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CVE-2025-30355— Synapse vulnerable to federation denial of service via malformed events

Quick assessment

Affected
element-hq synapse
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Element Synapse是Element开源的一个开源 Matrix 家庭服务器实现。 Element Synapse 1.127.0及之前版本存在输入验证错误漏洞，该漏洞源于恶意服务器可阻止与其他服务器联合。

CVSS 7.1 · High EPSS 1.20% · P67

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service
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I. Basic Information for CVE-2025-30355

Vulnerability Information
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Vulnerability Title
Synapse vulnerable to federation denial of service via malformed events
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
输入验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Element Synapse 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Element Synapse是Element开源的一个开源 Matrix 家庭服务器实现。 Element Synapse 1.127.0及之前版本存在输入验证错误漏洞，该漏洞源于恶意服务器可阻止与其他服务器联合。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
element-hq synapse < 1.127.1 -

II. Public POCs for CVE-2025-30355

# POC Description Source Link Shenlong Link
1 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. https://github.com/ui-bootstrap/CVE-2025-30355 POC Details
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Qwen3.6-35B-A3B · 7611 chars
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III. Intelligence Information for CVE-2025-30355

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Patches & Fixes for CVE-2025-30355 (1)

Vendor Advisories for CVE-2025-30355 (1)

Vendor Pages for CVE-2025-30355 (1)

IV. Related Vulnerabilities

Same product: synapse
Same vendor: element-hq
Same weakness: CWE-20

V. Comments for CVE-2025-30355

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