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CISO Briefing: "Fake" Extensions on the Official Marketplace Are Holding Files Hostage. (Your EDR is Blind. Check Your PC NOW). — by CyberDudeBivash

By CyberDudeBivash · 01 Nov 2025 · cyberdudebivash.com · Intel on cyberbivash.blogspot.com

This is a decision-grade CISO brief. This is a PostMortem of a "Trusted Process" bypass. The malicious extension runs *inside* your trusted `chrome.exe` process, stealing *all* passwords and active session cookies (MFA Bypass). We are providing the *only* playbook for securing your development fleet and protecting your financial and intellectual property.

Contents

1. Phase 1: The "Trusted Process" Bypass (Why Your EDR Fails)
2. Phase 2: The "Hostage" Kill Chain (Check Your PC NOW)
3. Exploit Chain (Engineering)
4. Reproduction & Lab Setup (Safe)
5. Detection & Hunting Playbook (The *New* SOC Mandate)
6. Mitigation & Hardening (The CISO's 3-Step Plan)
7. Audit Validation (Blue-Team / *User Guide*)
8. Tools We Recommend (Partner Links)
9. CyberDudeBivash Services & Apps
10. FAQ
11. Timeline & Credits
12. References

Phase 1: The "Trusted Process" Bypass (Why Your EDR Fails)

As a CISO, your EDR (Endpoint Detection and Response) tool is based on *trusting* digitally signed binaries. You *have* to trust `chrome.exe` and `vscode.exe`.

Attackers exploit this trust. This is the "Trusted Process" Hijack. The attacker *doesn't* need to hack your firewall. They just need your employee to *install a malicious extension* from the Chrome Web Store (or an unvetted marketplace like **Open VSX**).

1. The Typosquatting Trap

The attacker registers a *fake* extension with a *similar name* to a popular tool (e.g., "Color Picker" vs. "Color Pickr"). This is **Typosquatting** on the extension marketplace.

2. The "Hostage" Payload

The user installs the fake extension. It runs *inside* your trusted browser process. The extension's malicious code (e.g., `background.js`) does *not* look for viruses. It looks for *your credentials*.

• `chrome.cookies.get()` (Steals active session tokens).
• `chrome.passwords.get()` (Steals saved passwords).

Your EDR sees "normal" `chrome.exe` activity. It sees the browser making an *HTTPS POST* request to the attacker's C2 server. This is the LotL (Living off the Land) attack—the attacker is *hiding their malicious activity inside a trusted process*.

Phase 2: The "Hostage" Kill Chain (Check Your PC NOW)

This is the full ransomware and espionage kill chain that our Incident Response (IR) teams are seeing in the wild.

Stage 1: Initial Access (The Download)

Your developer Googles "JS formatter" and clicks the *malicious* extension on the marketplace.

Stage 2: Execution & Collection (The Infostealer)

The user installs the extension. It runs *inside* `vscode.exe` or `chrome.exe`. It *instantly* steals your M365 session cookie (MFA Bypass) and all your saved passwords/cards.

Stage 3: C2 & Data Exfiltration (The "Hostage" TTP)

The attacker logs into your M365 account (via Session Hijacking). They *download* your 4TB of "crown jewel" PII/IP data. They exfiltrate it.

The final "ransom" is *not* an encrypted file. It's an *email* to your CEO: **"We have 4.3 million customer records and your GitHub master key. Pay X amount, or we leak it."** Your data is now being held *hostage*.

Exploit Chain (Engineering)

This is a "Trusted Process" Hijack (T1219/T1176). The "exploit" is a *logic* flaw in your EDR Whitelisting policy.

• Trigger: User installs Extension with `tabs` and `cookies` read permission.
• Precondition: EDR *whitelists* `chrome.exe` / `vscode.exe` / `node.exe` traffic.
• Sink (The Breach): Malicious JS `background.js` uses `fetch()` or `XMLHTTPRequest` to `POST` stolen cookies to C2.
• Module/Build: `chrome.exe` (Trusted) → `HTTPS POST` to `attacker-c2.com`.
• Patch Delta: There is no "patch." The "fix" is MDR (Hunting) + Session Monitoring.

Reproduction & Lab Setup (Safe)

You *must* test your EDR's visibility for this TTP.

