Hi, I have tested this on my qpopper 4.0.5 - and I get this response no matter from which host I test (even localhost): sun waldo # ./poptest mail.XXX.net gert Validating username gert , please stand by.. Disconnected after 119.993 seconds. User "gert" is probably a valid user But that user is not a valid user. I have APOP authentication on and required, thus the pop server responded with You must use TLS/SSL or stronger authentication such as APOP to connect to this server Maybe this is a temporary solution? Or maybe the issue was fixed in 4.0.5? Regards, - Waldo On Saturday 15 March 2003 21:13, Dennis Lubert wrote: > Hello, > > during development of a pop3 tool I found an issue that makes it possible > for any user to check the validity of a user on a target system. If a user > is valid and an invalid password has been supplied, then the system waits > ~10 seconds until it sends a disconnect message and disconnect. If the > username was not correct, then it disconnect immediately after the wrong > password. > > This makes it possible to scan a server for valid users, to generate spam > sending lists, or to check a username for another kind of attack. > > Tested against qpopper 3.1 and 4.0.4, others might be affected as well. > > Attached is the source code for a program that will do a simple check on a > pop3 server. Additionally qpopper will also return an answer if the > username supplied has a UID < 100 (< 10 for 3.1), which will also been > checked. > > The fix should be simple, there must be a usleep() call or similar that > should either be deleted, or added also to the part where the username was > not correct. > > greets > > Dennis
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