Emails sent by pretix can utilize placeholders that will be filled with customer data. For example, when {name}
is used in an email template, it will be replaced with the buyer's
name for the final email. This mechanism contained two security-relevant
bugs:
-
It was possible to exfiltrate information about the pretix system through specially crafted placeholder names such as {{event.init.code.co_filename}}.
This way, an attacker with the ability to control email templates
(usually every user of the pretix backend) could retrieve sensitive
information from the system configuration, including even database
passwords or API keys. pretix does include mechanisms to prevent the usage of such
malicious placeholders, however due to a mistake in the code, they were
not fully effective for the email subject.
-
Placeholders in subjects and plain text bodies of emails were
wrongfully evaluated twice. Therefore, if the first evaluation of a
placeholder again contains a placeholder, this second placeholder was
rendered. This allows the rendering of placeholders controlled by the
ticket buyer, and therefore the exploitation of the first issue as a
ticket buyer. Luckily, the only buyer-controlled placeholder available
in pretix by default (that is not validated in a way that prevents the
issue) is {invoice_company}, which is very unusual (but not
impossible) to be contained in an email subject template. In addition
to broadening the attack surface of the first issue, this could
theoretically also leak information about an order to one of the
attendees within that order. However, we also consider this scenario
very unlikely under typical conditions.
Out of caution, we recommend that you rotate all passwords and API keys contained in your pretix.cfg https://docs.pretix.eu/self-hosting/config/ file.
Limit backend access to trusted users, do not use user-controlled variables in the email template subjects.