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RE: IIS SMTP component allows mail relaying via Null Session
From: "Toni Lassila" <toni.lassila () mc-europe com>
Date: Mon, 4 Mar 2002 08:13:03 +0200

-----Original Message-----
From: Todd Sabin [mailto:tsabin () razor bindview com]
Sent: Friday, March 01, 2002 17:31
To: bugtraq () securityfocus com
Subject: IIS SMTP component allows mail relaying via Null Session

Overview:
IIS comes with a small SMTP component.  The default settings allow
anyone who can authenticate to it to relay email.  Because the
authentication system supports NTLM, it is possible for anyone to
authenticate using null session credentials, and then relay email.

Workarounds:
Disable the SMTP service.
Disable the ability of authenticated users to relay email.
Firewall off the SMTP service from untrusted networks.

I suspect turning off NTLM authentication and allowing only Basic
Authentication (with or without TLS), or alternatively disabling
null session access (details are in many MS KB) from the server
are two possible workarounds as well. Disabling null sessions is
one of those security features one should do when securing a
Windows-based server anyway.

-- 
Toni Lassila         t.lassila () mc-europe com
Operations Engineer         +358 9 5655 1882

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