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Introduction:
Modern phishing attacks no longer rely on obvious typos or broken English. Instead, threat actors craft contextually relevant messages—like fake alerts from France’s Assurance Maladie—and rely on urgency to bypass critical thinking. The key to defeating such attacks lies in disciplined email header analysis and understanding how simple anomalies (e.g., a missing country-code TLD) reveal malicious intent.
Learning Objectives:
- Analyze email headers to identify forged sender addresses and spoofed display names.
- Configure open-source and mainstream email clients to block remote content and disable automatic image loading.
- Use command-line tools (Linux/Windows) to verify domain legitimacy, check SPF/DKIM/DMARC, and safely investigate phishing URLs.
You Should Know:
- Email Header Forensics – Spotting the Real Sender Behind the Mask
Every email contains hidden headers that reveal the true path from sender to recipient. In the Assurance Maladie phishing example, the display name showed “Noreply@Assurance-Maladie” but the real envelope sender was “info@wowitsmassive[.]com”. Attackers abuse the difference between the “From” header (user‑facing) and the “Return-Path” or “Reply-To” fields.
Step‑by‑step guide to view and analyze headers:
- Gmail: Open email → three dots → “Show original” → look for “From:” and “Return-Path:” lines.
- Outlook (Windows): Double‑click email → File → Properties → “Internet headers” section.
- Thunderbird / Evolution / FairEmail: View → Headers → All (or use “View Source”).
- Linux command line (fetching headers without opening email):
Using curl to simulate a POP3/IMAP fetch requires credentials, but you can test a suspicious link via: curl -v --head https://www.assurance-maladie.fr Compare with similar domain For direct header extraction from an .eml file: cat suspicious_email.eml | grep -E "^(From|Return-Path|Reply-To|Sender):"
- Windows PowerShell (extract from saved .eml):
Get-Content suspicious_email.eml | Select-String -Pattern "^(From|Return-Path|Reply-To):"
What to verify:
- Does the `Return-Path` domain match the claimed organization’s real domain (e.g., `@ameli.fr` vs
@wowitsmassive.com)? - Is the TLD present and correct? (France’s Assurance Maladie uses
ameli.fr, not `Assurance-Maladie` without TLD). - Are there multiple `Received:` chains showing unexpected foreign IP addresses? Use `dig -x
` to check.
- Hardening Email Clients – Disable Remote Content and CSS Execution
In the conversation, Ines W. noted that FairEmail (open source) and Evolution Mail block images by default, while default Samsung client loads everything – including tracking pixels and malicious payloads.
Step‑by‑step guide to secure your client:
- FairEmail (Android):
Settings → “Display” → “Show images” → set to “Never” or “Only for contacts”.
Settings → “Privacy” → “Block remote content” → enabled.
Reference: https://email.faircode.eu/ -
Evolution Mail (Linux):
Edit → Preferences → Mail Preferences → HTML Mail → “Load images only if sender is in address book” or “Never load images remotely”. -
Microsoft Outlook (Windows registry to block all external images):
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Options\Mail Create DWORD: BlockAllExternalImages = 1
Or via GUI: File → Options → Trust Center → Automatic Download → “Don’t download pictures automatically”.
-
Thunderbird (cross‑platform):
Settings → Privacy & Security → Mail Content → “Allow remote content” → uncheck.
Add custom CSS to disable unwanted styling:
`about:config` → `mailnews.display.disable_formatting` → `true`.
Why this matters: Attackers often embed zero‑pixel images (web beacons) to confirm email opens and profile victims. Blocking remote content also prevents automatic exploitation of CSS‑based rendering bugs.
- DNS and TLD Verification – Don’t Trust the Display Name, Trust the Domain
The victim noticed the missing `.fr` TLD. Attackers register domains that mimic legitimate names but omit the country code (e.g., `assurance-maladie.com` or `noreply@assurance-maladie` without any TLD). Always verify the full domain.
