CVE-2021-21392

Description

Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. 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.

How to fix CVE-2021-21392

To remediate CVE-2021-21392, upgrade the affected package to a fixed version below.

• —upgrade to 1.28.0-1 or later
• —upgrade to 1.28.0rc1 or later
• —upgrade to 1.28.0 or later

Is CVE-2021-21392 being exploited?

Low — EPSS is 0.2%, meaning exploitation activity has not been observed at scale.

Affected packages (3)

• from 0, < 1.28.0-1
• from 0, < 1.28.0rc1
• from 0, < 1.28.0

CVSS scores

References (10)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2021-21392
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2021-21392
• PATCHgithub.com/matrix-org/synapse
• PATCHpypi.org/project/matrix-synapse/
• WEB