Directory Harvest Attacks

Directory Harvest Attacks (DHAs), sometimes called Dictionary Attacks, are carried out by spammers against mail servers. Various combinations of username are tried - a@example.com, b@example.com; if the server responds differently for a valid or invalid user, a list of valid users can be built up.

Various mail servers now have inbuilt protection against DHAs, and filtering gateways are available that can help.

Understanding Directory Harvest Attacks - www.pcmag.com/article2/0,1759,1543581,00.asp
What are Directory Harvest Attacks? - www.postini.com/services/what_are_dhas.html
See “Directory Harvest Attacks” at Postini Email Stat Track
Dictionary Attacks - mail.cotse.net/dictionary_attacks.html
Spammers Grab MSN Hotmail addresses - www.spamhaus.org/news.lasso?article=6

Application	Harvesting Advisories	Vulnerability Reference
Communigate	Communigate email verification email harvesting	CVE-2000-1002 BID-1792 XFDB-5363
Majordomo	Majordomo which_access variable set to “open” could disclose email addresses	BID-6761 XFDB-11243
Netscape Messaging	Netscape Messaging email verification email harvesting	CVE-2000-0960 BID-1787 XFDB-5364
NTMail	NTMail does not disable the VRFY command	CVE-1999-0819 BID-0856 XFDB-3719

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Page last updated: 11-Oct-2005