CVE-2009-2953 in Firefox
Summary
by MITRE
Mozilla Firefox 3.0.6 through 3.0.13, and 3.5.x, allows remote attackers to cause a denial of service (CPU consumption) via JavaScript code with a long string value for the hash property (aka location.hash), a related issue to CVE-2008-5715.
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Analysis
by VulDB Data Team • 10/01/2025
This vulnerability affects Mozilla Firefox versions 3.0.6 through 3.0.13 and 3.5.x branches, representing a significant denial of service weakness that can be exploited remotely through JavaScript code manipulation. The flaw specifically targets the handling of the hash property within the location object, where attackers can craft malicious JavaScript code that sets an extremely long string value to location.hash. This particular vulnerability is categorized under CWE-400 as an Uncontrolled Resource Consumption, which directly impacts system performance and availability. The issue is closely related to CVE-2008-5715, indicating a pattern of similar vulnerabilities in Firefox's JavaScript engine handling of URL components, particularly hash values that are processed and potentially stored in memory.
The technical execution of this attack involves JavaScript code that manipulates the location.hash property with an extraordinarily long string, typically in the range of thousands or tens of thousands of characters. When Firefox processes this malformed hash value, its JavaScript engine enters an inefficient loop during string processing and memory allocation, causing excessive CPU utilization that can reach 100% on the affected system. This behavior occurs because the browser's internal string handling mechanisms do not properly validate or limit the length of hash values before processing them, leading to resource exhaustion that can render the browser unresponsive or cause system-wide performance degradation. The vulnerability operates at the application level, leveraging the browser's JavaScript engine to consume system resources without requiring any special privileges or user interaction beyond visiting a malicious webpage.
The operational impact of this vulnerability extends beyond simple browser instability to potentially affect entire system performance, especially in environments where multiple browser instances are running simultaneously or when the targeted system is already under resource constraints. Attackers can exploit this weakness through various delivery mechanisms including malicious websites, phishing campaigns, or compromised web applications that inject the malicious JavaScript payload. The attack vector is particularly dangerous because it can be executed silently without user interaction, making it difficult to detect and prevent through traditional user awareness measures. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 (Network Denial of Service) and T1059.007 (JavaScript), demonstrating how web-based attacks can leverage browser-specific implementation flaws to achieve system-level disruption.
Mitigation strategies for this vulnerability include immediate patching of affected Firefox versions to the latest available releases, which contain fixes for the string handling and resource consumption issues. Organizations should implement browser hardening policies that include JavaScript execution restrictions and resource monitoring to detect unusual CPU usage patterns. Network-based mitigations such as web application firewalls can help detect and block malicious JavaScript payloads, while browser security extensions can provide additional layers of protection. System administrators should monitor for abnormal CPU utilization patterns that may indicate exploitation attempts, and consider implementing sandboxing techniques to limit the impact of successful attacks. The vulnerability also highlights the importance of regular security assessments and vulnerability management programs to identify and remediate similar weaknesses in browser implementations before they can be exploited by adversaries.