Microsoft Exchange Server Lets Remote Users Send or Relay Unauthorized Mail (including SPAM) Via the Server
SecurityTracker Alert ID: 1003685|
SecurityTracker URL: http://securitytracker.com/id/1003685
(Links to External Site)
Updated: Apr 16 2004|
Original Entry Date: Feb 28 2002
Host/resource access via network|
Fix Available: Yes Vendor Confirmed: Yes |
Microsoft issued a security bulletin (MS02-11) warning of a vulnerability in the Windows 2000 SMTP service and in Exchange Server 5.5. A remote user could relay unauthorized mail via the system.|
It is reported that the SMTP service that is part of the Internet Mail Connector (IMC) for Microsoft Exchange Server 5.5, sometimes also also known as the Microsoft Exchange Internet Mail Service, contains a vulnerability in the processing of valid responses from the NTLM authentication layer of the underlying operating system.
The Exchange Server 5.5 IMC, upon receiving notification from the NTLM authentication layer that a user has been authenticated, reportedly fail to perform the required additional checks before granting the user access to the service. In most cases, a remote user that can successfully authenticate to the server can gain access to the SMTP service.
Microsoft reports that Exchange 2000 servers are not affected.
Microsoft has assigned this vulnerability a maximum severity rating of "Low".
A remote user that can successfully authenticate to the server can gain access to the SMTP service and, for example, send or relay mail via the server.|
The vendor has issued a fix. In April 2004, the vendor added a fix for Windows NT 4.0. Shown below is the fix for Exchange, as well the fixes for Windows 2000 and NT 4.0 which are affected by the same vulnerability [a separate Alert has been issued regarding the Windows 2000 and NT 4.0].|
Windows 2000 Server, Professional and Advanced Server:
Windows NT Server 4.0:
Exchange Server 5.5:
Windows 2000 Datacenter Server:
Patches for Windows 2000 Datacenter Server are hardware-specific and available from the original equipment manufacturer, the vendor said.
The Windows 2000 patch can be installed on Windows 2000 SP1, the Windows NT Server 4.0 patch can be installed on Windows NT Server 4.0 SP6a, and the Exchange Server 5.5 patch can be installed on Exchange Server 5.5 SP4.
This fix will be included in Windows 2000 SP3.
A reboot is required after installing this patch.
Vendor URL: www.microsoft.com/technet/security/bulletin/MS02-011.asp (Links to External Site)
|Underlying OS: Windows (NT), Windows (2000), Windows (2003), Windows (XP)|
Source Message Contents
Subject: Alert:Microsoft Security Bulletin - MS02-011|
Authentication Flaw Could Allow Unauthorized Users To Authenticate To SMTP Service
Originally posted: February 27, 2002
Impact of vulnerability: Mail relaying.
Maximum Severity Rating: Low
Recommendation: Customers who need the Windows 2000 SMTP services should apply the Windows patch; all others should disable the SMTP
service. Customers using the Exchange Server 5.5 IMC should apply the Exchange Server 5.5 IMC patch.
- Microsoft Windows 2000
- Microsoft Exchange Server 5.5
An SMTP service installs by default as part of Windows 2000 server products and as part of the Internet Mail Connector (IMC) for Microsoft
Exchange Server 5.5. (The IMC, also known as the Microsoft Exchange Internet Mail Service, provides access and message exchange
to and from any system that uses SMTP). A vulnerability results in both services because of a flaw in the way they handle a valid
response from the NTLM authentication layer of the underlying operating system.
By design, the Windows 2000 SMTP service and the Exchange Server 5.5 IMC, upon receiving notification from the NTLM authentication
layer that a user has been authenticated, should perform additional checks before granting the user access to the service. The vulnerability
results because the affected services don't perform this additional checking correctly. In some cases, this could result in the
SMTP service granting access to a user solely on the basis of their ability to successfully authenticate to the server.
An attacker who exploited the vulnerability could gain only user-level privileges on the SMTP service, thereby enabling the attacker
to use the service but not to administer it. The most likely purpose in exploiting the vulnerability would be to perform mail relaying
via the server.
- Exchange 2000 servers are not affected by the vulnerability because they correctly handle the authentication process to the SMTP
- The vulnerability would not enable the attacker to read other users' email, nor to send mail as other users.
- Best practices recommend disabling unneeded services. If the SMTP service has been disabled, the mail relaying vulnerability could
not be exploited.
- The vulnerability would not grant administrative privileges to the service, nor would it grant the attacker the ability to run programs
or operating system commands.
Vulnerability identifier: CAN-2002-0054
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