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Investigating Phishing Emails: A SOC Analyst’s Guide

Gabriel Haab

• 2 min read
Investigating Phishing Emails: A SOC Analyst’s Guide

As a Security Operations Center (SOC) analyst, responding to potential phishing emails is a critical part of protecting your organization. Employees often report suspicious emails, and it’s your responsibility to investigate and determine whether they pose a genuine threat. Here's a structured approach to dissecting these emails effectively.

Step 1: Examine the Email Headers

Email headers are a goldmine of information. They provide insight into the journey of the email and help identify discrepancies.

Key Things to Check in Headers:

  1. Received Path: Track the email's journey from the sender's mail server to yours. Unexpected jumps or unusual server domains can indicate a spoofed email.
  2. From Address: Look at the domain in the From field. Does it match the sender's claimed identity? Attackers often use domains that appear similar to legitimate ones (e.g., “amaz0n.com” instead of “amazon.com”).
  3. Return-Path: This is often where phishing attempts show their true origin. A mismatch between the Return-Path and the From field could indicate a spoof.
  4. X-Originating-IP: This shows the IP address of the original sender. A quick WHOIS lookup can confirm if the IP belongs to a legitimate service or an unexpected geographical region.

Step 2: Check Email Authentication (SPF, DKIM, DMARC)

Modern email security mechanisms like SPF, DKIM, and DMARC help authenticate legitimate emails.

What to Look For:

  1. SPF (Sender Policy Framework): Ensure the sender's IP is authorized to send emails on behalf of the domain. Failure here suggests a spoofed domain.
  2. DKIM (DomainKeys Identified Mail): Verify that the email hasn’t been tampered with during transit. DKIM adds a digital signature and a mismatch indicates possible forgery.
  3. DMARC (Domain-based Message Authentication, Reporting, and Conformance): Check the DMARC policy to see how the domain handles emails failing SPF or DKIM checks. A strict DMARC policy is a sign of a well-managed domain, while a lack of one can leave room for abuse.

Step 3: Validate the Reply-To Address

Phishers often use a legitimate-looking From address while setting the Reply-To to a malicious email. Compare these fields carefully:

  • Is the Reply-To different from the From address?
  • Does the Reply-To domain raise any red flags (e.g., free email services like Gmail, especially for official correspondence)?

If the reply address is suspicious, you’re likely dealing with a phishing attempt.

Additional Tips for Phishing Email Investigation

  • Hover over Links: Without clicking, hover over any links to check the URL. Does it match the sender's domain, or is it a misleading lookalike?
  • Attachment Analysis: Attachments, especially .exe, .zip, or macro-enabled documents, often contain malware. Use a secure sandbox environment to analyze them.

Investigate Suspicious Language and Urgency

Phishing emails frequently use language that induces fear or urgency, such as:

  • “Your account will be locked in 24 hours.”
  • “Confirm your details immediately.”

Legitimate organizations rarely use such pressure tactics.

Leverage Threat Intelligence

Cross-reference the sender's domain, IP address, or URLs against known phishing databases or threat intelligence platforms. Tools like VirusTotal and PhishTank can quickly flag known threats.

Document Your Findings

A thorough investigation isn’t complete without documentation. Record all observations, including:

  • Header analysis
  • Authentication results
  • URL or attachment details

This documentation helps in:

  1. Training employees on future phishing detection.
  2. Reporting the incident to authorities if necessary.
  3. Enhancing your organization’s phishing defenses by updating filters and blocklists.

By following this structured approach, SOC analysts can swiftly identify and mitigate phishing threats. While email security tools automate parts of this process, human judgment remains irreplaceable in interpreting context and catching sophisticated attacks. Remember, every phishing email you neutralize is another step toward safeguarding your organization's digital assets.