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CVE-2021-21333— HTML injection in email and account expiry notifications

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。 Matrix Synapse 1.27.0 版本之前存在跨站脚本漏洞，该漏洞允许攻击者可利用该漏洞在电子邮件中插入伪造内容。

CVSS 6.1 · Medium EPSS 1.35% · P71
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I. Basic Information for CVE-2021-21333

Vulnerability Information
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Vulnerability Title
HTML injection in email and account expiry notifications
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 1.27.0, the notification emails sent for notifications for missed messages or for an expiring account are subject to HTML injection. In the case of the notification for missed messages, this could allow an attacker to insert forged content into the email. The account expiry feature is not enabled by default and the HTML injection is not controllable by an attacker. This is fixed in version 1.27.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
输出中的特殊元素转义处理不恰当(注入)
Source: CVE Program / CVE List V5
Vulnerability Title
Matrix Synapse 跨站脚本漏洞
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。 Matrix Synapse 1.27.0 版本之前存在跨站脚本漏洞，该漏洞允许攻击者可利用该漏洞在电子邮件中插入伪造内容。
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 < 1.27.0 -

II. Public POCs for CVE-2021-21333

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III. Intelligence Information for CVE-2021-21333

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Patches & Fixes for CVE-2021-21333 (2)

Vendor Advisories for CVE-2021-21333 (1)

Mailing List Discussions for CVE-2021-21333 (1)

Other References for CVE-2021-21333 (1)

IV. Related Vulnerabilities

Same product: synapse
Same vendor: matrix-org
Same weakness: CWE-74

V. Comments for CVE-2021-21333

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