CVE-2021-21392

published 2021-04-12

CVE-2021-21392: Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP…

Priority P4 32 medium 6.3 CVSS 3.1

AV N AC L PR L UI R S U C L I H A N

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.

Affected

4 ranges

Vendor	Product	Version range	Fixed in
debian	matrix-synapse	< matrix-synapse 1.28.0-1 (forky)	matrix-synapse 1.28.0-1 (forky)
fedoraproject	fedora	—	—
matrix-org	synapse	< 1.28.0	1.28.0
matrix	synapse	< 1.28.0	1.28.0

CVSS provenance

nvd v3.1 6.3 MEDIUM CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:H/A:N

nvd v2.0 4.9 MEDIUM AV:N/AC:M/Au:S/C:P/I:P/A:N

osv 6.3 MEDIUM

vendor_debian 6.3 MEDIUM

Stop checking back — get the weekly exploitation signal.

Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.

CWE-601