CVE-2006-1242

The ip_push_pending_frames function in Linux 2.4.x and 2.6.x before 2.6.16 increments the IP ID field when sending a RST after receiving unsolicited TCP SYN-ACK packets, which allows remote attackers to conduct an Idle Scan (nmap -sI) attack, which bypasses intended protections against such attacks.

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-1242