This indicates an attack attempt to exploit a Security Bypass vulnerability in SolarWinds Storage Manager.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the AuthenticationFilter module. A remote attacker may be able to exploit this to upload malicious files through bypassing the authentication filter.
SolarWinds Storage Manager 5.7.2 and prior
Security Bypass: Remote attackers can bypass security checks of vulnerable systems.
Apply the most recent upgrade or patch from the vendor