source: https://www.securityfocus.com/bid/7967/info

Multiple buffer overrun vulnerabilities have been discovered in Kerio MailServer, which affect the webmail component. The problem occurs when handling usernames of excessive length and likely occurs due to insufficient bounds checking. Due to the similarity of these issues it has been conjectured that the root of the problem may be a single function used to handle all affected procedures.

Successful exploitation of this vulnerability could potentially result in the execution of arbitrary code, with the privileges of the Kerio MailServer process.

http://[server]/do_subscribe?showuser=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAA