CVE-2004-1376 in Internet Explorer
Summary
by MITRE
Directory traversal vulnerability in Microsoft Internet Explorer 5.01, 5.5, and 6.0 allows remote malicious FTP servers to overwrite arbitrary files via .. (dot dot) sequences in filenames returned from a LIST command.
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Analysis
by VulDB Data Team • 04/07/2017
This vulnerability represents a critical directory traversal flaw in Microsoft Internet Explorer versions 5.01, 5.5, and 6.0 that specifically targets the handling of FTP protocol responses. The issue manifests when Internet Explorer processes filenames returned from FTP LIST commands, where malicious FTP servers can craft responses containing .. (dot dot) sequences that instruct the browser to navigate outside of the intended download directory. This fundamental flaw in input validation and path resolution allows attackers to manipulate file system operations beyond the expected boundaries. The vulnerability falls under CWE-22 which categorizes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. From an operational perspective, this vulnerability enables remote code execution and system compromise by allowing malicious actors to overwrite critical system files, create backdoors, or inject malicious content into the victim's file system. The attack vector specifically exploits the trust relationship between the browser and FTP servers, leveraging the fact that Internet Explorer does not properly sanitize or validate the paths contained within FTP LIST responses before attempting file operations.
The technical implementation of this vulnerability occurs at the application layer where Internet Explorer's FTP client component fails to properly process directory navigation sequences in filenames returned by FTP servers. When a malicious FTP server responds to a LIST command with filenames containing .. sequences, the browser interprets these as directory traversal commands rather than literal filenames, effectively bypassing normal file system access controls. This flaw exploits the underlying assumption that FTP server responses are trustworthy and properly formatted, without implementing adequate input sanitization or path validation mechanisms. The vulnerability is particularly dangerous because it operates at the point where the browser processes server responses, meaning that even legitimate FTP servers with malformed responses could potentially trigger this behavior. This type of attack aligns with ATT&CK technique T1190 which describes exploiting vulnerabilities in network infrastructure and client applications to gain unauthorized access to systems. The impact extends beyond simple file overwrites to include complete system compromise, as attackers can leverage this vulnerability to place malicious executables in system directories, modify security-related files, or establish persistent access mechanisms.
The operational impact of CVE-2004-1376 is severe and multifaceted, affecting organizations that rely on older Internet Explorer versions for file transfers or web browsing activities. Attackers can exploit this vulnerability to gain unauthorized access to systems, potentially leading to data breaches, system infiltration, and complete compromise of affected environments. The vulnerability particularly affects enterprise environments where legacy systems may still be running older Internet Explorer versions, creating persistent security risks that can be exploited by attackers with minimal technical skill. Organizations with web applications or services that depend on FTP functionality for file management face significant exposure, as this vulnerability can be leveraged to execute arbitrary commands on target systems. The attack requires minimal privileges from the attacker's perspective since it exploits a flaw in the client-side browser behavior rather than requiring authentication to the target system. Security professionals should consider this vulnerability as part of broader network security assessments, particularly in environments where outdated browser versions are still in use. Mitigation strategies include immediate patching of affected Internet Explorer versions, implementation of network segmentation to limit FTP server access, and deployment of network monitoring solutions to detect suspicious FTP LIST command responses containing traversal sequences. The vulnerability also highlights the importance of proper input validation and the principle of least privilege in application design, as the flaw could have been prevented through proper sanitization of server responses before file system operations are performed.