NSClient++ 0.5.2.35 Local Privilege Escalation via ExternalScripts and Web Interface

Summary

A local privilege escalation vulnerability exists in NSClient++ 0.5.2.35 when both the web interface and ExternalScripts features are enabled. The configuration file (nsclient.ini) stores the administrative password in plaintext and is readable by local users. By extracting this password, an attacker can authenticate to the NSClient++ web interface (typically accessible on port 8443) and abuse the ExternalScripts plugin to inject and execute arbitrary commands as SYSTEM by registering a custom script, saving the configuration, and triggering it via the API. This behavior is documented but insecure, as the plaintext credential exposure undermines access isolation between local users and administrative functions.