Lettermint Node.js SDK leaks email properties to unintended recipients when client instance is reused

Impact

Email properties (such as to, subject, html, text, and attachments) are not reset between sends when a single client instance is reused across multiple .send() calls. This can cause properties from a previous send to leak into a subsequent one, potentially delivering content or recipient addresses to unintended parties. Applications sending emails to different recipients in sequence — such as transactional flows like password resets or notifications — are affected.

Patches

Yes, the issue has been patched. Users should upgrade to v1.5.1 or later.

Workarounds

If upgrading immediately is not possible, instantiate a new client for each send:

const client = new Lettermint({ apiKey: process.env.LETTERMINT_API_KEY });
await client.email.to('...').subject('...').html('...').send();

This ensures no state is carried over between sends.