This indicates an attack attempt to exploit an Arbitrary File Upload Vulnerability in Horde Groupware Webmailr.
The vulnerability is due to an error in the vulnerable application when handling File upload request. A remote authenticated attacker may be able to exploit this to upload arbitrary files and perform remote code execution within the context of the application, via uploading a malicious file.
Horde Groupware Webmail 5.2.22
Horde Groupware Webmail 5.2.17 with Horde Form version 2.0.10 and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor: