What’s Vulnerable › Vulnerabilities

CVE-2023-32323: Synapse Outgoing federation to specific hosts can be disabled by sending malicious invites

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.0% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2023-05-26 · updated 2026-06-17
• Weakness: CWE-20

Description

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. A malicious user on a Synapse homeserver X with permission to create certain state events can disable outbound federation from X to an arbitrary homeserver Y. Synapse instances with federation disabled are not affected. In versions of Synapse up to and including 1.73, Synapse did not limit the size of `invite_room_state`, meaning that it was possible to create an arbitrarily large invite event. Synapse 1.74 refuses to create oversized `invite_room_state` fields. Server operators should upgrade to Synapse 1.74 or newer urgently.

Affected products

• matrix-org synapse: before 1.74.0 — fixed in 1.74.0

How to fix

Upgrade to a fixed version: matrix-org synapse 1.74.0. Check the vendor advisory for mitigations.

References

• https://github.com/matrix-org/synapse/issues/14492
• https://github.com/matrix-org/synapse/pull/14642
• https://github.com/matrix-org/synapse/security/advisories/GHSA-f3wc-3vxv-xmvr
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/UJIJRP5ZH6B3KGFLHCAKR2IX2Y4Z25QD/
• https://github.com/matrix-org/synapse/issues/14492
• https://github.com/matrix-org/synapse/pull/14642
• https://github.com/matrix-org/synapse/security/advisories/GHSA-f3wc-3vxv-xmvr
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/UJIJRP5ZH6B3KGFLHCAKR2IX2Y4Z25QD/

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