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 and managed services 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: 17-Oct-2009