Synapse Outgoing federation to specific hosts can be disabled by sending malicious invites
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- None · None · Low
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| matrix-org | synapse | before 1.74.0 | 1.74.0 | Patch available | CNA |
| — | matrix-synapse (PyPI) | before 1.74.0 | 1.74.0 | Patch available | GHSA-f3wc-3vxv-xmvr |
- synapse Vendormatrix-org Affected before 1.74.0 Fixed in 1.74.0 Patch available CNA
- matrix-synapse (PyPI) Vendor— Affected before 1.74.0 Fixed in 1.74.0 Patch available GHSA-f3wc-3vxv-xmvr
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:* | before 1.74.0 | Vulnerable | matrix-org |
- cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:* Versions before 1.74.0 Vulnerable ·matrix-org
Remediation
- Fix · CNA synapse (matrix-org) Fixed in 1.74.0
- Fix · GHSA-f3wc-3vxv-xmvr matrix-synapse (PyPI) Fixed in 1.74.0 Advisory →
Vendor assessments
Timeline
- 2026-10-02 Threatist record created from CVE-2023-32323
- 2026-10-03 Alias added: GHSA-f3wc-3vxv-xmvr
References
Advisory 2
Other 4
- https://lists.fedoraproject.org/archives/list/[email protected]/message/UJIJRP5ZH6B3KGFLHCAKR2IX2Y4Z25QD/
- https://github.com/matrix-org/synapse
- https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2023-67.yaml
- https://lists.fedoraproject.org/archives/list/[email protected]/message/UJIJRP5ZH6B3KGFLHCAKR2IX2Y4Z25QD
More matrix-org Synapse vulnerabilities
- TI-2024-35327 Synapse allows a a malformed invite to break the invitee's `/sync` CVSS 4.0HIGH 8.7
- TI-2019-13571 Matrix Synapse before 1.5.0 mishandles signature checking on some federation APIs. CVSS 3.1CRITICAL 9.8
- TI-2024-36056 Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders CVSS 4.0HIGH 8.2
- TI-2024-35318 Synapse allows unsupported content types to lead to memory exhaustion CVSS 4.0HIGH 8.2
- TI-2018-11846 Matrix Synapse before 0.33.3.1 allows remote attackers to spoof events and possibly have… CVSS 3.0HIGH 8.8
- TI-2024-24814 Synapse denial of service through media disk space consumption CVSS 3.1HIGH 7.5
Sources
- CVE-2023-32323 · CVE Program
- CVE-2023-32323 · NVD
- FIRST EPSS
- GHSA-f3wc-3vxv-xmvr · GitHub Advisory Database · CC BY 4.0
- CVE-2023-32323 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences