Oj (Optimized JSON) is a JSON parser and Object marshaller packaged as a Ruby gem. In versions prior to 3.17.2, when in usual mode with createid enabled, Oj::Parser#parse is vulnerable to heap corruption via a negative-size memcpy. When a JSON object key is exactly 65,535 bytes long, an integer truncation in formattr (usual.c:63) converts the length to -1 before passing it to memcpy. This causes memcpy to copy SIZEMAX bytes (interpreted as a huge sizet), corrupting heap memory and crashing the process. The issue has been fixed in version 3.17.2.