Event ID:1035 SmtpReceive

I see these errors about 1 - 3 a day every day. No idea if its one i should ignore or not. No user is complaining about emails. I started seeing these issues a month after i did windows updates on the exchange server.


Log Name:      Application
Source:        MSExchangeTransport
Date:          1/12/2014 6:10:13 PM
Event ID:      1035
Task Category: SmtpReceive
Level:         Warning
Keywords:      Classic
User:          N/A
Computer:      DH11.Abc.com
Description:
Inbound authentication failed with error LogonDenied for Receive connector Default DH11 The authentication mechanism is Ntlm. The source IP address of the client who tried to authenticate to Microsoft Exchange is [203.223.xxx.xxx].
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="MSExchangeTransport" />
    <EventID Qualifiers="32772">1035</EventID>
    <Level>3</Level>
    <Task>1</Task>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2014-01-12T23:10:13.000000000Z" />
    <EventRecordID>556303</EventRecordID>
    <Channel>Application</Channel>
    <Computer>DH11.Abc.com</Computer>
    <Security />
  </System>
  <EventData>
    <Data>LogonDenied</Data>
    <Data>Default DH11</Data>
    <Data>Ntlm</Data>
    <Data>203.223.xxx.xxx</Data>
  </EventData>
</Event>
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Patrick BogersDatacenter platform engineer LindowsCommented:
Hi

Sounds like a malicious user is trying to get access to your recieveconnector.
You have anonymised its ip adress, try www.infosniper.net and see where it is getting from, my bet is on a country you dont expect traffic from. Just block the ip address once you know.

*Edit, this has been answered before in this thread.
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IT_FanaticAuthor Commented:
Block it wear on the firewall? The ip address always changes and its from different countries
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Will SzymkowskiSenior Solution ArchitectCommented:
This would most likely be an attack of some sort. Check the orign of the IP address to ensure it is not known. I would then take a look at your firewall to see if this IP address has attempted to access anything else on your network using different ports.

What ports are these IP addresses coming in on? 25? In some cases 3389 (RDP) port might be open. As this is a receive connector it is probably port 25 smtp, 110/995, pop3, 143/993 IMAP.

Will.
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Patrick BogersDatacenter platform engineer LindowsCommented:
Hi again,

You can block it in ESM or firewall but i have to say you do not need to worry to much.
Nowadays there are many spam bots scanning the internet for badly configured exchange servers. As long as you have configured your machine well i wouldnt mind to much.
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Will SzymkowskiSenior Solution ArchitectCommented:
I would have to disagree with Patrick in regards to just leaving it. From a security perspective if you have multiple Public IP's that are attempting to get into your environment everyday then this is a concern. I would be worried about what other things are trying to be compromised.

Check the logs on your firewall tracing back to the Public IP's that have been logged. Check what ports they are coming in on and also what other prossible servers they are trying to connect to.

Will.
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Patrick BogersDatacenter platform engineer LindowsCommented:
Dear Will, where did you read me advising "just leaving it"?

I advised to block the ip addressess once identified being unwanted but also not to worry to much (as a beginning admin could scare himself to death with this kind of error).
Every public available server is target for spam/crawl bots and thousands of scriptkiddies so as long as the machine is firmly configured what can you do beside maintaing updates and monitor?   (besides IDS,IPS, Barracuda filtering etc etc)
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Will SzymkowskiSenior Solution ArchitectCommented:
You can block it in ESM or firewall but i have to say you do not need to worry to much.

Yes you did mention blocking the IP via firewall but, ultimately there is a bigger issue here. Simply blocking the IP will not resolve the askers issue. As it will most likely reoccur.  There is definetly a configuration flaw with Exchange and or the Network side (firewall). Simply Blocking the single IP or small group of IP's does not resolve this issue.

IMO He should be checking the logs on the firewall to see why all of these Public IP's are getting inside his network.

Will.
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Md. MojahidCommented:
This issue occurs if the Exchange server cannot authenticate with the remote Exchange server. Exchange servers requires authentication to route internal user messages between servers. The issue can be caused by one of the following reasons:
The Exchange server is experiencing Time synchronization issues
The Exchange server is experiencing Service Principal Name (SPN) issues
The required TCP/UDP ports for the Kerberos protocol are blocked by the firewall.


http://support.microsoft.com/kb/979174
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IT_FanaticAuthor Commented:
My firewall shows nothing. The warnings only come from the exchange server. I saw this under the windows logs >security. Its the same time as the warning that shows on the windows logs>application. This user doesn't exists. If this is malice. How can I stop it? The network has not changed at all other than running windows updates.



An account failed to log on.

Subject:
      Security ID:            NETWORK SERVICE
      Account Name:            DH11-$
      Account Domain:            ABC
      Logon ID:            0x3e4

Logon Type:                  8

Account For Which Logon Failed:
      Security ID:            NULL SID
      Account Name:            michelle@abc.com
      Account Domain:            

Failure Information:
      Failure Reason:            Unknown user name or bad password.
      Status:                  0xc000006d
      Sub Status:            0xc0000064

Process Information:
      Caller Process ID:      0xc18
      Caller Process Name:      A:\Program Files\Microsoft\Exchange Server\V14\Bin\EdgeTransport.exe

Network Information:
      Workstation Name:      DH11
      Source Network Address:      -
      Source Port:            -

Detailed Authentication Information:
      Logon Process:            Advapi  
      Authentication Package:      Negotiate
      Transited Services:      -
      Package Name (NTLM only):      -
      Key Length:            0

This event is generated when a logon request fails. It is generated on the computer where access was attempted.

The Subject fields indicate the account on the local system which requested the logon. This is most commonly a service such as the Server service, or a local process such as Winlogon.exe or Services.exe.

