Threat Hunting for Data Exfiltration: Uncovering Obscure File Hosting Domains

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Introduction

Data exfiltration remains a critical concern for cybersecurity teams, with threat actors and insider threats leveraging obscure file-hosting domains to bypass detection. This article explores a curated list of 70+ lesser-known file-sharing domains and provides actionable techniques to hunt for suspicious activity in your network.

Learning Objectives

  • Identify uncommon file-hosting domains used in data exfiltration.
  • Leverage EDR and firewall logs to detect suspicious file transfers.
  • Utilize open-source threat intelligence to track attacker methodologies.

You Should Know

1. Detecting Suspicious File Transfers via Firewall Logs

Command (Splunk Query):

index=firewall (dest_host="tempsend.com" OR dest_host="sendgb.com") | stats count by src_ip, dest_host, url

Step-by-Step Guide:

  • This query searches firewall logs for connections to known file-sharing domains.
  • Modify `dest_host` values to include additional domains from the provided list.
  • Correlate results with user activity to identify potential exfiltration attempts.

2. Hunting for Malicious Downloads in EDR

Command (Windows PowerShell):

Get-WinEvent -LogName "Microsoft-Windows-Sysmon/Operational" | Where-Object { $_.Message -match "tempsend.com|sendgb.com" } | Select-Object TimeCreated, Message

Step-by-Step Guide:

  • Sysmon logs can reveal file downloads from suspicious domains.
  • Adjust the regex pattern to include other high-risk domains.
  • Investigate any matches for unauthorized data transfers.

3. Blocking High-Risk Domains via DNS Filtering

Command (Linux iptables):

sudo iptables -A OUTPUT -p tcp -d tempsend.com -j DROP 
sudo iptables -A OUTPUT -p tcp -d sendgb.com -j DROP

Step-by-Step Guide:

  • Use `iptables` to block outbound traffic to known malicious domains.
  • Maintain a dynamic blocklist updated with new domains from threat intel feeds.

4. Automating Domain Monitoring with Python

Python Script Snippet:

import requests 
blocklist = ["tempsend.com", "sendgb.com"] 
for domain in blocklist: 
response = requests.get(f"http://{domain}") 
if response.status_code == 200: 
print(f"Active domain: {domain}")

Step-by-Step Guide:

  • This script checks if domains are reachable, indicating potential adversary use.
  • Integrate with SIEM for real-time alerts.

5. Leveraging LOLBAS for Living-off-the-Land Attacks

Resource: LOLOL.farm

Step-by-Step Guide:

  • Monitor this repository for updates on attacker techniques.
  • Cross-reference with internal logs for suspicious binaries (e.g., `certutil.exe` downloading files).

What Undercode Say

  • Key Takeaway 1: Obscure file-sharing domains are a growing exfiltration vector—proactive blocking and logging are essential.
  • Key Takeaway 2: Combining firewall, EDR, and threat intelligence maximizes detection coverage.

Analysis:

Threat actors increasingly abuse lesser-known platforms to evade traditional security tools. By maintaining an updated blocklist and automating log analysis, defenders can reduce dwell time and mitigate data breaches. The integration of open-source resources like LOLOL.farm further enhances visibility into evolving attacker tradecraft.

Prediction

As defenders block mainstream file-sharing sites, adversaries will shift to decentralized or ephemeral hosting solutions. Future attacks may leverage blockchain-based storage or encrypted peer-to-peer networks, requiring advanced behavioral analytics for detection.

IT/Security Reporter URL:

Reported By: Dimitris Binichakis – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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