A penetration tester is assessing the security of a web application.

An HTTP 403 Forbidden response indicates the server understood the request but is refusing to authorize it. In PenTest+ web assessment context, a common cause is an access control requirement at the web server or reverse proxy layer—such as mutual TLS (mTLS) / client certificate authentication, IP allowlisting, or other authorization gates—preventing the tester from reaching the application content. When a site is configured to require a client certificate, the server may return a 403-class error if the request does not include a trusted certificate chain, because the client cannot be authenticated to an approved identity. Therefore, obtaining and presenting a valid X.509 client certificate (issued by a trusted CA for that environment or provided by the client as part of the engagement) is the appropriate step to satisfy the access requirement and proceed with testing.

Resetting server file permissions is an administrative remediation action outside a tester’s role and scope. Spoofing a server MAC address is not meaningful for HTTP access and typically not possible across routed networks. Using a legacy browser addresses client-side compatibility, not server-side authorization decisions that produce 403.