CVE-2025-30355: Synapse vulnerable to federation denial of service via malformed events
- Is it exploited?
Reported, not confirmed by CISA. VulnCheck KEV lists it as exploited in the wild. CISA has not added it to its Known Exploited Vulnerabilities catalog as of .
VulnCheck KEV lists it since . It cites 4 public reports, the first from .
- How likely is exploitation in the next 30 days?
- 1.2%
EPSS score, percentile 68.8 of all scored records. A probability estimated by FIRST, not a report of exploitation.
- How severe?
- 7.1 High
CVSS v3.1 base score, given by the CNA
- What should I do?
CISA has set no required action, because the vulnerability is not in KEV.
The CVE record links no vendor advisory, patch or mitigation.
- Which versions are affected?
Affected
- < 1.127.1
Source: CISA KEV 2026.10.29, as of ; VulnCheck KEV, as of ; FIRST EPSS, as of ; CVE List, as of . About the data.
Description
Synapse vulnerable to federation denial of service via malformed events
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.
Source: CVE List, as of . About the data.
What to do
Advisories and patches
The CVE record links no vendor advisory, patch or mitigation.
This summary is based on the CVE record as of . Check the vendor's advisory before you act: affected versions and fixes can change.
Affected products and versions
Versions by product, as listed in the CVE record (1 product)
| Status | Versions |
|---|---|
| Affected | < 1.127.1 |
Source: CVE List, as of . About the data.
Weakness
CWE-20
- CWE-20: Improper Input Validation
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record.
Timeline
| Date | Event |
|---|---|
| CVE record published |