Sandbox Breakout Affecting realms-shim package, versions <1.2.0

realms-shim is a shim implementation of the Realm API Proposal.

Affected versions of this package are vulnerable to {{ affectedlibrary.vulnerability.title }}, which would allow the attacker to run arbitrary code.

The vulnerable paths:

1. Reflect.construct can be used on the sandboxed Function constructor to reach the prototypes of the primal Realm.
2. The package's confined evaluator depended upon correct behavior of the spread operator a = [...b, ...c], which could be modified by the confined code.
3. The package has an uncaught exception that may allow an attacker to break out of the sandbox by catching the exception and using the caught Exception object.
4. The package's core evaluator, which must switch between "unsafe mode" and "safe mode" for each call, could be left in "unsafe mode" if an attacker is able to force a RangeError in a specific timeframe.

• GitHub Advisory

• NPM Security Advisory #1

• NPM Security Advisory #2

• NPM Security Advisory #3

• NPM Security Advisory #4