How severe is CVE-2025-30355?

CVE-2025-30355 has a CVSS 3.x base score of 7.1, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability high.

Is CVE-2025-30355 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (63rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-30355?

CVE-2025-30355 affects Matrix Synapse. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2025-30355?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2025-30355 have an EU (EUVD) identifier?

Yes. CVE-2025-30355 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-8265.

When was CVE-2025-30355 published?

CVE-2025-30355 was published on 2025-03-27 and last updated on 2026-06-17.

CVE-2025-30355

CVE-2025-30355 is a high-severity vulnerability in Matrix Synapse with a CVSS 3.x base score of 7.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: High (CVSS 3.x base score 7.1)
EPSS exploit prediction: 1% (63rd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-8265
Weakness: CWE-20
Affected product: Matrix Synapse
Published: 2025-03-27
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2025-30355?: 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 severe is CVE-2025-30355?: CVE-2025-30355 has a CVSS 3.x base score of 7.1, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability high.
Is CVE-2025-30355 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (63rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-30355?: CVE-2025-30355 affects Matrix Synapse. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-30355?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2025-30355 have an EU (EUVD) identifier?: Yes. CVE-2025-30355 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-8265.
When was CVE-2025-30355 published?: CVE-2025-30355 was published on 2025-03-27 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*

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