This indicates an attack attempt to exploit an IMAP Command Injection Vulnerability in RoundCube Webmail.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted request. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted request.
RoundCube Webmail 1.3.5 and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor: