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.
CVE-2021-21333
CVSS Score: 6.1 (MEDIUM)
EPSS Score: 0.11%
Risk Score: 4.27 (MEDIUM)
Risk Score based on CVSS score and EPSS. This score is for reference purposes and is not internationally recognized.
Mitre ATT&CK Technical v15.1
T1583.004 – Server
T1059.006 – Python
T1584.004 – Server
T1053.002 – At
Technical Analysis & Mitigation Measures
Reference Links
https://github.com/matrix-org/synapse/pull/9200
https://github.com/matrix-org/synapse/commit/e54746bdf7d5c831eabe4dcea76a7626f1de73df
https://github.com/matrix-org/synapse/releases/tag/v1.27.0
https://github.com/matrix-org/synapse/security/advisories/GHSA-c5f8-35qr-q4fm
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/
Vendor - Produce - Version
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