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CVE-2021-21394— Denial of service (via resource exhaustion) due to improper input validation on third-party identifier endpoints

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 1.28.0版本之前存在安全漏洞，该漏洞源于Synapse缺少对端点上用于确认第三方标识符的某些参数的输入验证，可能会导致磁盘空间和内存的过度使用，从而导致资源耗尽。

CVSS 5.3 · Medium EPSS 1.54% · P75

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking
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I. Basic Information for CVE-2021-21394

Vulnerability Information
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Vulnerability Title
Denial of service (via resource exhaustion) due to improper input validation on third-party identifier endpoints
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 1.28.0 Synapse is missing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion. Note that the groups feature is not part of the Matrix specification and the chosen maximum lengths are arbitrary. Not all clients might abide by them. Refer to referenced GitHub security advisory for additional details including workarounds.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/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
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 1.28.0版本之前存在安全漏洞，该漏洞源于Synapse缺少对端点上用于确认第三方标识符的某些参数的输入验证，可能会导致磁盘空间和内存的过度使用，从而导致资源耗尽。
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 < 1.28.0 -

II. Public POCs for CVE-2021-21394

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III. Intelligence Information for CVE-2021-21394

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Patches & Fixes for CVE-2021-21394 (2)

Vendor Advisories for CVE-2021-21394 (1)

Mailing List Discussions for CVE-2021-21394 (1)

Other References for CVE-2021-21394 (1)

Same Patch Batch · matrix-org · 2021-04-12 · 3 CVEs total

CVE-2021-21392 6.3 MEDIUM Open redirect via transitional IPv6 addresses on dual-stack networks
CVE-2021-21393 5.3 MEDIUM Denial of service (via resource exhaustion) due to improper input validation on groups/com

IV. Related Vulnerabilities

Same product: synapse
Same vendor: matrix-org
Same weakness: CWE-20

V. Comments for CVE-2021-21394

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