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.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
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