Sendmail (till the latest version) Denial of Service.
29 Oct. 1998
Summary
Sendmail seems to be vulnerable to a Denial of Service where by connecting to the server and immediately disconnected, Sendmail would go into a 5 seconds "sleep mode".
There seems to be a "feature" in the code of Sendmail (/src/daemon.c) where when a server gets an error while trying to run the function accept(), it will refuse connections for about 5 seconds (There is a 'sleep' command inside the a 'if' clause that is entered when accept() returns a value that differs than 0).
To cause a DoS from this is quite easy, and by following the attached "algorithm" one could cause Sendmail to complete refuse connections:
1) Send a SYN packet to destination port 25.
2) Send a RST packet to destination port 25.
3) Wait a few seconds (approximately 2 seconds)
4) Redo line (1).
The vulnerability was found by Michal Zalewski lcamtuf@IDS.PL.
