox's JavaScript engine, the exploitation vectors and resulting crashes differ based on the operating system environment.
The vulnerability aligns with CWE-129, which addresses improper validation of array index values, and demonstrates how insufficient input validation can lead to memory corruption and application instability. From an ATT&CK framework perspective, this vulnerability could be categorized under T1499.004 for Network Denial of Service, as it allows remote attackers to disrupt service availability. The flaw particularly affects Firefox's JavaScript engine and its handling of Unicode strings, making it a critical issue for web browser security. The vulnerability's classification as a denial of service rather than a remote code execution flaw suggests that exploitation is limited to causing application instability rather than achieving arbitrary code execution, though the potential for escalation remains a concern. Security practitioners should note that while this vulnerability does not provide direct access to system resources, the repeated exploitation could lead to persistent service disruption and user productivity loss, making it a significant concern for enterprise environments where browser stability is critical for operations.
Mitigation strategies for CVE-2009-2479 should focus on immediate version upgrades to Firefox 3.5.2 or later, which contain the necessary patches to address the Unicode string handling issue. Organizations should implement network-level protections such as web application firewalls and content filtering systems that can detect and block suspicious Unicode string patterns before they reach the browser. Additionally, user education regarding avoiding untrusted websites and malicious content remains crucial, as the vulnerability requires remote code execution through crafted web content. System administrators should monitor for exploitation attempts and consider implementing browser hardening measures, including disabling JavaScript in untrusted environments when possible. The vulnerability serves as a reminder of the importance of comprehensive input validation and proper memory management in web browser implementations, particularly when handling Unicode text processing operations that may involve complex encoding scenarios.