CVE-2007-3576 in Internet Explorer
Summary
by MITRE
** DISPUTED ** Microsoft Internet Explorer 6 executes web script from URIs of arbitrary scheme names ending with the "script" character sequence, using the (1) vbscript: handler for scheme names with 7 through 9 characters, and the (2) javascript: handler for scheme names with 10 or more characters, which might allow remote attackers to bypass certain XSS protection schemes. NOTE: other researchers dispute the significance of this issue, stating "this only works when typed in the address bar."
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Analysis
by VulDB Data Team • 08/08/2024
This vulnerability exists in Microsoft Internet Explorer 6 and relates to how the browser handles URI schemes that end with the character sequence "script". The flaw operates through a specific parsing mechanism where the browser automatically invokes script execution handlers based on the length of the scheme name. When a URI scheme name contains between seven and nine characters and ends with "script", the browser employs the vbscript: handler to execute the embedded script content. Conversely, when the scheme name contains ten or more characters and ends with "script", the javascript: handler is invoked instead. This behavior represents a fundamental flaw in the browser's URI scheme parsing logic that bypasses normal security boundaries.
The technical exploitation of this vulnerability occurs when a user visits a maliciously crafted URI that leverages this scheme parsing behavior. The vulnerability's significance stems from its ability to circumvent cross-site scripting protection mechanisms that rely on proper URI scheme validation. Attackers can craft URLs where the scheme name ends with "script" but contains additional characters that make the length classification trigger either the vbscript or javascript execution handlers. This creates a scenario where user-supplied content can be interpreted as executable script code rather than benign URI data, effectively allowing for code execution in the context of the user's browser session.
The operational impact of this vulnerability extends beyond simple script execution, as it can be leveraged to bypass security controls that depend on URI scheme validation. When combined with other attack vectors, this vulnerability could enable attackers to perform actions such as stealing session cookies, redirecting users to malicious sites, or executing arbitrary commands within the browser context. The vulnerability's disputed nature regarding its practical exploitability stems from the requirement for users to manually enter the malicious URI in the address bar, which limits its effectiveness in typical phishing or drive-by download scenarios. However, the underlying technical flaw remains a legitimate security concern that demonstrates the importance of proper URI parsing and validation in web browsers.
Security professionals should consider this vulnerability in the context of broader web application security principles and the importance of input validation. The issue aligns with common weakness enumerations related to improper input validation and insecure parsing mechanisms. From an att&ck framework perspective, this vulnerability could be categorized under initial access and execution tactics, potentially enabling further compromise through code execution. Organizations should ensure that legacy systems running Internet Explorer 6 are properly isolated and that users are educated about the risks of manually entering untrusted URLs. The vulnerability also highlights the importance of maintaining up-to-date browser versions and implementing additional security layers such as content security policies to prevent exploitation of similar parsing issues.