Details for this vulnerability have not been published by NIST at this point. Descriptions from software vendor advisories for this issue are provided below.
USN-5332-1 fixed a vulnerability in Bind. This update provides the corresponding update for Ubuntu 14.04 ESM and Ubuntu 16.04 ESM.
Original advisory details:
Xiang Li, Baojun Liu, Chaoyi Lu, and Changgen Zou discovered that Bind incorrectly handled certain bogus NS records when using forwarders. A remote attacker could possibly use this issue to manipulate cache results. (CVE-2021-25220)