The BIND resolver accepts validly-signed NSEC records where the Next Domain Name field points outside the signers zone. This issue affects BIND 9 versions 9.11.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23, 9.11.3-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.24-S1.
The product does not properly verify that the source of data or communication is valid.