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> Chapter 33 - VoIP Solutions: SIP > Deep SIP message inspection

Deep SIP message inspection

Deep SIP message syntax inspection (also called Deep SIP header inspection or SIP fuzzing protection) provides protection against malicious SIP messages by applying SIP header and SDP profile syntax checking. SIP Fuzzing attacks can be used by attackers to discover and exploit vulnerabilities of a SIP entity (for example a SIP proxy server). Most often these attacks could crash or compromise the SIP entity.

Deep SIP message inspection

Deep SIP message inspection checks the syntax of each SIP header and SDP profile line to make sure they conform to the syntax defined in the relevant RFC and IETF standard. You can also configure the SIP ALG to inspect for:

  • Unknown SIP message types (message types not defined in a SIP RFC) this option is enabled by default and can be disabled. When enabled unknown message types are discarded. Configured using the block-unknown option.
  • Unknown line types (message line types that are not defined in any SIP or SDP RFC). Configured using the unknown-header option.
  • Messages that are longer than a configured maximum size. Configured using the max‑body-length option.
  • Messages that contain one or more lines that are longer that a set maximum line length (default 998 characters). Configured using the max-line-length option.