CVE-2025-30355
Synapse vulnerable to federation denial of service via malformed events
7.1
HIGH
CVSS 3.1
EPSS 1.2%
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.
How to fix CVE-2025-30355
To remediate CVE-2025-30355, upgrade the affected package to a fixed version below.
- —upgrade to 1.127.1 or later
- —upgrade to 1.127.1 or later
Is CVE-2025-30355 being exploited?
Low — EPSS is 1.2%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0, < 1.127.1
- from 0, < 1.127.1
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH7.1 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H |