GHSA-r7g4-qg5f-qqm2: Nodemailer: Improper TLS Certificate Validation in OAuth2 Token Fetch Enables Credential Interception

Nodemailer disables TLS certificate verification in its internal HTTPS fetch client through the use of rejectUnauthorized: false inside lib/fetch/index.js.

As a result, OAuth2 token requests trust invalid or self-signed HTTPS certificates and transmit sensitive OAuth credentials over connections that should fail TLS validation.

An attacker in a machine-in-the-middle position can intercept OAuth2 credential exchanges and capture:

• OAuth client_secret
• refresh_token
• access tokens

The issue was verified through runtime testing using a self-signed HTTPS OAuth endpoint.