CVE-2021-34749

A vulnerability in Server Name Identification (SNI) request filtering of
Cisco Web Security Appliance (WSA), Cisco Firepower Threat Defense (FTD),
and the Snort detection engine could allow an unauthenticated, remote
attacker to bypass filtering technology on an affected device and
exfiltrate data from a compromised host. This vulnerability is due to
inadequate filtering of the SSL handshake. An attacker could exploit this
vulnerability by using data from the SSL client hello packet to communicate
with an external server. A successful exploit could allow the attacker to
execute a command-and-control attack on a compromised host and perform
additional data exfiltration attacks.