CVE-2002-0421 in IIS
Summary
by MITRE
IIS 4.0 allows local users to bypass the "User cannot change password" policy for Windows NT by directly calling .htr password changing programs in the /iisadmpwd directory, including (1) aexp2.htr, (2) aexp2b.htr, (3) aexp3.htr , or (4) aexp4.htr.
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Analysis
by VulDB Data Team • 05/16/2019
The vulnerability described in CVE-2002-0421 represents a critical security flaw in Microsoft Internet Information Services version 4.0 running on Windows NT systems. This issue specifically targets the authentication and authorization mechanisms within IIS, where local users can exploit a design weakness to circumvent password policy enforcement. The vulnerability exists in the implementation of the IIS Admin service password change functionality, which was intended to provide a secure method for users to update their credentials while maintaining system security policies.
The technical flaw manifests through the direct invocation of specific handler files located in the /iisadmpwd virtual directory of IIS 4.0 installations. These files including aexp2.htr, aexp2b.htr, aexp3.htr, and aexp4.htr are part of Microsoft's IIS administration password change utility. When these files are called directly by local users, they bypass the normal authentication checks that should enforce the "User cannot change password" policy. This direct access allows attackers to modify user passwords without proper authorization, effectively undermining the security controls that should prevent unauthorized changes to user credentials. The vulnerability stems from insufficient access controls and input validation within the IIS handler processing mechanism.
The operational impact of this vulnerability is significant as it provides local attackers with an unauthorized method to modify user passwords, potentially leading to privilege escalation and persistent access to systems. Attackers can leverage this weakness to change passwords for any user account on the system, including administrative accounts, which could result in complete system compromise. The vulnerability is particularly dangerous because it operates at the local user level, meaning that any user with access to the system can exploit it without requiring remote network access or additional privileges. This creates a scenario where local users can effectively bypass the fundamental security principle that prevents users from changing their own passwords when such changes should be restricted by policy. The exploitation of this vulnerability aligns with attack patterns documented in the MITRE ATT&CK framework under credential access and privilege escalation techniques, specifically targeting the use of valid accounts to perform unauthorized actions.
Mitigation strategies for this vulnerability require immediate implementation of access control measures and system hardening practices. Organizations should disable or remove the vulnerable .htr files from the /iisadmpwd directory when they are not actively needed for administration tasks, or alternatively, implement proper authentication and authorization controls that prevent local users from directly accessing these handler files. The recommended approach involves configuring the IIS server to restrict access to the /iisadmpwd directory through proper permission settings, ensuring that only authorized administrators can access these sensitive components. Additionally, implementing network segmentation and limiting local user access to IIS servers can reduce the attack surface. From a compliance perspective, this vulnerability relates to CWE-284, which addresses improper access control, and aligns with security standards that require proper privilege separation and authentication controls. Organizations should also consider upgrading to newer versions of IIS that have addressed this specific vulnerability, as Microsoft released patches and updates to resolve these access control issues in subsequent releases. Regular security assessments and monitoring of IIS configurations should be conducted to ensure that similar vulnerabilities are not present in other administrative components of the web server infrastructure.