Activepieces: Cross-tenant file download via missing JWT audience check on step-files signed URL

Activepieces is an open source AI workflow automation platform. Prior to 0.83.0, the /v1/step-files/signed download endpoint verified the supplied JWT against the shared signing secret but did not check the token's audience, and combined with a missing null-check on the decoded fileId, this allowed any caller holding any valid Activepieces JWT (including a freshly created user's own access token) to receive a step-file belonging to another tenant. The file returned was whatever PostgreSQL happened to scan first for type = FLOW_STEP_FILE, varying over time as the database changed, so an authenticated user could obtain step-file attachments belonging to other tenants on the same instance; the attacker could not target a specific victim or file, and the access was read-only with no integrity or availability impact. This issue is fixed in version 0.83.0.