matrix-synapse vulnerable to denial of service due to malicious server ACL events
Priority LOW 25CWE-770Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- High
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-770.
Summary
Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. Prior to version 1.94.0, a malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service. Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected. Server administrators are advised to upgrade to Synapse 1.94.0 or later. As a workaround, rooms with malicious server ACL events can be purged and blocked using the admin API.
Why it matters now
EPSS 0.01394 72nd percentileScored 2026-11-07
Fix Fixed synapse (matrix-org): 1.94.0matrix-synapse (PyPI): 1.94.0
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| matrix-org | synapse | before 1.94.0 | 1.94.0 | Patch available | CNA |
| — | matrix-synapse (PyPI) | before 1.94.0 | 1.94.0 | Patch available | GHSA-5chr-wjw5-3gq4 |
- synapse Vendormatrix-org Affected before 1.94.0 Fixed in 1.94.0 Patch available CNA
- matrix-synapse (PyPI) Vendor— Affected before 1.94.0 Fixed in 1.94.0 Patch available GHSA-5chr-wjw5-3gq4
CPE configurations NVD · 3
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:* | before 1.94.0 | Vulnerable | matrix-org |
| cpe:2.3:o:fedoraproject:fedora:37:*:*:*:*:*:*:* | 37 | Vulnerable | Fedoraproject |
| cpe:2.3:o:fedoraproject:fedora:38:*:*:*:*:*:*:* | 38 | Vulnerable | Fedoraproject |
- cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:* Versions before 1.94.0 Vulnerable ·matrix-org
- cpe:2.3:o:fedoraproject:fedora:37:*:*:*:*:*:*:* Versions 37 Vulnerable ·Fedoraproject
- cpe:2.3:o:fedoraproject:fedora:38:*:*:*:*:*:*:* Versions 38 Vulnerable ·Fedoraproject
Remediation
- Fix · CNA synapse (matrix-org) Fixed in 1.94.0
- Fix · GHSA-5chr-wjw5-3gq4 matrix-synapse (PyPI) Fixed in 1.94.0 Advisory →
Vendor assessments
Timeline
- 2026-10-02 Threatist record created from CVE-2023-45129
- 2026-10-03 Alias added: GHSA-5chr-wjw5-3gq4
References
Advisory 2
Other 11
- https://matrix-org.github.io/synapse/latest/admin_api/rooms.html#version-2-new-version
- https://lists.fedoraproject.org/archives/list/[email protected]/message/WRO4MPQ6HOXIUZM6RJP6VTCTMV7RD2T3/
- https://lists.fedoraproject.org/archives/list/[email protected]/message/KEVRB4MG5UXQ5RLZHSUJXM5GWEBYYS5B/
- https://lists.fedoraproject.org/archives/list/[email protected]/message/N6P4QULVUE254WI7XF2LWWOGHCYVFXFY/
- https://security.gentoo.org/glsa/202401-12
- https://github.com/matrix-org/synapse/commit/f84da3c32ec74cf054e2fd6d10618aa4997cffaa
- https://github.com/matrix-org/synapse
- https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2023-199.yaml
- https://lists.fedoraproject.org/archives/list/[email protected]/message/KEVRB4MG5UXQ5RLZHSUJXM5GWEBYYS5B
- https://lists.fedoraproject.org/archives/list/[email protected]/message/N6P4QULVUE254WI7XF2LWWOGHCYVFXFY
- https://lists.fedoraproject.org/archives/list/[email protected]/message/WRO4MPQ6HOXIUZM6RJP6VTCTMV7RD2T3
More matrix-org Synapse vulnerabilities
- TI-2023-15617 Synapse Outgoing federation to specific hosts can be disabled by sending malicious invites CVSS 3.1MEDIUM 5.0
- 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
Sources
- CVE-2023-45129 · CVE Program
- CVE-2023-45129 · NVD
- FIRST EPSS
- GHSA-5chr-wjw5-3gq4 · GitHub Advisory Database · CC BY 4.0
- CVE-2023-45129 · 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