[Snort-users] SMTP decoder

Joel Esler (jesler) jesler at ...589...
Wed Feb 11 16:50:50 EST 2015


You’ve got your two alternatives there.  Raise the limit, or suppress the alert.

Ask yourself what your action is going to be there.  “What am I going to do about a big SMTP server command”, if the answer is “nothing”, then suppress the alert.  If the answer is anything else, then use your best judgement as to what action you should take.

--
Joel Esler
Open Source Manager
Threat Intelligence Team Lead
Talos

On Feb 11, 2015, at 9:51 AM, Dan Roberts <danroberts2604 at ...11827...<mailto:danroberts2604 at ...11827...>> wrote:

Hello guys,

I'm running SNORT since a few months now, and I still get a lot of alerts like:

"(smtp) Attempted command buffer overflow: more than 512 chars ...."

In the snort.conf file, we find following parameter for the smtp decoder:

"max_command_line_len 512"

Although the maximum command line length is "strictly" limited to 512 by RFC 821 (HELO), the RFC 1869 (EHLO) authorize the extension of this limit:
... This specification extends the SMTP MAIL FROM and TO to allow additional parameters and parameter values. It is possible that the MAIL FROM and RCPT TO lines that result will exceed the 512 character limit on command line length imposed by RFC 821.
..."

How do you,  guys, manage this ?

Do you simply consider these alerts as FP ?
Have you raised the max_command_line_len limit ?

Cheers
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