CVE-2000-0517 in Communicator
Summary
by MITRE
Netscape 4.73 and earlier does not properly warn users about a potentially invalid certificate if the user has previously accepted the certificate for a different web site, which could allow remote attackers to spoof a legitimate web site by compromising that site's DNS information.
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Analysis
by VulDB Data Team • 04/21/2026
The vulnerability described in CVE-2000-0517 represents a critical certificate validation flaw in Netscape Navigator 4.73 and earlier versions that fundamentally undermines the security of SSL/TLS communications. This issue stems from the browser's improper handling of certificate warnings when users have previously accepted a certificate for a different website, creating a dangerous trust model that can be exploited by attackers. The vulnerability operates at the core of public key infrastructure trust mechanisms, where the browser fails to properly alert users to potential certificate mismatches or security issues when a previously trusted certificate is reused across different domains or contexts.
The technical flaw manifests in the browser's certificate validation logic where it does not adequately distinguish between legitimate certificate reuse and malicious certificate substitution. When a user has previously accepted a certificate for one website, the browser maintains a trust state that can be exploited by attackers who compromise the DNS information of a legitimate website. This allows the attacker to present a certificate that was previously accepted for a different site, effectively bypassing the normal certificate validation warnings that should alert users to potential security threats. The vulnerability is particularly insidious because it leverages the user's existing trust relationship with a certificate authority or website, making the attack more convincing and harder to detect.
The operational impact of this vulnerability extends far beyond simple website spoofing, as it fundamentally compromises the integrity of the SSL/TLS security model that users rely upon for secure web communications. Attackers can exploit this weakness to perform man-in-the-middle attacks, redirect users to malicious sites, or steal sensitive information from unsuspecting users who believe they are communicating with legitimate websites. The vulnerability affects all users of Netscape 4.73 and earlier versions, creating a widespread security risk that could be exploited across numerous web applications and services. This flaw directly violates security principles outlined in the CWE-295 category for improper certificate validation and can be categorized under ATT&CK technique T1071.004 for application layer protocol traffic shaping.
This vulnerability demonstrates the critical importance of proper certificate validation and user warning mechanisms in web browsers. The flaw represents a failure in the certificate trust model implementation where the browser should have maintained separate trust contexts for different websites, even when the same certificate authority is involved. The attack vector relies on DNS compromise and certificate reuse, making it particularly dangerous in environments where DNS security is weak or where attackers can manipulate DNS records to redirect traffic to malicious servers. Organizations using affected Netscape versions should immediately implement mitigations including upgrading to newer browser versions, implementing additional security controls such as certificate pinning, and educating users about the risks of accepting certificates without proper validation. The vulnerability also highlights the need for comprehensive certificate management policies and the importance of proper security testing for SSL/TLS implementations in web browsers.