A stack-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 corrupting a hyperloglog using the SETRANGE command, an attacker could cause Redis to perform controlled increments of up to 12 bytes past the end of a stack-allocated buffer.
A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).
The product writes data past the end, or before the beginning, of the intended buffer.