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CVE-2021-21333

nvd nist
Published: Mar 26, 2021Modified: Jun 17, 2026

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6.1
Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N
Exploitability: 1.6 / Impact: 4.0
Source: NVD

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.

Affected (2)

Matrix
1 product
Synapse
Fedoraproject
1 product
Fedora
Configuration A
1 vulnerable
Vulnerable SoftwareAffected Versions
Synapse
Before 1.27.0
Configuration B
1 vulnerable
Vulnerable SoftwareAffected Versions
Fedora
Version 34

Related CWEs

CWE-74
Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.
CWE-79
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

References (10)

Source: security-advisories@github.com
PatchThird Party Advisory
Source: security-advisories@github.com
PatchThird Party Advisory
Source: security-advisories@github.com
Third Party Advisory
Source: security-advisories@github.com
PatchThird Party Advisory
Source: security-advisories@github.com
Source: af854a3a-2127-422b-91ae-364da2661108
PatchThird Party Advisory
Source: af854a3a-2127-422b-91ae-364da2661108
PatchThird Party Advisory
Source: af854a3a-2127-422b-91ae-364da2661108
Third Party Advisory
Source: af854a3a-2127-422b-91ae-364da2661108
PatchThird Party Advisory
Source: af854a3a-2127-422b-91ae-364da2661108

Timeline

No history available yet.