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.
Published 2021-03-26 20:15:12
Updated 2022-10-21 22:42:17
Source GitHub, Inc.
View at NVD,   CVE.org
Vulnerability category: Cross site scripting (XSS)

Exploit prediction scoring system (EPSS) score for CVE-2021-21333

0.11%
Probability of exploitation activity in the next 30 days EPSS Score History
~ 43 %
Percentile, the proportion of vulnerabilities that are scored at or less

CVSS scores for CVE-2021-21333

Base Score Base Severity CVSS Vector Exploitability Score Impact Score Score Source First Seen
2.6
LOW AV:N/AC:H/Au:N/C:N/I:P/A:N
4.9
2.9
NIST
6.1
MEDIUM CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N
1.6
4.0
NIST
6.1
MEDIUM CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N
1.6
4.0
GitHub, Inc.

CWE ids for CVE-2021-21333

References for CVE-2021-21333

Products affected by CVE-2021-21333

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