| Package | Affected versions | Patched versions |
|---|---|---|
| matrix-synapse | < 1.27.0 | 1.27.0 |
| synapse | < 1.27.0 | 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 issue is fixed in #9200.
For the missed messages notifications:
The notif.html, notif_mail.html, and room.html templates can be overridden with custom templates that manually escapes the variables using JInja2's escape filter. See the email.template_dir setting.
For the account expiry notifications:
Account expiry can be disabled via the account_validity.enabled setting.
The notice_expiry.html template can be overridden with a custom template that manually escapes the variables using JInja2's escape filter. See the email.template_dir setting.
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