During Spring 2022, a company discovered that one of their equipments was communicating with a known command and control server. As a result, the company decided to contact CERT Intrinsec in order to get help to handle the security breach and manage the crisis. CERT Intrinsec gathered information about malicious activities that were discovered on victim’s information system, and past incidents. Our in-depth analysis led us to conclude that an advanced persistent threat dubbed APT27 (a.k.a LuckyMouse, EmissaryPanda) actually compromised the company’s internal network for more than a year by exploiting a public facing application. Our analysis showed that the threat actor managed to compromise five different domains and to gain persistence on many equipments while trying to hide in plain sight. Besides, APT27 operators collected technical and business-related informations and exfiltrate almost three terabytes of data. As investigations went on, we observed tactics, techniques and procedures that had already been documented in papers, but we discovered new ones as well. CERT Intrinsec wanted to share with the community fresh and actionnable threat-intelligence related to APT27. That is why this report presents a timeline of actions taken by the attackers and the tactics, techniques and procedures seen during our incident response. It provides as well a MITRE ATT&CK diagram and several recommendations to follow if you came across such incident, and to prevent them.