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CVE-2021-21274— Denial of service attack via .well-known lookups

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 before version 1.25.0 存在安全漏洞，该漏洞源于恶意的homeserver会将请求重定向到一个大文件。这可能会导致拒绝服务攻击。

CVSS 4.3 · Medium EPSS 2.16% · P82

Possible ATT&CK Techniques 1 AI

T1498 · Network Denial of Service
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I. Basic Information for CVE-2021-21274

Vulnerability Information
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Vulnerability Title
Denial of service attack via .well-known lookups
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, a malicious homeserver could redirect requests to their .well-known file to a large file. This can lead to a denial of service attack where homeservers will consume significantly more resources when requesting the .well-known file of a malicious homeserver. This affects any server which accepts federation requests from untrusted servers. Issue is resolved in version 1.25.0. As a workaround the `federation_domain_whitelist` setting can be used to restrict the homeservers communicated with over federation.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5
Vulnerability Title
Matrix Synapse 资源管理错误漏洞
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 before version 1.25.0 存在安全漏洞，该漏洞源于恶意的homeserver会将请求重定向到一个大文件。这可能会导致拒绝服务攻击。
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 >=0.99.0, < 1.25.0 -

II. Public POCs for CVE-2021-21274

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III. Intelligence Information for CVE-2021-21274

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Patches & Fixes for CVE-2021-21274 (2)

Vendor Advisories for CVE-2021-21274 (1)

Mailing List Discussions for CVE-2021-21274 (1)

Other References for CVE-2021-21274 (1)

IV. Related Vulnerabilities

Same product: synapse
Same vendor: matrix-org
Same weakness: CWE-400

V. Comments for CVE-2021-21274

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