An issue was discovered in Pulse Secure Pulse Connect Secure (PCS) through 2020-04-06. The applet in tncc.jar, executed on macOS, Linux, and Solaris clients when a Host Checker policy is enforced, launches a TCP server that accepts local connections on a random port. This can be reached by local HTTP clients, because up to 25 invalid lines are ignored, and because DNS rebinding can occur. (This server accepts, for example, a setcookie command that might be relevant to CVE-2020-11581 exploitation.)