QuickJS before 7414e5f has a quickjs.h JS_FreeValueRT use-after-free because of incorrect garbage collection of async functions with closures.
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.