Step‑by‑step command‑line validation (Linux / WSL / macOS):
1. Check domain registration and expiry whois wowitsmassive.com | grep -E "Creation Date|Registry Expiry" <ol> <li>Verify SPF, DKIM, DMARC records for the claimed domain (ameli.fr) dig ameli.fr TXT +short | grep spf dig ameli.fr TXT +short | grep dkim dig _dmarc.ameli.fr TXT +short</p></li> <li><p>See if the suspicious domain resolves to a known malicious IP nslookup wowitsmassive.com or using dig dig +short wowitsmassive.com</p></li> <li><p>Cross‑check against threat intelligence feeds (requires API key for some) curl -s "https://www.virustotal.com/api/v3/domains/wowitsmassive.com" -H "x-apikey: YOUR_KEY"
Windows (native):
Resolve-DnsName wowitsmassive.com WHOIS via PowerShell (install module first if needed) Find-Whois wowitsmassive.com Or use online tools: https://www.virustotal.com/gui/home/url
Phishing tell‑tales in DNS:
- Recently created domain (less than 30 days old).
- No SPF/DKIM records (legitimate healthcare providers always publish them).
- Domain registered via privacy service with suspicious registrar.
- Safe Analysis of Phishing URLs – Without Clicking the Trap
Never click suspicious links directly. Instead, use command‑line tools to inspect the destination without full rendering.
Step‑by‑step URL investigation:
1. Extract all URLs from an .eml file grep -oP 'https?://[^ ]+' suspicious_email.eml <ol> <li>Check redirect chain with curl (follows but stops at safe point) curl -L -I --max-redirs 5 "http://info.wowitsmassive.com/click.php?claim=123"</p></li> <li><p>Use urlscan.io API to get screenshots and DOM analysis curl -s "https://urlscan.io/api/v1/search/?q=domain:wowitsmassive.com" | jq .</p></li> <li><p>Test link in isolated environment (Firejail or Windows Sandbox) firejail --net=eth0 firefox "http://info.wowitsmassive.com"
Windows (PowerShell) safe investigation:
Invoke-WebRequest with maximum redirection but without executing scripts
$r = Invoke-WebRequest -Uri "http://info.wowitsmassive.com" -MaximumRedirection 0 -ErrorAction SilentlyContinue
$r.Headers.Location
Check SSL certificate issuer
[System.Net.ServicePointManager]::ServerCertificateValidationCallback = {$true}
If the URL points to a credential harvesting page (e.g., fake Ameli login), report it to Phishing Initiative or Google Safe Browsing.
- Incident Response for Suspected Phishing – What to Do After Spotting the Trap
You’ve identified a phishing email but already opened it (or even clicked). Immediate containment steps.
Step‑by‑step post‑click response:
- Disconnect from network (if you suspect drive‑by download):
Linux: `sudo ip link set wlan0 down` / Windows: `ipconfig /release` or toggle Airplane mode. - Check for anomalous processes (Linux):
ps aux --sort=-%mem | head -10 lsof -i -P -n | grep ESTABLISHED
- Windows (check active network connections and scheduled tasks):
netstat -an | findstr EST Get-ScheduledTask | Where-Object {$_.State -eq "Running"} - Clear cached credentials and browser cookies:
Linux: `rm -rf ~/.mozilla/firefox/.default-release/cookies.sqlite`
Windows: `Run` → `control` → Internet Options → Browsing history → Delete → Cookies.
– Reset any password entered into the fake page – assume credential theft.
– Report the phishing email:
Forward as attachment to `[email protected]` (French national reporting) or to the impersonated organization (Assurance Maladie: [email protected]).
– Enable MFA on all accounts that support it – this single action stops 99% of post‑phishing compromise.
- Building a Human Firewall – Training and Simulated Phishing Campaigns
Technology alone fails; user awareness must be reinforced regularly. The fact that a CTO almost fell for this attack proves that experts are also vulnerable when urgency overrides reason.
