Matrix Synapse before 0.28.1 is prone to a denial of service flaw where malicious events injected with depth = 2^63 - 1 render rooms unusable, related to federation/federation_base.py and handlers/message.py, as exploited in the wild in April 2018.
{ "availability": "Available with Ubuntu Pro: https://ubuntu.com/pro", "ubuntu_priority": "medium", "binaries": [ { "binary_version": "0.24.0+dfsg-1ubuntu0.1~esm1", "binary_name": "matrix-synapse" } ] }