Netscape Communicator before version 4.73 and Navigator 4.07 do not properly validate SSL certificates, which allows remote attackers to steal information by redirecting traffic from a legitimate web server to their own malicious server, aka the "Acros-Suencksen SSL" vulnerability.
Netscape 4.73 and earlier follows symlinks when it imports a new certificate, which allows local users to overwrite files of the user importing the certificate.
Netscape Communicator 4.04 through 4.7 (and possibly other versions) in various UNIX operating systems converts the 0x8b character to a "<" sign, and the 0x9b character to a ">" sign, which could allow remote attackers to attack other clients via cross-site scripting (CSS) in CGI programs that do not filter these characters.
A configuration in a web browser such as Internet Explorer or Netscape Navigator allows execution of active content such as ActiveX, Java, Javascript, etc.