CVE-2009-2576 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 and memory consumption) via a long Unicode string argument to the write method, a related issue to CVE-2009-2479. NOTE: it was later reported that 7.0.6000.16473 and earlier are also affected.
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Analysis
by VulDB Data Team • 08/12/2021
This vulnerability affects Microsoft Internet Explorer versions 6.0.2900.2180 and earlier, with additional impact on version 7.0.6000.16473 and earlier, representing a significant denial of service weakness that can be exploited remotely. The flaw specifically targets the write method within the browser's JavaScript engine, where a maliciously crafted long Unicode string argument can trigger excessive resource consumption. This vulnerability falls under the category of resource exhaustion attacks that can cause system instability and performance degradation. The issue is particularly concerning as it represents a related problem to CVE-2009-2479, indicating a pattern of similar vulnerabilities in Internet Explorer's handling of Unicode strings within JavaScript methods. The vulnerability operates by exploiting how the browser processes Unicode characters in the write method, leading to continuous CPU and memory consumption that can ultimately render the system unresponsive or cause the browser to crash entirely.
The technical implementation of this vulnerability involves the manipulation of Unicode string arguments passed to the write method, which causes the browser's JavaScript engine to allocate excessive memory resources and consume CPU cycles in an inefficient manner. When a long Unicode string is processed through this method, the underlying parsing and rendering mechanisms become overwhelmed, leading to resource exhaustion that can be leveraged by remote attackers to disrupt normal system operations. This behavior aligns with CWE-400, which categorizes unchecked resource consumption as a critical weakness in software systems. The vulnerability demonstrates a classic example of how improper input validation can lead to resource exhaustion, where the browser fails to properly limit or sanitize the length of Unicode strings before processing them through the write method. The attack vector is particularly dangerous because it can be executed remotely without requiring any special privileges or user interaction beyond visiting a malicious webpage.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be used to disrupt legitimate user sessions and potentially cause system-wide instability. When exploited, the vulnerability causes continuous high CPU usage and memory allocation that can prevent other applications from functioning properly, effectively creating a denial of service condition for the entire system. The affected versions of Internet Explorer represent a significant attack surface given their widespread deployment in enterprise environments and legacy systems. This vulnerability can be particularly problematic in corporate networks where multiple users may be simultaneously affected, leading to cascading service disruptions that impact business operations. The memory consumption aspect of this vulnerability can also lead to system crashes or forced reboots, especially on systems with limited resources, making it a particularly dangerous threat in environments where system stability is paramount.
Mitigation strategies for this vulnerability should focus on immediate remediation through Microsoft security updates and patches that address the underlying JavaScript engine flaw. Organizations should prioritize updating Internet Explorer to versions that contain the necessary security fixes, as this vulnerability was addressed in subsequent releases that properly handled Unicode string length validation. Network administrators should consider implementing browser isolation techniques and restricting access to potentially malicious websites through web filtering solutions. The vulnerability also underscores the importance of regular security assessments and vulnerability management programs that can identify and remediate similar issues before they can be exploited. Additionally, implementing monitoring solutions that can detect unusual CPU and memory consumption patterns may help identify exploitation attempts. This vulnerability highlights the critical need for proper input validation and resource management in web browsers, particularly when handling Unicode characters, and serves as a reminder of the ongoing challenges in securing complex software systems against resource exhaustion attacks. The remediation efforts should also include educating users about the risks of visiting untrusted websites and the importance of maintaining up-to-date software versions to prevent exploitation of known vulnerabilities.