Recommended training modules (free/paid):
- Open‑source: Gophish (simulated phishing platform) – https://getgophish.com
- French government resources: “Cybermalveillance.gouv.fr” – includes phishing kits and awareness posters.
- Hands‑on lab (Linux): Set up a phishing simulation locally:
Clone Gophish and run wget https://github.com/gophish/gophish/releases/download/v0.12.1/gophish-v0.12.1-linux-64bit.zip unzip gophish-.zip && sudo ./gophish Access Web UI at https://localhost:3333 (default credentials: admin/gophish)
- Windows – using Atomic Red Team to test phishing detection:
Install-Module -Name AtomicTestHarnesses Invoke-AtomicTest T1566.001 -TestNames "Spearphishing Attachment"
Key metrics: Track “curiosity clicks” and “rapid reporting” using mail header analysis drills. The 20‑second rule (pause, inspect sender, expand headers) should become muscle memory.
7. Advanced: Using AI for Real‑Time Phishing Detection
Modern email gateways incorporate machine learning to detect anomalous sender behaviour. You can self‑host open‑source solutions.
Step‑by‑step deploy Rspamd (AI‑powered spam filter) on Linux:
sudo apt install rspamd redis-server
sudo systemctl enable rspamd
sudo rspamadm configwizard Auto‑train neural network
Add custom phishing rule for missing TLDs
echo 'MISSING_TLD = "/\bfrom:.assurance-maladie(?!.fr)/" {
score = 5.0;
description = "Missing .fr in sender domain";
}' | sudo tee /etc/rspamd/local.d/phishing.conf
sudo systemctl restart rspamd
Windows (Microsoft Defender for Office 365) – enable “Impersonation protection” for executive and well‑known brands. Use PowerShell to configure anti‑phishing policy:
Connect-ExchangeOnline New-AntiPhishPolicy -Name "FrenchHealthImpersonation" -EnableTargetedUserProtection $true -TargetedUsersToProtect "ameli.fr","assurance-maladie.fr"
Cloud hardening (Azure / AWS): Set up email flow rules to quarantine messages with mismatched From/Return-Path. Example Azure rule:
`Set-TransportRule -Identity “Phishing TLD check” -FromAddressMatchesPatterns “assurance-maladie” -HeaderMatchesMessageHeader Return-Path -HeaderMatchesPatterns “@(?!ameli\.fr)” -RejectMessageReasonText “Spoofed health domain”`
What Undercode Say:
- Key Takeaway 1: A missing TLD or mismatched Return-Path is a high‑confidence phishing indicator – never ignore it, even when the email appears urgent and contextually perfect.
- Key Takeaway 2: Client‑side countermeasures (blocking remote content by default) and instant header inspection provide a robust defense against the majority of modern social engineering attacks.
Analysis: The Assurance Maladie phishing attempt highlights how threat actors now mimic official communications without obvious spelling errors. The victim’s manual expansion of email headers is a low‑tech but highly effective technique that security tools sometimes miss. Organizations should enforce header inspection training and disable auto‑loading of external content across all devices. The open‑source tools mentioned (FairEmail, Evolution, Gophish, Rspamd) offer enterprise‑grade protection at zero cost – a critical advantage for SMEs and public sector entities.
Prediction:
By 2027, AI‑generated phishing emails will perfectly replicate brand voice, layout, and even dynamic personalisation (e.g., referencing your last doctor visit). As a result, traditional indicators like grammar and logos will become useless. The only remaining reliable signals will be cryptographic – DMARC enforcement at `p=reject` level, strict TLS, and user‑friendly header inspection built directly into mobile email clients. Expect regulatory pressure (EU’s NIS2, France’s LPM) to mandate automatic blocking of emails without valid SPF/DKIM alignment, effectively killing simple domain spoofing. Attackers will then pivot to compromising legitimate mailboxes inside the target’s supply chain – the next frontier of “zero‑indicator” phishing.
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IT/Security Reporter URL:
Reported By: Ines Wallon – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
