Shopify: mruby-engine: UAF in MRubyEngine#initialize enables local RCE

Summary Double-init of MRubyEngine frees engine + unmaps mspace, but leaves Ruby DATAPTR dangling. Kernel reuses freed VA via mmapMAPFIXED. Attacker forges memrubyengine struct + mrbstate in reclaimed region, points mrbstate-allocf at libc.system, arranges bytes of mrbstate to also spell a shell...

shopify-scripts: Crash: Overwriting NoMethodError with a builtin class crashes/corrupts memory

Uhm, while testing this I seem to have broken https://mruby.science.. Ooops, sorry about that! Anyway, here's the bug: Overwriting at least, not sure about other triggers NoMethodError with a builtin class like Fixnum or Integer leads to a rather interesting behavior. https://mruby.science didn't...