This indicates an attack attempt against a Remote Code Execution vulnerability in the Advantech WebAccess.
The vulnerability is due to lack of validation for user supplied data when the vulnerable application handles a maliciously crafted request. An attacker can exploit this by uploading a malicious file and execute arbitrary code within the context of the affected application.
Advantech WebAccess 8.0 and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Currently we are unaware of any vendor supplied patch for this issue.