Understanding E-mail Spoofing
by Deb Shinder - WindowSecurity.com - Monday, 25 October 2004.
If you receive a snail mail letter, you look to the return address in the top left corner as an indicator of where it originated. However, the sender could write any name and address there; you have no assurance that the letter really is from that person and address. E-mail messages contain return addresses, too – but they can likewise be deliberately misleading, or “spoofed.” Senders do this for various reasons, including:
  • The e-mail is spam and the sender doesn’t want to be subjected to anti-spam laws
  • The e-mail constitutes a violation of some other law (for example, it is threatening or harassing)
  • The e-mail contains a virus or Trojan and the sender believes you are more likely to open it if it appears to be from someone you know
  • The e-mail requests information that you might be willing to give to the person the sender is pretending to be (for example, a sender might pose as your company’s system administrator and ask for your network password), as part of a “social engineering” attack
  • The sender is attempting to cause trouble for someone by pretending to be that person (for example, to make it look as though a political rival or personal enemy said something he/she didn’t in an e-mail message)

Note: “Phishing” – the practice of attempting to obtain users’ credit card or online banking information, often incorporates e-mail spoofing. For example, a “phisher” may send e-mail that looks as if it comes from the bank’s or credit card’s administrative department, asking the user to log onto a Web page (which purports to be the bank’s or credit card company’s site but really is set up by the “phisher”) and enter passwords, account numbers, and other personal information.

Whatever the motivation, the objective of spoofed mail is to hide the real identity of the sender. This can be done because the Simple Mail Transfer Protocol (SMTP) does not require authentication (unlike some other, more secure protocols). A sender can use a fictitious return address or a valid address that belongs to someone else.

Receiving mail from spoofed addresses ranges from annoying to dangerous (if you’re taken in by a “phisher”). Having your own address spoofed can be even worse. If a spammer uses your address as the return address, you may suddenly find yourself inundated with angry complaints from recipients or even have your address added to “spammer” lists that results in your mail being banned from many servers.

How Spoofing Works

In its simplest (and most easily detected) form, e-mail spoofing involves simply setting the display name or “from” field of outgoing messages to show a name or address other than the actual one from which the message is sent. Most POP e-mail clients allow you to change the text displayed in this field to whatever you want. For example, when you set up a mail account in Outlook Express, you are asked to enter a display name, which can be anything you want, as shown in Figure 1.

Fig 1: Setting the display name in your e-mail client

The name you set will be displayed in the recipient’s mail program as the person from whom the mail was sent. Likewise, you can type anything you like in the field on the following page that asks for your e-mail address. These fields are separate from the field where you enter your account name assigned to you by your ISP. Figure 2 shows what the recipient sees in the “From” field of an e-mail client such as Outlook.

Fig 2: The recipient sees whatever information you entered


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