An issue in Hikvision DS-2CD1321-I V5.7.21 build 230819 allows attackers to cause a Denial of Service (DoS) via sending a crafted POST request to the endpoint /ISAPI/Security/challenge. The vendor has stated that upgrading to V5.7.23_SP2 fixes the issue.
https://www.hikvision.com/en/support/download/firmware/
https://crashpark.weebly.com/blog/hikvision-ip-camera-unauthenticated-denial-of-service-dos