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In a sophisticated cyberattack, hackers exploited a vulnerability in Google’s OAuth system to send fraudulent emails that appeared to originate from [email protected]. These emails successfully bypassed DomainKeys Identified Mail (DKIM) authentication, tricking recipients into believing they were legitimate communications from Google.
The attackers directed victims to a fake “support portal” designed to harvest Google account credentials. Despite passing email authentication checks, the emails were part of a phishing campaign leveraging Google’s own infrastructure to enhance credibility.
More Details:
You Should Know: How to Detect and Mitigate DKIM Replay Attacks
1. Verify DKIM & SPF Manually
Use command-line tools to inspect email headers for DKIM and SPF validity:
Extract email headers (save as .eml file first) cat email.eml | grep -i "dkim-signature|received-spf" Check DKIM record (replace selector and domain) dig TXT selector._domainkey.example.com +short
2. Analyze Suspicious Links
Before clicking, inspect URLs with:
curl -sIL "https://suspicious-url.com" | grep -i "location|server"
3. Enable DMARC for Strict Enforcement
Add a DMARC DNS record (_dmarc.example.com) to enforce policies:
v=DMARC1; p=reject; rua=mailto:[email protected]; ruf=mailto:[email protected]; pct=100
4. Monitor OAuth Activity
Check authorized apps in Google Workspace:
Use GAM (Google Workspace Admin Tool) gam user <email> show oauthtokens
5. Simulate Phishing Attacks
Test defenses using tools like GoPhish:
Deploy GoPhish (Linux) sudo apt install golang -y git clone https://github.com/gophish/gophish.git cd gophish && go build ./gophish
What Undercode Say
This attack highlights the risks of over-relying on email authentication alone. Cybercriminals continuously evolve tactics, exploiting trusted platforms like Google. To defend against DKIM replay attacks:
– Enforce DMARC (p=reject) to block unauthorized senders.
– Train users to spot subtle inconsistencies (e.g., mismatched URLs).
– Audit OAuth permissions regularly using `gam` or Google’s API.
– Deploy endpoint detection (e.g., YARA rules for phishing emails):
rule Phishing_Google {
strings: $s = "[email protected]" nocase
condition: $s and not legitimate_dkim
}
Expected Output: A hardened email infrastructure with reduced phishing success rates.
Relevant URLs:
References:
Reported By: Phuong Nguyen – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
