Affected: npm: axios

### Summary toFormData recursively walks nested objects with no depth limit, so a deeply nested value passed as request data crashes the Node.js process with a RangeError.

### Details lib/helpers/toFormData.js:210 defines an inner `build(value, path)` that recurses into every object/array child (line 225: `build(el, path ? path.concat(key) : [key])`). The only safeguard is a `stack` array used to detect circular references; there is no maximum depth and no try/catch around the recursion. Because `build` calls itself once per nesting level, a payload nested roughly 2000+ levels deep exhausts V8's call stack.

`toFormData` is the serializer behind `FormData` request bodies and `AxiosURLSearchParams` (used by `buildURL` when `params` is an object with `URLSearchParams` unavailable, see `lib/helpers/buildURL.js:53` and `lib/helpers/AxiosURLSearchParams.js:36`). Any server-side code that forwards a client-supplied object into `axios({ data, params })` therefore reaches the recursive walker with attacker-controlled depth.

The RangeError is thrown synchronously from inside `forEach`, escapes `toFormData`, and propagates out of the axios request call. In typical Express/Fastify request handlers this terminates the running request; in synchronous startup paths or worker threads it can crash the whole process.

### PoC ```js import toFormData from 'axios/lib/helpers/toFormData.js'; import FormData from 'form-data';

function nest(depth) { let o = { leaf: 1 }; for (let i = 0; i <…