CVE-2008-4381 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 7 allows remote attackers to cause a denial of service (application crash) via Javascript that calls the alert function with a URL-encoded string of a large number of invalid characters.
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Analysis
by VulDB Data Team • 08/02/2021
Microsoft Internet Explorer 7 contains a vulnerability that enables remote attackers to trigger a denial of service condition through carefully crafted javascript code. This flaw specifically manifests when the alert function is invoked with a URL-encoded string containing an excessive number of invalid characters. The vulnerability stems from insufficient input validation and sanitization within the browser's javascript engine, which fails to properly handle malformed character sequences during alert dialog processing. When the browser encounters such malformed input, it crashes and terminates the application, resulting in a denial of service condition that affects legitimate users attempting to access the affected system.
The technical implementation of this vulnerability leverages the alert function's handling of string parameters, particularly when those parameters contain URL-encoded sequences that the browser cannot properly interpret or render. The flaw operates at the javascript runtime level where invalid character sequences cause memory corruption or stack overflow conditions within the browser's execution environment. This behavior aligns with common software security weaknesses categorized under CWE-129, which addresses improper validation of input boundaries, and CWE-170, which covers improper handling of potentially dangerous input sequences. The vulnerability represents a classic case of inadequate input sanitization where the browser fails to implement proper bounds checking or character validation before processing user-supplied javascript code.
The operational impact of this vulnerability extends beyond simple application instability, as it can be exploited remotely through web pages or malicious scripts that automatically trigger the problematic javascript code. Attackers can craft web content that, when loaded in Internet Explorer 7, automatically executes the malicious alert call with malformed parameters, causing the browser to crash without requiring any user interaction beyond visiting the compromised page. This makes the vulnerability particularly dangerous in web-based attack scenarios where users may unknowingly encounter malicious content. The attack vector falls under the ATT&CK technique T1211, which involves exploitation of software vulnerabilities to cause system instability, and T1059, which covers execution through scripting languages. The vulnerability affects the browser's user experience and can potentially be used as a component in larger attack campaigns where the primary goal is to disrupt services or force users to abandon the browser.
Mitigation strategies for this vulnerability include implementing proper input validation at multiple layers of the application stack, including browser-side javascript execution environments and server-side content filtering. Organizations should consider deploying web application firewalls that can detect and block malicious javascript patterns before they reach the browser, as well as implementing browser security policies that restrict potentially dangerous javascript functions. The most effective long-term solution involves upgrading to newer versions of Internet Explorer or migrating to more secure browser platforms that have addressed this specific vulnerability. Additionally, security patches and updates from Microsoft should be applied immediately when available, as this vulnerability represents a known weakness that has been documented and remediated in subsequent software versions. Network administrators should also consider implementing content security policies that prevent execution of untrusted javascript code and monitor for suspicious traffic patterns that may indicate exploitation attempts.