CVE-2006-6578 in IIS
Summary
by MITRE
Microsoft Internet Information Services (IIS) 5.1 permits the IUSR_Machine account to execute non-EXE files such as .COM files, which allows attackers to execute arbitrary commands via arguments to any .COM file that executes those arguments, as demonstrated using win.com when it is in a web directory with certain permissions.
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Analysis
by VulDB Data Team • 04/13/2019
Microsoft Internet Information Services version 5.1 contains a critical security flaw that stems from improper file execution permissions within its web server configuration. This vulnerability specifically affects the IUSR_Machine account which serves as the default anonymous user account for IIS 5.1 installations. The flaw allows this account to execute non-EXE files such as .COM files, creating an avenue for arbitrary code execution that can be exploited by malicious actors. The vulnerability is particularly dangerous because it leverages the inherent design of IIS 5.1's permission model where certain executable file types are not properly restricted for anonymous users.
The technical implementation of this vulnerability involves the exploitation of the win.com file which is a Windows command file that can execute system commands when invoked through the web server environment. When win.com is placed within a web directory that grants the IUSR_Machine account execute permissions, attackers can manipulate the command line arguments passed to this file to execute arbitrary system commands. This represents a classic command injection vulnerability where the web server's execution context is leveraged to run unauthorized code with the privileges of the IIS service account. The flaw is categorized under CWE-78 as a failure to properly sanitize command line arguments, allowing for command injection attacks that can be executed through the web interface.
The operational impact of this vulnerability is severe as it provides attackers with a straightforward path to gain unauthorized access to the underlying system. Once exploited, attackers can execute commands with the same privileges as the IIS service, potentially leading to complete system compromise. The vulnerability affects all IIS 5.1 installations and can be exploited remotely through web-based attacks without requiring any special authentication credentials. This makes it particularly attractive to attackers who can leverage it for privilege escalation, data exfiltration, or to establish persistent access to the compromised system. The vulnerability demonstrates a fundamental flaw in IIS 5.1's security model where file execution permissions are not properly enforced for anonymous access accounts.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1059 which describes the use of command and scripting interpreters for execution. The attack chain typically involves placing a malicious .COM file in a web-accessible directory, setting appropriate permissions, and then invoking the file through web requests to execute arbitrary commands. The vulnerability also relates to T1078 which covers legitimate credentials usage, as attackers can leverage the existing IUSR_Machine account permissions rather than needing to establish new authentication mechanisms. Organizations running IIS 5.1 should implement immediate mitigations including restricting anonymous access permissions, disabling unnecessary file execution capabilities, and implementing proper network segmentation to limit the attack surface. Additionally, the use of modern security controls such as application whitelisting and web application firewalls can help prevent exploitation attempts.
The vulnerability highlights the importance of proper privilege separation in web server configurations and demonstrates how default security settings can create dangerous execution paths. The flaw represents a design issue in IIS 5.1's permission model where the default configuration does not adequately restrict what types of files can be executed by anonymous users. Organizations should ensure that all IIS installations are properly configured with the principle of least privilege, limiting what files can be executed and what commands can be invoked through the web server interface. This vulnerability also underscores the need for regular security assessments and the importance of keeping web server software updated to address known security flaws that may exist in older versions.