CVE-2025-30355

Synapse vulnerable to federation denial of service via malformed events

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.

Category

7.1
CVSS
Severity: High
CVSS 3.1 •
EPSS 2.45% Top 20%
Affected: element-hq synapse
Published at:
Updated at:

References

Link Tags
https://github.com/element-hq/synapse/security/advisories/GHSA-v56r-hwv5-mxg6
https://github.com/element-hq/synapse/commit/2277df2a1eb685f85040ef98fa21d41aa4cdd389
https://github.com/element-hq/synapse/releases/tag/v1.127.1

Frequently Asked Questions

What is the severity of CVE-2025-30355?
CVE-2025-30355 has been scored as a high severity vulnerability.
How to fix CVE-2025-30355?
To fix CVE-2025-30355, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2025-30355 being actively exploited in the wild?
It is possible that CVE-2025-30355 is being exploited or will be exploited in a near future based on public information. According to its EPSS score, there is a ~2% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2025-30355?
CVE-2025-30355 affects element-hq synapse.
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