FreeBSD: VID-38d2df4d-b143-11e9-87e7-901b0e934d69: py-matrix-synapse -- multiple vulnerabilities

Matrix developers report: The matrix team releases Synapse 1.2.1 as a critical security update. It contains patches relating to redactions and event federation: Prevent an attack where a federated server could send redactions for arbitrary events in v1 and v2 rooms. Prevent a denial-of-service attack where cycles of redaction events would make Synapse spin infinitely. Prevent an attack where users could be joined or parted from public rooms without their consent. Fix a vulnerability where a federated server could spoof read-receipts from users on other servers. It was possible for a room moderator to send a redaction for an m.room.create event, which would downgrade the room to version 1.