The detection rule for CVE-2018-15473 targets a known vulnerability in OpenSSH, specifically related to its handling of authentication requests. The exploit allows unauthorized users to enumerate valid usernames on the SSH daemon by leveraging a specific error message returned during the authentication process. This detection focuses on identifying exploitation attempts through monitoring error messages generated by the SSH daemon (sshd) on Linux systems. The primary keyword monitored is 'error: buffer_get_ret: trying to get more bytes 1907 than in buffer 308 [preauth]', which is indicative of attempts to exploit the vulnerability. Successfully detecting these keywords in logs can help flag potential reconnaissance activities where attackers strive to gather information about valid usernames on the targeted system.