[unisog] sendmail vulnerability / impact

Phil.Rodrigues at uconn.edu Phil.Rodrigues at uconn.edu
Fri Mar 7 19:55:04 GMT 2003

(Another reply to keep it in the same thread.  My filter embarrassingly 
tagged Morrow's response at spam...)

What are the issues with blocking outbound port 25 traffic except from 
"registered" or known mail servers?  I am interested in doing it to help 
block outbound viral infections that use email to spread (like most of 

One concern I heard voiced is that it would impact people's ability to pop 
their mail from an external server.  Any others?


PS - We aggressively scanned for sendmail servers on campus, and are 
working with their admins to get them patched.  We have no plans to block 
inbound port 25 based on the sendmail vulnerability alone.  If a 
wide-scale exploit was available our stance would change.

Philip A. Rodrigues
Network Analyst, UITS
University of Connecticut

email: phil.rodrigues at uconn.edu
phone: 860.486.3743
fax: 860.486.6580
web: http://www.security.uconn.edu

"H. Morrow Long" <morrow.long at yale.edu>
03/07/2003 11:39 AM

        To:     Robin Anderson <robin at umbc.edu>
        cc:     unisog at sans.org
        Subject:        Re: [unisog] sendmail vulnerability / impact

We have a plan to block all TCP port 25 traffic into our campus network
beginning this summer.  We are just in the planning stage.  We plan to
offer MX records for any hosts/departments who insist that they need to
run their own Email servers and receive email on them.  The MX records
would provide for automatic relaying via our main campus email relays.
We already offer this as a service to departments (having mail for their
hosts/domains relayed from the Internet to/them via our relays and MX).
In a very few cases we may 'punch' TCP port 25 'holes' through the block
to some servers.  We are looking at automating the request procedure for
requesting MX record and relaying and/or an exception to the port 25 

BTW, though security plays a part (particularly since the sendmail 
hole) the primary reason we are interested in this is to prevent more 
via open relays when people accidently bring up SMTP servers.

H. Morrow Long

Robin Anderson wrote:
> In response to the most recently published sendmail vulnerability, we 
> given permission to block inbound port 25 traffic at our ResNet border.
> To date, we've only received one complaint about this action, but our 
> wants us to ask other university security folks about what they have 
> So here goes:
> 1) Has anyone else summarily blocked port 25 traffic (in or out) for
>    their ResNet?
>   a) If you have NOT blocked port 25, have you had problems/incidents
>      relating to the sendmail vulnerability?  Do you have a generally
>      laissez-faire approach to ResNet, or do you try to alert them to 
>      vulnerabilities, fixes, etc?
>   b) If you HAVE blocked port 25, do you have any data to support it as 
>      good decision?  (I know it's hard to prove a negative and that "we
>      haven't been hacked, so it must be working" is sometimes the best 
>      can offer.)  Any complaints?
> 2) Has anyone seen evidence of the exploit (successful or not) at their
>    site?
> Basically, our CIO is considering lifting the port 25 ban if no one has
> seen activity related to the sendmail hole.  Even evidence of a couple
> compromised systems or broad probes for the hole across multiple sites
> might keep the lockdown in place.  Thanks in advance!
> ---
> Robin Anderson  Unix SysAdmin, Specialist / Security
> Office of Information Technology               Univ. of MD, Baltimore 
County (UMBC)
> PGP fingerprint: (resumbc99) 1024/5B5A87A
> DA F3 7F 1E D3 75 28 9F  75 7D 6A 0C 10 8D CE 35
> "Pulvis et umbra sumus." (We are but dust and shadow.)  --  Horace

More information about the unisog mailing list