BIND versions 9.11.0 through 9.16.50, 9.18.0 through 9.18.39, 9.20.0 through 9.20.13, 9.21.0 through 9.21.12, and their respective S1 variants are vulnerable to a cache poisoning issue. The vulnerability arises because BIND is too lenient when accepting records from DNS answers, which allows an attacker to inject forged data into the DNS cache.