CVE-2006-2056 in Internet Explorer
Summary
by MITRE
Argument injection vulnerability in Internet Explorer 6 for Windows XP SP2 allows user-assisted remote attackers to modify command line arguments to an invoked mail client via " (double quote) characters in a mailto: scheme handler, as demonstrated by launching Microsoft Outlook with an arbitrary filename as an attachment. NOTE: it is not clear whether this issue is implementation-specific or a problem in the Microsoft API.
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Analysis
by VulDB Data Team • 05/07/2019
This vulnerability represents a critical argument injection flaw in Internet Explorer 6 running on Windows XP Service Pack 2 that exploits the mailto: scheme handler functionality. The vulnerability occurs when user-supplied input containing double quote characters is processed by the browser's mailto handler, allowing malicious actors to manipulate command line arguments passed to the system's default mail client. The attack requires user interaction as the target must click on a specially crafted hyperlink, making this a user-assisted remote code execution vector. The specific technical mechanism involves the improper handling of special characters within the mailto URI, where double quotes are not properly escaped or sanitized before being passed to the underlying mail client process.
The operational impact of this vulnerability extends beyond simple command injection, as it enables attackers to manipulate how the mail client launches and processes attachments. When Microsoft Outlook is invoked through the vulnerable mailto handler, an attacker can potentially force the application to open arbitrary files as attachments, effectively bypassing normal security boundaries. This type of vulnerability falls under the CWE-77 category of command injection, specifically targeting argument injection in external command execution contexts. The vulnerability demonstrates a classic improper input validation issue where the application fails to properly sanitize user-provided data before incorporating it into system calls.
The attack vector relies on the trust model between the web browser and the operating system's mail client integration, where the browser acts as an intermediary that translates web-based mailto links into system commands. When a user clicks on a malicious mailto link containing specially crafted double quotes, the browser passes these characters directly to the mail client without proper sanitization, potentially allowing attackers to inject additional command line arguments or manipulate file paths. This vulnerability is particularly concerning because it operates at the system integration layer, where web browsers interface with native applications, making it a prime target for privilege escalation attacks. The issue's implementation-specific nature suggests it may be related to how Microsoft's API handles URI parsing and command line argument construction.
Mitigation strategies should focus on both browser-level and system-level protections. Users should avoid clicking on untrusted mailto links and maintain updated security patches for their operating systems and applications. Browser vendors should implement proper input sanitization for URI handlers and consider sandboxing mechanisms that prevent external command injection. System administrators should monitor for unusual mail client behavior and implement application whitelisting policies to restrict which applications can be launched through web-based interfaces. The vulnerability also highlights the importance of proper API design and input validation in system integration points, as outlined in security best practices for preventing injection attacks. Organizations should also consider implementing web application firewalls that can detect and block suspicious URI patterns that may indicate exploitation attempts. This vulnerability serves as a reminder of the inherent risks in web-to-native application integration and the need for comprehensive security testing across all interface points between different software layers.