This indicates an attack attempt to exploit a Code Injection Vulnerability in Sitecore XP.
The vulnerability is due to insufficient validation of user-supplied XML files. A remote attacker can exploit this vulnerability by sending a crafted request to the target system. Successful exploitation results in remote code execution.
Sitecore XP 7.5 Initial Release to 7.5 Update-2
Sitecore XP 8.0 Initial Release to 8.0 Update-7
Sitecore XP 8.1 Initial Release to 8.1 Update-3
Sitecore XP 8.2 Initial Release to 8.2 Update-7
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.