In versions of mruby up to and including 1.4.0, an integer overflow exists in src/vm.c::mrb_vm_exec() when handling OP_GETUPVAR in the presence of deep scope nesting, resulting in a use-after-free. An attacker that can cause Ruby code to be run can use this to possibly execute arbitrary code.
https://lists.debian.org/debian-lts-announce/2022/05/msg00006.html
https://github.com/mruby/mruby/issues/3995
https://github.com/mruby/mruby/commit/1905091634a6a2925c911484434448e568330626