n8n before 1.123.73 Local File Read and SSRF via Gmail and Brevo nodes

n8n versions before 1.123.73, 2.35.4, and 2.36.2 pass message content in the Gmail (v1) and Brevo nodes to the mail composer without verifying it is a string. An authenticated user able to run a workflow can supply an expression that resolves to an object carrying a path or href property, causing the composer to read a local file accessible to the n8n process or fetch an internal URL (SSRF) and attach the result to the outgoing message.