High severity · published Mar 27, 2025
CVE-2025-30355
Synapse vulnerable to federation denial of service via malformed events
7.5
CVSS
1.2%
EPSS
No
On KEV
Description
Synapse is an open source Matrix homeserver implementation. A malicious server can craft events which, when received, prevent Synapse version up to 1.127.0 from federating with other servers. The vulnerability has been exploited in the wild and has been fixed in Synapse v1.127.1. No known workarounds are available.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)1.2% · higher than 69% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
SY
synapse · element-hq
< 1.127.1 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-30355
CVE.org
https://www.cve.org/CVERecord?id=CVE-2025-30355
Patch
https://github.com/element-hq/synapse/commit/2277df2a1eb685f85040ef98fa21d41aa4cdd389
Release Notes
https://github.com/element-hq/synapse/releases/tag/v1.127.1
Vendor Advisory
https://github.com/element-hq/synapse/security/advisories/GHSA-v56r-hwv5-mxg6
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