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CVE-2021-21273— Open redirects on some federation and push requests

Quick assessment

Affected
matrix-org synapse
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Matrix Synapse是英国Matrix基金会的一款矩阵管理服务器的实现。 Synapse 存在安全漏洞，该漏洞源于当计算第三方邀请事件的密钥有效性和发送推送通知时，对用户提供域的请求不受外部IP地址的限制。

CVSS 3.1 · Low EPSS 1.80% · P78

Possible ATT&CK Techniques 1 AI

T1557 · Adversary-in-the-Middle
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I. Basic Information for CVE-2021-21273

Vulnerability Information
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Vulnerability Title
Open redirects on some federation and push requests
Source: CVE Program / CVE List V5
Vulnerability Description
Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.25.0, requests to user provided domains were not restricted to external IP addresses when calculating the key validity for third-party invite events and sending push notifications. This could cause Synapse to make requests to internal infrastructure. The type of request was not controlled by the user, although limited modification of request bodies was possible. For the most thorough protection server administrators should remove the deprecated `federation_ip_range_blacklist` from their settings after upgrading to Synapse v1.25.0 which will result in Synapse using the improved default IP address restrictions. See the new `ip_range_blacklist` and `ip_range_whitelist` settings if more specific control is necessary.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
指向未可信站点的URL重定向(开放重定向)
Source: CVE Program / CVE List V5
Vulnerability Title
Matrix Synapse 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Matrix Synapse是英国Matrix基金会的一款矩阵管理服务器的实现。 Synapse 存在安全漏洞，该漏洞源于当计算第三方邀请事件的密钥有效性和发送推送通知时，对用户提供域的请求不受外部IP地址的限制。
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
matrix-org synapse < 1.25.0 -

II. Public POCs for CVE-2021-21273

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III. Intelligence Information for CVE-2021-21273

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Patches & Fixes for CVE-2021-21273 (2)

Vendor Advisories for CVE-2021-21273 (1)

Mailing List Discussions for CVE-2021-21273 (1)

Other References for CVE-2021-21273 (1)

IV. Related Vulnerabilities

Same product: synapse
Same vendor: matrix-org
Same weakness: CWE-601

V. Comments for CVE-2021-21273

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