Editing Tunneling protocol (section)

=== Circumventing firewall policy ===
Users can also use tunneling to "sneak through" a firewall, using a protocol that the firewall would normally block, but "wrapped" inside a protocol that the firewall does not block, such as [[HTTP]].  If the firewall policy does not specifically exclude this kind of "wrapping", this trick can function to get around the intended firewall policy (or any set of interlocked firewall policies).

Another HTTP-based tunneling method uses the [[HTTP tunnel#HTTP CONNECT method|HTTP CONNECT method/command]]. A client issues the HTTP CONNECT command to an HTTP proxy.  The proxy then makes a TCP connection to a particular server:port, and relays data between that server:port and the client connection.<ref>{{cite web|url=http://www.ietf.org/rfc/rfc2817.txt|title=Upgrading to TLS Within HTTP/1.1|date=2000|work=RFC 2817|access-date=March 20, 2013}}</ref> Because this creates a security hole, CONNECT-capable HTTP proxies commonly restrict access to the CONNECT method.  The proxy allows connections only to specific ports, such as 443 for HTTPS.<ref>{{cite web|url=http://www.kb.cert.org/vuls/id/150227|title=Vulnerability Note VU#150227: HTTP proxy default configurations allow arbitrary TCP connections|date=2002-05-17|publisher=[[CERT Coordination Center|US-CERT]]|access-date=2007-05-10}}</ref>

Other tunneling methods able to bypass network firewalls make use of different protocols such as [[DNS]],<ref name="tunneling_dns">Raman, D., Sutter, B. D., Coppens, B., Volckaert, S., Bosschere, K. D., Danhieux, P., & Buggenhout, E. V. (2012, November). DNS tunneling for network penetration. In International Conference on Information Security and Cryptology (pp. 65-77). Springer, Berlin, Heidelberg.</ref> [[MQTT]],<ref name="tunneling_mqtt">Vaccari, I., Narteni, S., Aiello, M., Mongelli, M., & Cambiaso, E. (2021). Exploiting Internet of Things Protocols for Malicious Data Exfiltration Activities. IEEE Access, 9, 104261-104280.</ref> [[SMS]].<ref name="tunneling_sms">Narteni, S., Vaccari, I., Mongelli, M., Aiello, M., & Cambiaso, E. (2021). Evaluating the possibility to perpetrate tunnelling attacks exploiting shortmessage-service. Journal of Internet Services and Information Security, 11, 30-46.</ref>