SMTP daemon supports EHLO
| smtp-ehlo (323) |  Low Risk |
Description:
SMTP daemons that support Extended HELO (EHLO) can release information that could be useful to an attacker in performing an attack. Attackers have been known to use the EHLO command to determine configuration information on SMTP daemons.
Platforms Affected:
- Apple, Mac OS
- Compaq, Tru64
- Data General, DG/UX
- HP, HP-UX
- IBM, AIX
- IBM, OS2
- Linux, Kernel
- Microsoft, Windows 2000
- Microsoft, Windows 2003 Server
- Microsoft, Windows 95
- Microsoft, Windows 98
- Microsoft, Windows 98SE
- Microsoft, Windows Me
- Microsoft, Windows NT 4.0
- Microsoft, Windows Vista
- Microsoft, Windows XP
- SCO, SCO Unix
- SGI, IRIX
- Sun, Solaris
- Various vendors, SMTP servers
- WindRiver, BSDOS
Remedy:
SMTP as defined in RFC 2821 (see References) requires EHLO. Some SMTP implementations allow you to disable EHLO, but this capability is neither required nor consistent across products.
If you are uncomfortable with the information that the Extended SMTP features can reveal, you may choose to disable EHLO on your mail server (if applicable), or switch to a mail server that allows EHLO to be disabled. Consult your mail server documentation or contact your vendor for information on whether it is possible to modify your mail server configuration to disable EHLO.
Consequences:
Obtain Information
References:
- Microsoft Exchange 5.5 Product Documentation, Disabling ESMTP Support at http://www.microsoft.com/Exchange/en/55/help/default.asp?url=/Exchange/en/55/help/documents/server/XOG05031.HTM.
- Request for Comments: 2821, Simple Mail Transfer Protocol at http://www.ietf.org/rfc/rfc2821.txt?number=2821.
- CVE-1999-0531: An SMTP service supports EXPN, VRFY, HELP, ESMTP, and/or EHLO.
Reported:
Not available
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