Can Received: fields be spoofed?
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Thread: Can Received: fields be spoofed?

  1. #1
    Some Assembly Required ShagDevil's Avatar
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    Can Received: fields be spoofed?

    In the recent weeks, I've had to deal with some pissed off people sending emails back to the company because they contained viruses or some malicious content. Now, I know how easily the From and other parts of the email can be easily forged. Basically what's going on, is some smartass or multiple smartasses are going to our company website, copying the account names and forging the header information and sending emails to random people with virii and the like making it appear to the common user, that we're sending out dirty emails.

    I understand the basics of email spoofing and how to trace the full path of an email .I also determined that this is indeed the work of an outsider (not a trojan/virus or co-worker). The emails are definately originating from mail servers outside our network. With all that being said, I was actually wondering if it's possible to spoof the IP in the Received: field in the email header. From my understanding, it's not possible (and this is what I've been using to trace the emails).
    According to the sites I've checked, they all seem to agree that while some parts of the Received: field can be forged, the IP cannot. How true is this?
    The object of war is not to die for your country but to make the other bastard die for his - George Patton

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    The IP cannot be forged, the attacker can however use a proxy to connect to a mailserver and thus his IP won't be visible to you.
    The above sentences are produced by the propaganda and indoctrination of people manipulating my mind since 1987, hence, I cannot be held responsible for this post\'s content - me

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    Anything in an email message can be spoofed except for the headers that the recipient's mail server puts there. Just because it says it originated somewhere or that it passed through certain mail servers doesn't mean it actually did. Mail can be sent by telnetting to port 25 on a mail server and typing the commands manually. Since that is possible one could make an email message look like it routed through any mailserver one wanted. The mail server that the sender sends the message to (and any downstream servers) would also add a received header which the malicious sender would not be able to control.

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    attacker can also use a smtp server that belongs to an innocent company. You cant believe how much smtp relays are open worldwide....
    I think there is some smtp relays on east (russia and likely) that everybody can use.
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  5. #5
    Senior Member OverdueSpy's Avatar
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    ShagDevil - I deal with the same issue on a daily basis. The easiest option for me was to draft a standard canned answer. It's not really a good option for me, but it is doable. Wish I could offer you a solutions but I think we are both in the same leaky boat.
    The mentally handicaped are persecuted in this great country, and I say rightfully so! These people are NUTS!!!!

  6. #6
    Some Assembly Required ShagDevil's Avatar
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    jonathans_daddy, So what you're saying is, that a malicious user can add as many Received: fields as they want to an email and even attach valid IP's to make it seem like the email did indeed go through mail servers that it never did?.

    Is it possible that a malicious user who received an email from my company at some point, to expand the full valid path in the email header, then use any old random mail server, forge in the appropriate Received: fields (that they copied from a valid email my company sent) with valid IP's and mail servers and create an email that for all practical purposes, will appear to have come from within my network?

    It would seem that if that is indeed the case, the only way to determine if an email originated from within my network would be to actually monitor all outgoing emails (which we currently do) and tracing emails through server transactions, would be utterly pointless.

    **note - I just thought about something else. Don't the mail servers keep records of transactions? Wouldn't it be possible to take an email, even with Received fields that made it appear as though it came from within my network and compare it to some database on the actual mail server itself? I know most (if not all) mail servers attach an ID number to the transaction. no?
    The object of war is not to die for your country but to make the other bastard die for his - George Patton

  7. #7
    AO Ancient: Team Leader
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    Erm.... Unless the headers show IP's or Mail Servers that belong to your company when they arrive at the pissed off party's mail client then this is all really rather normal activity.

    Other people outside your company have viruses infecting their machine. They harvest email addresses from all over the infected machines hard drive including, (in some cases), cached web pages in the users history folders. They then pick a name at random and place that in the "from" field and send out a copy to everyone except the the user in the "from" field. This is to make it more difficult for the infected machine to be tracked down. There are a thousand viruses out there right now that act in this fashion.

    The interesting side effects of this behaviour are as follows:-

    1. Your users proudly tell you that they didn't open the attachment because they didn't recognize the sender.
    2. Your users complain about NDR's from people they never sent messages to because they don't know them.
    3. Your users forward the bitch fits of others to you accusing your company of being infected with a virus and telling them to "please try to be more professional" - It's a bitch when the pissed off party reads my reply - they go all nice and apologetic....

    In any of these cases it's the virus activity not some malicious bastige trying to make your company look bad. To prove that try to talk the pissed off party into sending you the original headers. I bet you won't find anything to do with your company in them...... But don't expect the pissed off party to have looked at the headers and understood them.
    Don\'t SYN us.... We\'ll SYN you.....
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    That's probably what it is, but what if it isn't? If I'm correct, smtp doesn't have any authentication built in, so wouldn't it be pretty easy to do what ShagDevil is talking about?
    As long as you don't expect an answer back, can't you just spoof all the headers, including the IP?

  9. #9
    Some Assembly Required ShagDevil's Avatar
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    Tiger Shark lol
    You should have seen the looks I recently got when I tried to explain to my co-workers how to break down an email header and find the fields needed in order to see where the email may have originated. I might as well have been talking swahili.
    We did receive a couple of the spoofed emails back and to my pleasure, not one of the received fields in any of the emails was even remotely close to any mail server we use. The hard part is convincing these outside people that we didn't send the malicious email in the first place. why? because exactly like you said, they don't understand how to read headers. go figure.
    I've come to a conculsion on how to resolve the problem though.
    1) disable all email capabilities
    2) hand out free pens and envelopes
    3) hire a clown so they stop looking at me all funny
    4) quit
    5) move to switzerland and start a farm

    I've also recently figured out a mathmatical formula to determine the stress level for a LAN admin.
    number of users * number of complaints * blue screens of death / a batch of mom's homemade chocolate chip cookies = stress level.
    The object of war is not to die for your country but to make the other bastard die for his - George Patton

  10. #10
    AO Ancient: Team Leader
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    Shag: I don't try to convince them. I send a slightly concescending email informing them of how this works and how the email could not possibly have emanated from my domain because of x, y and z. Then I point out how surprised I am that their IT chap hasn't explained this to them so they don't go pissing off admins of other domains by accusing them of not knowing their job....... It works for me......

    3) hire a clown so they stop looking at me all funny
    4) quit
    5) move to switzerland and start a farm
    ROFLMAO
    Don\'t SYN us.... We\'ll SYN you.....
    \"A nation that draws too broad a difference between its scholars and its warriors will have its thinking done by cowards, and its fighting done by fools.\" - Thucydides

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