BunkerWeb: rDNS bypass via missing forward-confirmation (FCrDNS) in blacklist, greylist, and antibot

BunkerWeb is an open-source, next-generation Web Application Firewall. Prior to 1.6.13, the blacklist, greylist, and antibot modules in src/common/core/blacklist/blacklist.lua, src/common/core/greylist/greylist.lua, and src/common/core/antibot/antibot.lua trust PTR suffix matches in IGNORE_RDNS, GREYLIST_RDNS, and ANTIBOT_IGNORE_RDNS without using get_ips to confirm that the hostname resolves to the client address. An unauthenticated remote attacker who controls a PTR record can spoof a trusted suffix to bypass rDNS-based blacklisting, gain greylist treatment, or skip an antibot challenge. This issue is fixed in version 1.6.13.