A heap-buffer overflow vulnerability was found in the Redis hyperloglog data structure versions 3.x before 3.2.13, 4.x before 4.0.14 and 5.x before 5.0.4. By carefully corrupting a hyperloglog using the SETRANGE command, an attacker could trick Redis interpretation of dense HLL encoding to write up to 3 bytes beyond the end of a heap-allocated buffer.