• Harness/Target: A sandboxed Windows 11 VM with your standard EDR agent installed.
• Test: 1) Create a simple "unpacked" extension that reads cookies. 2) Load it manually. 3) Have it `fetch()` (POST) this data to a C2 you control (e.g., a "webhook.site" URL).
• Result: Did your EDR/DLP fire a P1 (Critical) alert for data exfiltration? Or was it *silent*? If it was silent, *your EDR is blind* to this TTP.

Detection & Hunting Playbook (The *New* SOC Mandate)

Your SOC *must* hunt for this. Your SIEM/EDR is blind to the exploit itself; it can *only* see the *result*. This is your playbook.

• Hunt TTP 1 (The #1 IOC): "Anomalous Session." This is your P1 alert. Hunt your *cloud* logs (M365, AWS, Salesforce) for "Impossible Travel". This is what our SessionShield app automates.
• Hunt TTP 2 (The C2): "Show me all *network connections* from `chrome.exe` or `vscode.exe` to a *newly-registered domain* or *anomalous IP*." (The Infostealer C2).
• Hunt TTP 3 (The Exfil): "Show me a *single user* downloading > 1GB of data from SharePoint or GitHub." This is *anomalous behavior*.

Mitigation & Hardening (The CISO's 3-Step Plan)

This is a DevSecOps and Zero-Trust failure. This is the fix.

• 1. PROTECT (The "Session"): You *must* assume the token *will* be stolen.
  • Phish-Proof MFA (FIDO2): Hardware Keys (FIDO2) *token-bind* the session, making the stolen cookie *useless*. This is the #1 fix.
  • Session Monitoring: Deploy SessionShield. It's the *only* tool that *behaviorally* detects the *anomalous use* of that stolen session and *kills it*.
• 2. HARDEN (The "Policy"):
  • **Allowlist Extensions:** Use GPO/MDM to *block* all extensions *except* for a *pre-vetted* "corporate allowlist."
  • **Stop Browser Passwords:** *Mandate* Password Managers (like Kaspersky's). *Starve* the infostealer.
• 3. HUNT (The "Guard"): You *must* have a 24/7 human-led MDR team (like ours) to hunt for the *behavioral* TTPs (like Hunt TTP 1) that your EDR will log but *not* alert on.

Audit Validation (Blue-Team / *User Guide*)

Run this *today*. This is not a "patch"; it's an *audit*.

How to Check Your Browser (Chrome/Edge):

1. Type `chrome://extensions` (for Chrome) or `edge://extensions` (for Edge) in your address bar.
2. AUDIT THE LIST: Do you *know* and *trust* 100% of these?
3. CHECK PERMISSIONS: Click "Details" on each one. Does your "Pretty Theme" *really* need "Read and change all your data on all websites"? **If yes, REMOVE IT. It is a spy.**

Recommended by CyberDudeBivash (Partner Links)

You need a layered defense. Here's our vetted stack for this specific threat.

CyberDudeBivash Services & Apps

FAQ

Q: What is a Malicious Browser Extension?
A: It's a "Trojan Horse" that you *willingly* install. It looks like a "Theme" or "Productivity" tool, but it contains malicious code (e.g., `background.js`) that runs *inside* your trusted browser, giving it full access to all your passwords, cookies, and data.

Q: Why doesn't my EDR or Antivirus miss this attack?
A: Because your EDR is *configured to trust* `chrome.exe` and `vscode.exe`. This is a "Trusted Process" bypass. The malicious code runs *in the memory* of this trusted process. Your EDR has no "bad file" to scan and sees "normal" behavior (a browser connecting to the internet).

Q: How do I check my extensions *right now*?
A: In Chrome/Edge, type `chrome://extensions` in your address bar. *Audit the permissions*. Does your "Theme" extension *really* need "Read all data on all websites"? If yes, **REMOVE IT.**

Q: What is the #1 fix for this *entire class* of attack?
A: Phish-Proof MFA (Hardware Keys). This TTP's *goal* is Session Hijacking to bypass MFA. Hardware Keys (FIDO2) use "token-binding," which makes the stolen cookie *cryptographically useless* to the attacker.

Timeline & Credits

This "Malicious Extension" TTP is an active, ongoing campaign by multiple APTs. The "Open VSX" vector is a *new* supply chain risk for developers.
Credit: This analysis is based on active Incident Response engagements by the CyberDudeBivash threat hunting team.

References

• MITRE ATT&CK: T1176 (Browser Extensions)
• MITRE ATT&CK: T1539 (Session Hijacking)
• CyberDudeBivash: SessionShield - The Session Hijacking Defense

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