CVE-2026-50132: fallo de gravedad alta en budibase

Budibase is an open-source low-code platform. Prior to 3.39.0, `GET /api/chat-links/:instance/:token/handoff` is a public endpoint (no auth required) that performs a permanent, state-changing operation: it binds an external chat identity (Slack/Discord/MS Teams) to an authenticated Budibase user account, with no consent UI and no CSRF protection. The session token in the URL is created by the attacker (from their own /link slash command) and embeds the attacker's externalUserId. When an authenticated Budibase victim visits the URL, their account is silently and permanently linked to the attacker's Slack/Discord identity. The server responds with "Authentication succeeded." — no indication of what was linked. This vulnerability is fixed in 3.39.0.