Hypercraft - HackTheBox Challenge Writeup

Challenge Information

Description

In this challenge, we receive a suspicious email claiming to be from Axel Knight, a missing agent. The organization suspects the email may be a phishing attempt from the Arodorians rather than legitimate communication. Our task is to analyze the email forensically to determine its authenticity and extract the flag if it’s genuine.

The challenge requires us to:

• Examine email headers and metadata
• Identify spoofing or forgery indicators
• Verify the legitimacy of the sender
• Extract the flag from the analysis

Solution

Initial Analysis

The key to solving this challenge lies in examining the email metadata and headers carefully. Phishing emails often contain subtle inconsistencies in headers, sender information, or embedded content that reveal their true origin.

Key Steps

1. Extract and Examine Email Headers

Start by extracting the raw email file and examining its headers:

# Display the raw email content
cat suspicious_email.eml

# Look for critical headers
grep -i "from:\|return-path:\|authentication-results:\|dkim-signature:\|spf:" suspicious_email.eml

2. Check Authentication Records

Authentication headers (DKIM, SPF, DMARC) are crucial indicators:

# Look for authentication failures or missing records
grep -i "authentication-results" suspicious_email.eml
grep -i "dkim" suspicious_email.eml
grep -i "spf" suspicious_email.eml

3. Analyze Sender Information

Compare the “From” header with the “Return-Path” and other routing information:

# Extract sender details
grep -i "^from:" suspicious_email.eml
grep -i "^return-path:" suspicious_email.eml
grep -i "^reply-to:" suspicious_email.eml

4. Examine Email Body and Attachments

# Extract and analyze attachments
find . -name "*.eml" -exec strings {} \; | grep -i "attachment\|filename"

# Look for embedded objects or suspicious scripts
strings suspicious_email.eml | grep -i "script\|javascript\|executable"

5. Identify Phishing Indicators

Look for red flags such as:

• Mismatched sender addresses
• Failed authentication checks
• Unusual routing paths
• Request for sensitive information
• Urgency language or threats

6. Extract the Flag

Once you’ve confirmed the email is a phishing attempt (or verified it’s legitimate), the flag will typically be embedded in:

• Email headers as a custom field
• The body text as a hidden message
• Metadata of attachments
• Base64-encoded content

# Search for flag patterns
grep -i "flag\|HTB" suspicious_email.eml
strings suspicious_email.eml | grep "HTB{"

Tools Used

• File examination utilities: cat, strings, hexdump
• Text processing: grep, sed, awk
• Email analysis: Raw .eml file inspection
• Header parsing: Email RFC 5322 compliance checking

Key Learnings

1. Email authentication is critical: DKIM, SPF, and DMARC records provide verifiable proof of legitimate origin. Missing or failed authentication is a major red flag.

2. Header spoofing is common: The “From” header can be easily forged, but the “Return-Path” and received headers are harder to fake and reveal the true route.

3. Metadata tells the story: Email metadata often contains more truth than the message content itself. Always examine full headers.

4. Phishing indicators are systematic: Legitimate organizations maintain consistent sender information, proper authentication, and professional communication standards.

5. Defense in depth: Multiple verification methods (sender reputation, authentication records, content analysis) should be used together for accurate assessment.

The flag for this challenge: HTB{<redacted>}