High [CVE-2026-54592] Denial of Service via deeply nested JSON input

Oj (Optimized JSON) is a JSON parser and Object marshaller packaged as a Ruby gem. In versions prior to 3.17.3, Oj::Doc#each_child, when invoked recursively over a deeply nested JSON document, overflows a fixed-size stack buffer and aborts the process, leading to DoS.

In a two-step chain in ext/oj/fast.c, doc_each_child increments doc->where past the where_path[MAX_STACK = 100] array with no bounds check and never restores it (the doc->where-- is missing), so calling each_child recursively from inside the yield block drives doc->where beyond the array.

On the next entry the function copies the path into the 800-byte stack-local buffer save_path[MAX_STACK] using wlen = doc->where - doc->where_path, so when the previous recursive call left doc->where past where_path[100] the wlen exceeds MAX_STACK and the memcpy overflows save_path on the C stack; because the Oj::Doc parser imposes no JSON nesting-depth limit (relying on a C-stack pressure check), deeply nested attacker input reaches this path.

This issue has been fixed in version 3.17.3. A flaw was found in Oj, a Ruby gem for JSON parsing.

A remote attacker can exploit this vulnerability by providing a deeply nested JSON document. This can lead to a stack buffer overflow in the `Oj::Doc#each_child` function, causing the process to abort and resulting in a denial of service (DoS) for the affected system.