CVE-2000-0519 in Internet Explorer
Summary
by MITRE
Internet Explorer 4.x and 5.x does not properly re-validate an SSL certificate if the user establishes a new SSL session with the same server during the same Internet Explorer session, aka one of two different "SSL Certificate Validation" vulnerabilities.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 04/21/2026
The vulnerability described in CVE-2000-0519 represents a critical flaw in the secure socket layer certificate validation mechanism within Internet Explorer versions 4.x and 5.x. This issue stems from the browser's improper handling of SSL session resumption, where the security validation process fails to adequately verify certificates when establishing new connections to previously visited servers within the same browser session. The vulnerability specifically manifests when users navigate to websites that require SSL certificates, and the browser attempts to reuse cached session information while failing to perform proper certificate revalidation. This behavior creates a window of opportunity for attackers to exploit the trust relationship between the browser and web servers.
The technical implementation flaw lies in the browser's SSL state management system which does not enforce certificate validation checks during session resumption scenarios. When Internet Explorer encounters a new SSL session with a server that has been previously visited, the browser should perform complete certificate validation including checking certificate expiration dates, verifying certificate authorities, and ensuring the certificate matches the server's domain name. However, this validation process is bypassed or weakened in the resumption scenario, allowing potentially malicious certificates to be accepted without proper scrutiny. The vulnerability operates at the application layer of the OSI model and specifically affects the TLS/SSL handshake process within the browser's security subsystem. This flaw directly corresponds to CWE-295 which addresses improper certificate validation and CWE-310 which deals with cryptographic issues in SSL/TLS implementations.
The operational impact of this vulnerability is significant as it undermines the fundamental security guarantees provided by SSL/TLS encryption. Attackers can exploit this weakness to perform man-in-the-middle attacks by presenting forged certificates that would normally be rejected but are accepted due to the incomplete validation process. This allows unauthorized parties to intercept and potentially modify communications between users and web servers, compromising sensitive data including login credentials, personal information, and financial transactions. The vulnerability is particularly dangerous because it operates silently without alerting users to the security compromise, making detection extremely difficult. It affects all users who rely on Internet Explorer 4.x and 5.x for web browsing and creates a persistent security risk throughout the browser session, as long as the user maintains the same browser instance.
Organizations and users affected by this vulnerability should implement immediate mitigations including upgrading to newer versions of Internet Explorer that properly address this SSL validation flaw, disabling SSL session resumption features in the browser configuration, and implementing additional network-level security controls such as SSL inspection appliances. Security administrators should also consider deploying certificate pinning mechanisms and monitoring for suspicious certificate changes in network traffic. The vulnerability highlights the importance of proper certificate validation in cryptographic implementations and demonstrates how subtle flaws in security protocols can create substantial risks. From an ATT&CK framework perspective, this vulnerability maps to techniques involving credential access through man-in-the-middle attacks and privilege escalation via compromised trust relationships. Organizations should also consider implementing network segmentation and regular security assessments to identify and remediate similar vulnerabilities in their browser configurations and web infrastructure.