This indicates an attack attempt to exploit a Buffer Overflow Vulnerability in Advantech WebAccess.
The vulnerability is due to an improper boundary check condition in the application. A remote, unauthenticated attacker can exploit this to execute arbitrary code, via a crafted request to the target system.
Advantech WebAccess prior to 8.4.2
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.