Mako

Exploiting SSTI Vulnerability in Messenger Machine on Standoff 365 Leads to RCE and Corporate Chat Access

A detailed writeup published by Positive Technologies researcher Seven11eleven demonstrates a full attack chain against the vulnerable Messenger machine on the Standoff 365 platform. The researcher began with network reconnaissance using nmap and directory fuzzing with ffuf, uncovering Swagger documentation and JWT-protected endpoints. After identifying user enumeration through the friend search feature, the team discovered a Server-Side Template Injection flaw in the friendship summary functionality powered by the Mako template engine. The SSTI was escalated to remote code execution by injecting Python expressions that leveraged the self.module.cache.util chain to call os.popen commands. With initial access obtained via reverse shell, the attacker pivoted to neighboring services including Gitness, RabbitMQ, and Redis to achieve the defined business risks of accessing developer corporate messaging and extracting the city messenger encryption key.