The Logon Type field indicates the kind of logon that was requested. The most common types are 2 (interactive) and 3 (network).

The Process Information fields indicate which account and process on the system requested the logon.

The Network Information fields indicate where a remote logon request originated. Workstation name is not always available and may be left blank in some cases.

The authentication information fields provide detailed information about this specific logon request.
      - Transited services indicate which intermediate services have participated in this logon request.
      - Package name indicates which sub-protocol was used among the NTLM protocols.
      - Key length indicates the length of the generated session key. This will be 0 if no session key was requested.
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Will SzymkowskiSenior Solution ArchitectCommented:
Does your Exchange traffic go through you firewall? You should not have your internal CAS servers facing directly to the internet (if this is how it is setup) all traffic should be going through a firewall or another appliance that is in your DMZ.


Will.
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IT_FanaticAuthor Commented:
we use postini which is the middle man of our inbound and outbound emails. So once they filter an email it gets released to us and vice verse.

We have a sonicwall. Onsite. Like I said it makes no sense as this network hasnt had these warning in years and now all of a sudden when nothing has changed at all. Its only 2-3 warning a day or at times 1-2 warning every other day,

Regardless i see access is denied. So in reality am i safe?
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Patrick BogersDatacenter platform engineer LindowsCommented:
Yes i believe so,

My guess you have the windows firewall doing the firewalling for the exchange which (by default) only logs denied connection attempts.

Never the less you should keep a regulair track of the logs or even temporarily log also accepted connections but these logs grow like bunnies.

ONCE you find ip adressess that brute force to OWA or to exchange it can be rewarding to find out to which ISP that ip address belong and send a mail to abuse@isp-name.domain sending a short piece of log and request to take the server down, in my experience they are very reactive to this.
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IT_FanaticAuthor Commented:
Could a windows update have caused this? Or basically the world is getting more spam crazy than normal?
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Patrick BogersDatacenter platform engineer LindowsCommented:
Come to think about it 1-3 times a day, i suspect it is people using (ze)nmap in verbose mode which scans a range of ports and once SMTP found it will make one bogus call only to identify what exchange engine is behind that port.
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IT_FanaticAuthor Commented:
which means?
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Patrick BogersDatacenter platform engineer LindowsCommented:
Script kiddies or the Chinese :).

Suppose your ip adress is    93.62.100.126

And i am a script kiddie who want to have my computer working hard at night and configure a port scan 0-64000 in verbose mode on 92.62.0 0 to 92.62.255.255

I would hit your ip adress and would scan all ports between 0-64000 where i would find ports 25,80,443 maybe 3389 and the tool will try to identify what server technique is behind those ports so it would make an call to exchange (which you see failing offcourse), also make a call to port 80 to identify what webserver is being used etc etc

In the real pentest world we can determine weaknessess identified by such a tool. But for fun youngster (not to forget the chinese) just randomly scan hoping to hit the jackpot or hunnypot.(latter is a server that is intentionally left onprotected to catch hackers)
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IT_FanaticAuthor Commented:
Any recommendations?
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Patrick BogersDatacenter platform engineer LindowsCommented:
Like us we have morning-checklists which we go through every morning which includes checking unauthorized connection attempts. One or 2 we ignore, hundreds we report to the ISP.
If we recognise a big CIDR block, we block them all together but use with caution.

For services like OWA you could ask yourself if it is being used? if not turn it off.
(i think this is the cause of your logs as we see no destination ip address in the logs. Attempts to OWA are logged by the system itself and the networkservice)
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IT_FanaticAuthor Commented:
we use OWA. Especially if people are out of the office. so basically 1-2 a day is common? Unless its gets to a ridiculous amount per day than its time to be concerned?
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Patrick BogersDatacenter platform engineer LindowsCommented:
That is my opinion yes.

If you would like to learn how they find your OWA portal, try this google dork as a search in google

inurl:owa/auth/logon.aspx

You will be amazed how many OWA portals it reveals.

If you do not want to be found that easy put a file called robots.txt in the root of your website and put below code in it:

# Make changes for all web spiders
User-agent: *
Disallow: /

It will prevent search engines to crawl your (private) website where OWA is part off.
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IT_FanaticAuthor Commented:
Thanks everyone for your help.
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IT_FanaticAuthor Commented:
Thanks everyone for your help and input
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IT_FanaticAuthor Commented:
Hi Patricksr1972

I still see this error every other day or nothing for like 3 days.

I see in windows log>security at the time of this warning looks like someone is trying to login with fake users names that don't belong to us.

Of course they can't get in. So looks like the firewall is doing it's job.

Should I continue to ignore this?

Is this something common that all environments go through?
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IT_FanaticAuthor Commented:
Hi Patricksr1972

I still see this error every other day or nothing for like 3 days.

I see in windows log>security at the time of this warning looks like someone is trying to login with fake users names that don't belong to us.

Of course they can't get in. So looks like the firewall is doing it's job.

Should I continue to ignore this?

Is this something common that all environments go through?
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Patrick BogersDatacenter platform engineer LindowsCommented:
Hi,

Yes you can safely ignore them unless you start seeing thousands and thousands of request.
Just a few every now and then is pretty normal for an internet facing machine.

Port scans are pretty normal and we all see them.
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IT_FanaticAuthor Commented:
Thanks man. I appreciate it.
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WPLGCommented:
I have been experiencing the same issue and am very concerned about it because I am receiving hundreds a day.  We have blocked Russia and China IP addresses via a script Cisco has to compile country IP addresses but we are now receiving from other countries.  the one thing we did change was our Internet circuit with Comcast.  I have attached one of the SMTP receive logs.  Any advice would be appreciated.
RECV20150607-2.LOG
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IT_FanaticAuthor Commented:
I would suggest you contact Comcast and change your IP block
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