The issue allows authorized users to cause a denial of service attack by sending re-INVITE with SDP containing duplicate codec names. When a call completes codec negotiation, the `codec string` channel variable is set with the result of the negotiation. On a subsequent re-negotiation, if an SDP is offered that contains codecs with the same names but with different formats, there may be too many codec matches detected by FreeSWITCH leading to overflows of its internal arrays. By abusing this vulnerability, an attacker is able to corrupt the stack of FreeSWITCH leading to an undefined behavior of the system or simply crash it.