CVE-1999-0387 is a vulnerability found in legacy Microsoft Windows operating systems, specifically Windows 95 and Windows 98. The issue stems from a credential caching mechanism that stores network passwords in plaintext. This design flaw allows an attacker with access to the affected system to retrieve these cached plaintext network passwords without requiring any authentication. The vulnerability is classified under CWE-255, which relates to the improper protection of credentials. The CVSS v2 score for this vulnerability is 7.8, indicating a high severity level, with the vector AV:N/AC:L/Au:N/C:C/I:N/A:N, meaning it can be exploited remotely over the network with low attack complexity, no authentication required, and results in a complete compromise of confidentiality, though integrity and availability remain unaffected. Although this vulnerability is quite old and affects obsolete operating systems, it remains relevant in environments where legacy systems are still in use. Microsoft issued a security bulletin (MS99-052) providing patches and mitigation guidance back in 1999. No known exploits have been reported in the wild, likely due to the obsolescence of the affected platforms. However, the plaintext storage of network passwords poses a significant risk if legacy systems are still connected to modern networks, as attackers could extract credentials and potentially pivot to other systems or escalate privileges within a network.

For European organizations, the primary impact of CVE-1999-0387 lies in the potential exposure of network credentials stored on legacy Windows 95 and Windows 98 systems. While these operating systems are largely obsolete and unsupported, some industrial control systems, embedded devices, or legacy business applications may still rely on them. If such systems are connected to corporate networks, attackers could leverage this vulnerability to harvest plaintext network passwords, leading to unauthorized access to network resources. This could compromise confidentiality and facilitate lateral movement within the network. Although integrity and availability are not directly impacted by this vulnerability, the exposure of credentials can indirectly lead to further attacks that affect these properties. European organizations with legacy infrastructure in sectors such as manufacturing, utilities, or government may be particularly at risk if these systems remain in use. The risk is compounded by the fact that these legacy systems often lack modern security controls and monitoring, making detection and response more difficult.

1. Immediate removal or isolation of Windows 95 and Windows 98 systems from corporate networks to prevent unauthorized access. 2. If legacy systems must remain operational, implement strict network segmentation and access controls to limit exposure. 3. Apply the official Microsoft patch MS99-052 if the systems are still maintained in any capacity. 4. Replace legacy systems with modern, supported operating systems wherever possible to eliminate the vulnerability entirely. 5. Conduct thorough credential audits and change any network passwords that may have been cached on legacy systems. 6. Implement network monitoring to detect unusual authentication attempts or lateral movement originating from legacy systems. 7. Educate IT staff about the risks of legacy systems and enforce policies to phase out unsupported operating systems. 8. Use multi-factor authentication and network-level encryption to reduce the impact of credential exposure.