MIME Header Analysis in Email Forensics
The MIME (Multipurpose Internet Mail Extensions) headers of an email message can be critical in investigations. These headers contain potentially valuable metadata about the email's journey, origins, and authenticity.
The advantages and potential evidence that can be extracted from MIME headers include:
Detailed Message Structure:
MIME headers outline an email's structure, including its different parts (text, attachments, HTML), their types, and how they are encoded. This helps investigators understand the complete message content and identify any hidden or obfuscated information.
Authentication:
They provide crucial information for verifying an email's authenticity. This can be vital in investigations involving phishing, spoofing, or other forms of email fraud.
Email Source Verification:
The headers help verify the legitimacy of the sender by revealing the originating IP address, email server details, and other metadata.
Tracking the Email's Path:
Provides a detailed record of the email's journey through multiple servers and networks, identifying possible points of alteration or tampering.
Detection of Spoofing and Phishing:
Anomalies in the "From," "Return-Path," and "Received" fields can reveal signs of email spoofing or phishing attempts.
Determining Time of Email Transmission:
The headers contain timestamp information from each server the email passed through, allowing investigators to construct a timeline.
Identifying Potential Tampering:
Changes or inconsistencies in the header fields can indicate that the email has been manipulated after its original transmission.
Email Client, System Information and Protocols Used:
MIME headers provide information about the email client (Outlook, Gmail, etc.), operating system, and protocols used (SMTP, POP3, IMAP), which may aid in recreating the email environment.
Evidence of Attachments:
They describe attached files, including their type, encoding, and boundaries. This information can be important for validating whether attachments were included or altered.
Authentication via DKIM/SPF and ARC Records:
SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail) and ARC (Authenticated Received Chain) information in headers can be used to authenticate the sender's domain and detect forgery.
Objective Evidence:
MIME headers are less susceptible to manipulation than the email body. They offer objective evidence that can corroborate or refute claims made by suspects or witnesses.
Automation and Scalability:
The structured format of MIME headers allows for automated analysis and extraction of key information, essential when dealing with large volumes of email data in forensic investigations.
Potential Evidence from MIME Headers:
IP Address of Sending Server:
The originating IP address is often found in the "Received" header, providing key evidence to track the sender's location or network.
Email Routing Information:
The "Received" field logs every server that handled the email, offering a path analysis from sender to recipient.
Authentication Information:
SPF, DKIM, and DMARC authentication results can show whether the email passed validation checks, indicating if the message is genuine or spoofed.
Sender's Email Client and Operating System:
The User-Agent header reveals the email client (e.g., Outlook, Gmail) and sometimes the operating system used to compose the email.
Timestamp Evidence:
Each mail server's timestamp shows the precise time when the email was handled, which helps establish the exact timeline of email delivery.
Hidden Content:
MIME headers can sometimes reveal hidden content or metadata embedded within the email, such as tracking pixels, hidden comments, and hidden timestamps, that might not be visible to the recipient.
Reply-To Address:
The "Reply-To" header can differ from the "From" address, potentially revealing the intended response destination. This is often used in phishing and email obfuscation schemes.
X-Mailer or User-Agent Information:
This field indicates the software or platform used to send the email, which may be important in cases where specific software is known to be used by the email's sender.
Subject and Encoding Information:
The "Subject" and encoding details in the headers can reveal if the subject line has been altered or if non-standard character sets are used, which is common in phishing attacks.
Content Type, Attachment and Encoding Information:
Identifies whether the email contains HTML, plain text, or attachments and how the content was encoded (e.g., base64), which helps analyse malicious payloads.
BCC (Blind Carbon Copy) Recipients:
BCC headers (if visible or logged) can provide insight into other recipients the sender attempted to hide.
Message Read Status:
Capturing whether a message is marked as "read" or "unread," including historical "read" or "unread" status, for example, whether the end-user read a message and then marked it as "unread," can answer questions to determine what else they did and when.
Other Spoofing and Forgery Indicators:
Inconsistencies or anomalies in the From, Reply-To, or other headers can indicate attempts to spoof the sender's address or forge the email's origin.
By extracting and analysing these details from the MIME headers, forensic investigators can uncover evidence about the email's origin, authenticity, and potential malicious intent.
