Difference between revisions of "Email Headers"

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(Message Id Field: - Added link)
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== Message Id Field ==
 
== Message Id Field ==
 
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{{main|Using message id headers to determine if an email has been forged}}According to the current guidelines for email [http://www.faqs.org/rfcs/rfc2822.html], every message should have a Message-ID field. These id fields can be used to determine if a message has been forged. It is harder, but sometimes possible, to show that a message is authentic using the message id field. Where known, the Message-ID algorithms for known programs are [[List of MUA Header Formats|given on the separate pages for those programs]].
According to the current guidelines for email [http://www.faqs.org/rfcs/rfc2822.html RFC 2822]), every email should have a Message-ID field:
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<pre>  The "Message-ID:" field provides a unique message identifier that
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  refers to a particular version of a particular message. The
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  uniqueness of the message identifier is guaranteed by the host that
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  generates it (see below).  This message identifier is intended to be
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  machine readable and not necessarily meaningful to humans.  A message
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  identifier pertains to exactly one instantiation of a particular
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  message; subsequent revisions to the message each receive new message
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  identifiers.
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  ...
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  The message identifier (msg-id) itself MUST be a globally unique
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  identifier for a message.  The generator of the message identifier
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  MUST guarantee that the msg-id is unique.  There are several
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  algorithms that can be used to accomplish this.  Since the msg-id has
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  a similar syntax to angle-addr (identical except that comments and
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  folding white space are not allowed), a good method is to put the
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  domain name (or a domain literal IP address) of the host on which the
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  message identifier was created on the right hand side of the "@", and
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  put a combination of the current absolute date and time along with
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  some other currently unique (perhaps sequential) identifier available
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  on the system (for example, a process id number) on the left hand
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  side. Using a date on the left hand side and a domain name or domain
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  literal on the right hand side makes it possible to guarantee
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  uniqueness since no two hosts use the same domain name or IP address
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  at the same time.  Though other algorithms will work, it is
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  RECOMMENDED that the right hand side contain some domain identifier
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  (either of the host itself or otherwise) such that the generator of
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  the message identifier can guarantee the uniqueness of the left hand
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  side within the scope of that domain.</pre>
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Where known, the Message-ID algorithms for known programs are [[List of MUA Header Formats|given on the separate pages for those programs]].
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== Sample Header ==  
 
== Sample Header ==  

Revision as of 13:24, 21 April 2007

Email Headers are lines of metadata attached to each email that contain lots of useful information for a forensic investigator. However, email headers can be easily forged, so they should never be used as the only source of information.

Making Sense of Headers

There is no single way to make sense of email headers. Some examiners favor reading from the bottom up, some favor reading from the top down. Because information in the headers can be put there by the user's MUA, a server in transit, or the recipient's MUA, it can be difficult to determine when a line was added.

Mail User Agents

Every MUA sets up the headers for a message slightly differently. Although some headers are required under the applicable RFC, their format and ordering can vary by client. Almost all clients, however, add their headers in a fixed format and order. The examiner can use the format and order for each client to show that messages were forged, but not that they were legitimate. For example, if a message purports to be from Apple Mail but the order or the headers do not match the Apple Mail Header Format, the message has been forged. If the headers of the message do match that format, however, it does not guarantee that the message was sent by that program.

Servers in Transit

Mail servers can add lines onto email headers, usually in the form of "Received" lines, like this:

Received: by servername.recipeienthost.com (Postfix, from userid 506)
	id 77C30808A; Sat, 24 Feb 2007 20:43:56 -0500 (EST)

Message Id Field

Main article Using message id headers to determine if an email has been forgedAccording to the current guidelines for email [1], every message should have a Message-ID field. These id fields can be used to determine if a message has been forged. It is harder, but sometimes possible, to show that a message is authentic using the message id field. Where known, the Message-ID algorithms for known programs are given on the separate pages for those programs.

Sample Header

This is an (incomplete) excerpt from an email header:

Received: from lists.securityfocus.com (lists.securityfocus.com [205.206.231.19])
        by outgoing2.securityfocus.com (Postfix) with QMQP
        id 7E9971460C9; Mon,  9 Jan 2006 08:01:36 -0700 (MST)
Mailing-List: contact forensics-help@securityfocus.com; run by ezmlm
Precedence: bulk
List-Id: <forensics.list-id.securityfocus.com>
List-Post: <mailto:forensics@securityfocus.com>
List-Help: <mailto:forensics-help@securityfocus.com>
List-Unsubscribe: <mailto:forensics-unsubscribe@securityfocus.com>
List-Subscribe: <mailto:forensics-subscribe@securityfocus.com>
Delivered-To: mailing list forensics@securityfocus.com
Delivered-To: moderator for forensics@securityfocus.com
Received: (qmail 20564 invoked from network); 5 Jan 2006 16:11:57 -0000
From: YJesus <yjesus@security-projects.com>
To: forensics@securityfocus.com
Subject: New Tool : Unhide
User-Agent: KMail/1.9
MIME-Version: 1.0
Content-Disposition: inline
Date: Thu, 5 Jan 2006 16:41:30 +0100
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Message-Id: <200601051641.31830.yjesus@security-projects.com>
X-HE-Spam-Level: /
X-HE-Spam-Score: 0.0
X-HE-Virus-Scanned: yes
Status: RO
Content-Length: 586
Lines: 26

External Links