Vulnerability Instance

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.