vm2: sandbox boundary bypass via host Promise resolution preserving host object identity

vm2 is an open source vm/sandbox for Node.js. Prior to 3.11.0, a sandbox boundary violation in vm2 allows host object identity to cross into the sandbox through host Promise resolution. When a host-side Promise that resolves to a host object is exposed to the sandbox, the value delivered to the sandbox .then() callback preserves host identity. This allows the sandbox to interact with the host object directly, including performing identity checks using host-side WeakMap and mutating host object state from inside the sandbox. This behavior occurs because the Promise fulfillment wrapper uses ensureThis() instead of the stronger cross-realm conversion path (from() / proxy wrapping). If no prototype mapping is found, ensureThis() returns the original object. As a result, objects resolved by host Promises can cross the sandbox boundary without proper isolation. This vulnerability is fixed in 3.11.0.

Source published

13 May 2026 17:23:35 UTC

Source modified

13 May 2026 18:20:55 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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CVSS 3.1 · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N