The args array passed into the sandbox carried the host realm prototype
chain, so a script could reach the host Function constructor via
args.constructor.constructor and execute arbitrary code in the host
process (read files, run shell commands, dump env vars).
Construct args inside the sandbox context using vm.runInContext('[]'),
then populate with string primitives. The resulting array's prototype
chain belongs to the sandbox realm, so constructor traversal cannot
escape. Strings are primitives and safe to cross the realm boundary.
Affects use_sandbox=true path only. The use_sandbox=false path
(invokeFunction) is intentionally left as-is and explicitly marked as
dangerous-by-design — it compiles and runs user-supplied scripts in
the host realm via vm.compileFunction (parsingContext only isolates
parsing, not execution). It remains as a documented performance
trade-off for trusted, non-public clusters; a startup WARN is logged
when script.use_sandbox=false, and an operator-facing yaml comment
sits next to the setting in config/default.yml.
Reported by Hiroki Imai, LAC Co., Ltd.
Sergey Matvienko
e5734208e9