CVE-1999-1367 is a vulnerability affecting Microsoft Internet Explorer version 5.0, identified in 1999. The issue arises because Internet Explorer 5.0 does not properly reset the username and password cache for websites that do not implement standard cache control mechanisms. Specifically, when users visit web pages requiring authentication, Internet Explorer caches the credentials to facilitate seamless access. However, if the web server does not use standard HTTP cache control headers to prevent caching of sensitive authentication data, Internet Explorer fails to clear these cached credentials appropriately. This flaw can lead to a scenario where multiple users sharing the same system can access restricted web resources using cached credentials from previous sessions. The vulnerability primarily affects confidentiality and integrity, as unauthorized users on the same machine may gain access to protected web content without re-authentication. The CVSS score of 4.6 (medium severity) reflects that the attack vector is local (AV:L), requires low attack complexity (AC:L), no authentication (Au:N) is needed to exploit once local access is obtained, and impacts confidentiality, integrity, and availability to a partial degree (C:P/I:P/A:P). No patches are available, and no known exploits in the wild have been reported. Given the age of the vulnerability and the affected product version, this issue is largely historical but remains relevant in legacy environments where Internet Explorer 5.0 might still be in use.

For European organizations, the impact of this vulnerability is primarily relevant in environments where legacy systems and outdated browsers like Internet Explorer 5.0 are still operational. The vulnerability could allow unauthorized users sharing the same workstation to access sensitive web applications or intranet sites without proper authentication, leading to potential data leakage or unauthorized actions within restricted web portals. This risk is heightened in shared workstation scenarios such as public access terminals, call centers, or organizations with limited endpoint management. Although modern browsers and updated systems have long mitigated this issue, organizations with legacy infrastructure may face confidentiality breaches and potential compliance issues under data protection regulations like GDPR if sensitive personal or corporate data is exposed. The vulnerability does not facilitate remote exploitation, limiting its impact to local threat actors or insiders with physical or remote desktop access to the affected machine.

Given that no official patch is available for Internet Explorer 5.0, European organizations should prioritize the following mitigations: 1) Upgrade and migrate away from Internet Explorer 5.0 to modern, supported browsers that properly handle credential caching and adhere to current security standards. 2) Implement strict endpoint access controls and user session management to prevent unauthorized access to shared workstations, including enforcing user logoff and session timeouts. 3) Configure web servers to use appropriate cache control headers (e.g., 'Cache-Control: no-store, no-cache, must-revalidate') to prevent caching of authentication credentials on client browsers. 4) Employ endpoint security solutions that monitor and restrict credential caching behaviors or clear cached credentials upon session termination. 5) Educate users about the risks of shared workstation usage and encourage practices such as closing browsers and logging off after use. 6) For legacy systems that cannot be upgraded immediately, consider isolating them in secure network segments and restricting access to trusted personnel only.