CVE-1999-1316 is a vulnerability found in the Passfilt.dll component of Microsoft Windows NT Service Pack 2 (SP2), specifically affecting version 4.0 of the operating system. Passfilt.dll is responsible for enforcing password policies during user account creation and password changes. The vulnerability allows users to create passwords that contain their own username, which weakens the password strength significantly. This flaw undermines the intended security controls designed to prevent easily guessable passwords. Since the password can include the user's name, attackers can leverage this predictable pattern to perform more effective password guessing or brute-force attacks, increasing the likelihood of unauthorized access. The vulnerability has a CVSS v2 base score of 7.5, indicating a high severity level. The vector metrics (AV:N/AC:L/Au:N/C:P/I:P/A:P) show that the vulnerability is remotely exploitable over the network without authentication, with low attack complexity, and can impact confidentiality, integrity, and availability. Although no patch is available and no known exploits have been reported in the wild, the inherent weakness in password policy enforcement poses a significant risk, especially in environments still running legacy Windows NT 4.0 systems. The lack of patch availability means organizations must rely on compensating controls to mitigate the risk.

For European organizations, the impact of this vulnerability can be considerable, particularly for those still operating legacy Windows NT 4.0 systems in critical infrastructure, industrial control systems, or legacy enterprise environments. The ability for users to set weak passwords containing their usernames increases the risk of credential compromise through password guessing or brute-force attacks. This can lead to unauthorized access to sensitive systems and data, potentially resulting in data breaches, disruption of services, and loss of integrity of critical information. Given the vulnerability affects confidentiality, integrity, and availability, exploitation could facilitate lateral movement within networks, privilege escalation, and persistent access by attackers. Although Windows NT 4.0 is largely obsolete, some legacy systems in sectors such as manufacturing, utilities, or government may still be in use, making them vulnerable. The lack of patch availability further exacerbates the risk, requiring organizations to implement alternative security measures. Additionally, the vulnerability's remote exploitability without authentication means attackers can attempt to exploit it over the network, increasing the threat surface.

Since no official patch is available for this vulnerability, European organizations should implement the following specific mitigation strategies: 1) Identify and inventory all systems running Windows NT 4.0 and assess their criticality and exposure. 2) Where possible, upgrade or replace legacy Windows NT 4.0 systems with supported operating systems that enforce robust password policies. 3) If upgrading is not immediately feasible, implement network segmentation and strict access controls to isolate vulnerable systems from untrusted networks and limit exposure. 4) Enforce additional password complexity requirements through Group Policy or third-party tools that override or supplement Passfilt.dll behavior, preventing passwords containing usernames or other easily guessable patterns. 5) Deploy network-based intrusion detection and prevention systems (IDS/IPS) to monitor for suspicious login attempts or brute-force activity targeting legacy systems. 6) Conduct regular password audits and enforce periodic password changes to reduce the window of opportunity for attackers. 7) Educate users about the importance of strong passwords and the risks of using personal information in passwords. 8) Implement multi-factor authentication (MFA) where possible to add an additional layer of security beyond passwords. 9) Monitor logs and alerts for signs of unauthorized access attempts and respond promptly to incidents. These targeted measures will help mitigate the risk posed by the vulnerability in the absence of a patch.