Affected: npm: nodemailer

## Submission metadata

| Field | Value | |---|---| | Ecosystem | npm | | Package | `nodemailer` | | Repository | https://github.com/nodemailer/nodemailer | | Tested commit | `40d52215aac65b811d7e131bc916f68605efd9d2` | | Current tested version | `10.0.1` | | Confirmed vulnerable versions | `2.7.2`, `3.0.0`, `7.0.11`, `9.1.1`, `10.0.1` | | Proposed affected range | `>= 2.7.2, <= 10.0.1` | | Patched version | 10.0.2 |

## Summary

Nodemailer 10.0.1 does not safely process deeply nested arrays supplied through recipient fields such as `to`, `cc`, and `bcc`.

The public `MimeNodeAddressInput` type recursively permits arrays, but `MimeNode._parseAddresses()` flattens only the outermost array. A remaining nested array is passed to `addressparser()`, whose `Tokenizer` coerces the input with `.toString()`. Native `Array.prototype.toString()` recursively processes every nested array through `join()` and `toString()` until the V8 call stack is exhausted.

A valid 10,021-byte JSON recipient value containing one address wrapped in 5,000 arrays causes:

```text RangeError: Maximum call stack size exceeded ```

The exception occurs through the normal `sendMail()` API before the `maxRecipients` limit is evaluated. If the integrating application does not catch the synchronous exception around the complete `sendMail()` invocation, the Node.js worker or server process terminates.

No SMTP server, remote host, large attachment, or successful email delivery is required.

This is distinct from…