CVE-1999-0755 is a vulnerability affecting Windows NT Remote Access Service (RAS) and Routing and Remote Access Service (RRAS) clients, specifically in Windows 2000 version 4.0. The issue arises because these clients cache a user's password even if the user has not explicitly selected the "Save password" option during connection setup. This behavior leads to unintended storage of sensitive authentication credentials on the client system. The vulnerability is classified under CWE-255, which relates to credentials management weaknesses. The CVSS v2 base score is 5.0 (medium severity), with the vector AV:N/AC:L/Au:N/C:P/I:N/A:N, indicating that the vulnerability can be exploited remotely without authentication, requires low attack complexity, and impacts confidentiality by exposing user passwords, but does not affect integrity or availability. Although no known exploits have been reported in the wild, the risk lies in potential unauthorized access to cached credentials, which could be extracted by local attackers or malware to impersonate users or escalate privileges. A patch addressing this issue is available from Microsoft as per security bulletin MS99-017. The vulnerability is historical but remains relevant for legacy systems still running Windows 2000 or NT RRAS/RAS clients. Organizations using these outdated systems may be unknowingly exposing user credentials due to this caching behavior.

For European organizations, the impact of CVE-1999-0755 primarily concerns confidentiality breaches. If an attacker gains local access to a system with cached passwords, they could extract these credentials and use them to access network resources or escalate privileges, potentially leading to further compromise. Although the vulnerability does not directly allow remote exploitation without authentication, the presence of cached passwords increases the risk surface, especially in environments where endpoint security is weak or where insider threats exist. Organizations relying on legacy Windows 2000 systems or RRAS/RAS clients for remote access may face increased risk of credential theft, which could undermine trust in remote access mechanisms and lead to unauthorized data access. Given the age of the vulnerability, modern systems are unlikely to be affected, but sectors with legacy infrastructure—such as industrial control systems, government agencies, or critical infrastructure operators—may still be vulnerable. The confidentiality impact could cascade into broader security incidents if attackers leverage stolen credentials to move laterally within networks.

To mitigate CVE-1999-0755, European organizations should prioritize the following actions: 1) Apply the official Microsoft patch from security bulletin MS99-017 immediately to affected Windows 2000 and NT RRAS/RAS clients to eliminate the password caching behavior. 2) Conduct an inventory of legacy systems to identify any devices still running Windows 2000 or earlier RRAS/RAS clients and plan for their upgrade or decommissioning, as these systems are no longer supported and pose ongoing security risks. 3) Implement endpoint security controls to restrict local access and prevent unauthorized extraction of cached credentials, including the use of disk encryption and strong access controls. 4) Educate users about the risks of password caching and enforce policies that discourage saving passwords on remote access clients. 5) Monitor network and endpoint logs for unusual authentication attempts or lateral movement that could indicate misuse of stolen credentials. 6) Where possible, replace legacy remote access solutions with modern, secure VPN technologies that do not cache passwords insecurely and support multifactor authentication.