Synapse Denial of service due to incorrect application of event authorization rules during state resolution
Impact
If Synapse and a malicious homeserver are both joined to the same room, the malicious homeserver can trick Synapse into accepting previously rejected events into its view of the current state of that room. This can be exploited in a way that causes all further messages and state changes sent in that room from the vulnerable homeserver to be rejected.
Synapse homeservers are affected by this issue if and only if they are joined to rooms which members of untrusted homeservers are joined or invited to.
- Synapse homeservers in rooms available over public federation are affected.
- Synapse homeservers with federation disabled are not affected.
- Synapse homeservers in a closed federation containing only trusted servers are not affected.
- Synapse homeservers which are only joined to rooms with federation disabled[^1] are not affected.
Patches
Administrators of homeservers with federation enabled are advised to upgrade to 1.68.0 or higher.
Workarounds
- Federation can be disabled by setting
federation_domain_whitelistto an empty list ([]). from the vulnerable homeserver to be rejected. This issue has been patched in version 1.68.0
References
[^1]: See m.federate in the m.room.create definition.
For more information
If you have any questions or comments about this advisory, e-mail us at security@matrix.org.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | matrix-synapse | >= 1.62.0, < 1.68.0rc1 | 1.68.0rc1 |
References
- https://github.com/matrix-org/synapse/pull/13723
- https://github.com/matrix-org/synapse/security/advisories/GHSA-p9qp-c452-f9r7
- https://nvd.nist.gov/vuln/detail/CVE-2022-39374
- https://github.com/matrix-org/synapse/commit/b73cbb82157d9666e8d667733afebc0d09ed858c
- https://github.com/matrix-org/synapse
- https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2023-66.yaml
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/UJIJRP5ZH6B3KGFLHCAKR2IX2Y4Z25QD
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-400- Platform
- Python (PyPI)
- Package
matrix-synapse- Disclosed
- 24.05.2023
- Updated
- 11.10.2026 11:20
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2023-66 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-p9qp-c452-f9r7 - CC BY 4.0
Vulnerability history: matrix-synapse
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 45
- First → latest
- 03.2019 05.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 21
- Medium 21
- Low 3
Disclosures per year
- 2019: 3
- 2020: 3
- 2021: 12
- 2022: 7
- 2023: 9
- 2024: 7
- 2025: 2
- 2026: 2
-
Synapse Denial of service due to incorrect application of event authorization rules during state resolution this entry
Know which vulnerabilities affect your application
With the DockRay integration and software inventory enabled, DockRay checks reported component versions against known vulnerabilities and notifies you about confirmed matches. Coverage depends on the supported technology and available advisory data.