Bugzilla – Bug 1184754
VUL-0: CVE-2021-21392: matrix-synapse: IP blacklist bypass via transitional IPv6 addresses on dual-stack networks
Last modified: 2021-04-14 15:15:06 UTC
In Synapse before version 1.28.0 requests to user provided domains were not restricted to external IP addresses when transitional IPv6 addresses were used. Outbound requests to federation, identity servers, when calculating the key validity for third-party invite events, sending push notifications, and generating URL previews are affected. This could cause Synapse to make requests to internal infrastructure on dual-stack networks. See referenced GitHub security advisory for details and workarounds.