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.
External References: https://github.com/matrix-org/synapse/commit/e54746bdf7d5c831eabe4dcea76a7626f1de73df https://github.com/matrix-org/synapse/pull/9200 https://github.com/matrix-org/synapse/releases/tag/v1.27.0 https://github.com/matrix-org/synapse/security/advisories/GHSA-c5f8-35qr-q4fm
Created matrix-synapse tracking bugs for this issue: Affects: fedora-all [bug 1944139]
This CVE Bugzilla entry is for community support informational purposes only as it does not affect a package in a commercially supported Red Hat product. Refer to the dependent bugs for status of those individual community products.