CVE-2009-2954 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 6.0.2900.2180 and earlier allows remote attackers to cause a denial of service (CPU consumption and application hang) 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 • 04/07/2017
Microsoft Internet Explorer versions 6.0.2900.2180 and earlier contain a critical vulnerability that enables remote attackers to execute denial of service attacks through carefully crafted JavaScript code. This vulnerability specifically targets the hash property of the location object, which is commonly used to manipulate URL fragments and maintain application state. The flaw occurs when JavaScript code passes an excessively long string value to the location.hash property, causing the browser to consume excessive CPU resources and ultimately hang the application. This vulnerability represents a classic example of a resource exhaustion attack where malicious actors can exploit the browser's handling of URL fragments to degrade system performance and availability.
The technical root cause of this vulnerability lies in the improper validation and handling of string inputs within the JavaScript engine of Internet Explorer. When a JavaScript application attempts to set an extremely long string value to the location.hash property, the browser's internal parsing and processing mechanisms become overwhelmed. The browser must process and potentially encode the lengthy string value, which can trigger recursive operations or inefficient memory allocation patterns. This issue is particularly dangerous because it can be triggered through web pages loaded over HTTP or HTTPS, making it accessible to attackers without requiring any special privileges or user interaction beyond visiting a malicious website. The vulnerability is categorized under CWE-400 as an uncontrolled resource consumption flaw, where the system fails to properly limit resource usage during processing of malicious inputs.
The operational impact of this vulnerability extends beyond simple application hanging, as it can effectively render the affected browser instance unusable for legitimate web browsing activities. Attackers can craft malicious web pages that automatically trigger this vulnerability when loaded, causing the browser to consume 100% CPU cycles and become unresponsive. This can lead to complete system unavailability if the user is running multiple browser instances or if the vulnerability is exploited in a targeted manner against specific users. The vulnerability directly impacts the availability aspect of the CIA triad, as it can be used to deny service to legitimate users by consuming system resources. From an attacker's perspective, this represents a low-effort, high-impact vector that requires minimal privileges and can be easily deployed through standard web delivery mechanisms.
The remediation strategy for this vulnerability involves implementing proper input validation and resource limiting within the JavaScript engine. Microsoft addressed this issue through security updates that introduced bounds checking for string values assigned to the location.hash property, preventing the execution of overly long strings that could cause resource exhaustion. Organizations should implement the latest security patches and updates for Internet Explorer to protect against this vulnerability. Additionally, administrators should consider implementing browser security policies that restrict the execution of potentially malicious JavaScript code and monitor for unusual CPU consumption patterns. The vulnerability also highlights the importance of proper error handling and resource management in web browser implementations, as outlined in various security frameworks and best practices for secure coding. This issue serves as a reminder that even seemingly benign features like URL fragment handling can become attack vectors when not properly secured against resource exhaustion attacks.