CVE-2004-0475 in Internet Explorer
Summary
by MITRE
The showHelp function in Internet Explorer 6 on Windows XP Pro allows remote attackers to execute arbitrary local .CHM files via a double backward slash ("\\") before the target CHM file, as demonstrated using an "ms-its" URL to ntshared.chm. NOTE: this bug may overlap CVE-2003-1041.
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Analysis
by VulDB Data Team • 06/29/2021
The vulnerability described in CVE-2004-0475 represents a significant security flaw in Internet Explorer 6 running on Windows XP Professional systems. This issue specifically affects the showHelp function within the browser's help system implementation, creating a path for remote code execution through maliciously crafted hyperlinks. The vulnerability exploits a path traversal mechanism that allows attackers to bypass normal file access restrictions and execute arbitrary local .CHM (Compiled HTML Help) files from the victim's system. The attack vector utilizes an "ms-its" URL scheme combined with a double backward slash sequence that manipulates how Internet Explorer resolves file paths, effectively enabling remote attackers to access and execute local help files that would normally be restricted.
The technical implementation of this vulnerability stems from improper input validation within Internet Explorer's help system component. When processing ms-its URLs, the browser fails to properly sanitize path specifications that contain double backward slashes, allowing an attacker to craft malicious URLs that can traverse the file system and execute local CHM files. This flaw operates at the application level within the browser's help subsystem and demonstrates a classic path traversal vulnerability that can be exploited to gain unauthorized access to local system resources. The vulnerability is particularly dangerous because it leverages legitimate system components to execute malicious code, making detection more challenging for security monitoring systems that might not flag normal help system behavior as suspicious.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with a means to perform arbitrary file operations on vulnerable systems. Attackers can leverage this vulnerability to execute malicious CHM files that may contain embedded ActiveX controls or other malicious code, potentially leading to full system compromise. The fact that this vulnerability affects Windows XP Professional systems, which were widely deployed in corporate environments at the time, amplified the potential damage. Security researchers have noted that this issue overlaps with CVE-2003-1041, indicating that similar path traversal mechanisms may exist in other components of the same software stack. The vulnerability operates at the system level, potentially allowing attackers to execute commands with the privileges of the logged-in user, though not necessarily with administrative rights.
Mitigation strategies for this vulnerability require immediate patching of Internet Explorer 6 installations with Microsoft security updates, as well as implementing network-level restrictions on access to help system components. Organizations should disable the help system functionality where possible and implement strict access controls on CHM files within the system. From a cybersecurity perspective, this vulnerability aligns with CWE-22 Path Traversal and represents a technique that attackers might use to establish persistent access to compromised systems. The ATT&CK framework categorizes this type of vulnerability under the T1211 Exploitation for Privilege Escalation tactic, as it allows attackers to execute code with elevated privileges through legitimate system components. System administrators should also consider implementing application whitelisting policies to prevent execution of unauthorized CHM files and monitor network traffic for suspicious ms-its URL patterns that could indicate exploitation attempts.