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CISO Briefing: Gootloader’s “ZIP Trick”: Why It’s Bypassing Your EDR & Email Filters. A CISO’s Guide to Hunting This Threat. — by CyberDudeBivash

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

LinkedIn: ThreatWire cryptobivash.code.blog

FILELESS MALWARE • LNK/JS EXPLOIT • EDR BYPASS • THREAT HUNTING

Situation: The Gootloader malware campaign is back, and its primary TTP is *designed* to bypass your EDR (Endpoint Detection and Response). Attackers are using SEO Poisoning to target your employees, luring them to fake forum sites and tricking them into downloading a `.ZIP` file. This is not a “virus.” This is a “Trusted Process” Bypass.

This is a decision-grade CISO brief. The `.ZIP` file contains a malicious `.JS` (JavaScript) or `.LNK` (Shortcut) file. When your employee clicks it, it executes a *fileless*, in-memory PowerShell script using `wscript.exe`—a process your EDR is *whitelisted to trust*. This is the kill chain for ransomware and data exfiltration, and you are likely *already* vulnerable.

TL;DR — Gootloader’s “ZIP Trick” uses `.JS` files to run fileless malware via `wscript.exe`.

The TTP: SEO Poisoning → User downloads `document.zip` → User clicks `document.pdf.js` → `wscript.exe` (Trusted) → `powershell.exe -e …` (Fileless C2 Beacon).
The “EDR Bypass”: Your EDR is *whitelisted* to *trust* `wscript.exe`. It sees a “trusted” Microsoft process running and *ignores* it. This is a behavioral blind spot.
The Risk: This “backdoor” is the foothold for ransomware, corporate espionage, and PII data exfiltration.
THE ACTION (CISO): 1) HARDEN: *De-weaponize `.JS` files*. Change the default handler from `wscript.exe` to `notepad.exe` via GPO. 2) HUNT: This is the mandate. You *must* hunt for anomalous `wscript.exe` child processes and network traffic *now*.

TTP Factbox: Gootloader “ZIP Trick”

TTP	Component	Severity	Exploitability	Mitigation
SEO Poisoning (T1566)	Google Search Results	Critical	Bypasses SEG	User Training / MDR
Fileless Malware (T1059.007)	`.JS` File -> `wscript.exe`	Critical	EDR Bypass (LotL)	GPO Hardening / MDR

Fileless BackdoorEDR Bypass TTPLiving off the Land (LotL)Contents

Phase 1: The “Trusted” Trojan (Why the ZIP/LNK/JS TTP Kills EDR)

As a CISO, you’ve spent millions on a “Next-Gen” EDR (Endpoint Detection and Response) stack. Your vendor promised “AI-powered protection.” Yet, this attack bypasses it completely. Why?

It’s because this attack *never uses a “virus”*. It’s a “Living off the Land” (LotL) attack that exploits your EDR’s *trust*.

1. The SEO Poisoning (The “Bait”)

Your Secure Email Gateway (SEG) is useless. The attack doesn’t *start* with an email. It starts with your employee Googling a “benign” term:

“sample rental agreement template”
“employee performance review doc”
“free contract template”

The Gootloader gang *poisons* Google’s search results to make their *malicious website* (a fake forum) rank #1.

2. The “ZIP Trick” (The “Wrapper”)

The user, *trusting Google*, clicks the link. The fake forum says “Click here to download your document.” It delivers a `.ZIP` file. This is the “wrapper” to get the payload past any *network-level* scanners.

3. The “Trusted Process” (The “Bypass”)

The user opens the ZIP. Inside is a file: `agreement.pdf.js`.
Your employee, *not seeing the `.js` extension* (because Windows hides it by default), double-clicks.

This does *not* open Adobe Reader. It launches `wscript.exe` (Windows Script Host), a *legitimate, signed Microsoft tool*.

Your EDR *sees* `wscript.exe` running. It is *whitelisted* to trust this process. It *allows* it.
This is a *fileless attack*. The `.JS` script *never* drops a “malware.exe”. It runs *entirely in memory* inside the “trusted” `wscript.exe` process.

Phase 2: The “Fileless” Kill Chain (From Google to C2 Beacon)

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 Google Search)

Your employee, `user@yourcompany.com`, clicks a poisoned Google search result.

Stage 2: Execution (The `.JS` Click)

The user opens `document.zip` and double-clicks `document.pdf.js`. The `wscript.exe` process executes the in-memory script.

Stage 3: C2 & Persistence (The “EndClient” Backdoor)

The fileless `.JS` script (the “Gootloader” payload) does two things:

C2 Beacon: It spawns *another* trusted process, `powershell.exe -e …`, to make an *outbound HTTPS connection* to an attacker’s C2 server (a “C2 beacon”).
Persistence: It creates a new `Scheduled Task` or `Registry Run Key` to *re-launch* this same fileless script every time the user logs in.

The attacker now has a *persistent backdoor* on your employee’s machine. The breach is complete.

Stage 4: Post-Exploitation (The “Breach”)

The attacker uses this backdoor to:

Run Mimikatz *in-memory* to steal credentials.
Steal *all* browser session cookies (Session Hijacking) to bypass MFA.
Move laterally to your file servers and Domain Controller.
Exfiltrate your “4TB” of CUI, PII, and IP.
Deploy Ransomware.

Exploit Chain (Engineering)

This is a “Trusted Process” Hijack (T1219/T1059). The “exploit” is a *logic* flaw in your EDR Whitelisting policy.

Trigger: User double-clicks `.js` file.
Precondition: EDR/AV is configured to *automatically trust* all `wscript.exe` / `cscript.exe` processes. Windows “Hides known file extensions” is ON.
Sink (The RCE): `explorer.exe` → `wscript.exe file.js` → `powershell.exe -e …` (Fileless C2)
Module/Build: `wscript.exe` (Trusted), `powershell.exe` (Trusted).
Patch Delta: There is no “patch.” The “fix” is GPO Hardening (changing the default `.js` handler) and MDR (Threat Hunting).

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 file named `test.js`. 2) Put this *one line* of code in it: `WScript.CreateObject(“WScript.Shell”).Run(“calc.exe”);`
Execution: Double-click the `test.js` file.
Result: Did `calc.exe` launch? Did your EDR fire a P1 (Critical) alert for `wscript.exe -> calc.exe`? If it was *silent*, your EDR is *blind* to this TTP.
Safety Note: If `calc.exe` can run, so can a Cobalt Strike beacon.

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 Child Process.” This is your P1 alert. Your `wscript.exe` process should *NEVER* spawn a shell (`powershell.exe`, `cmd.exe`, `/bin/bash`).# EDR / SIEM Hunt Query (Pseudocode) SELECT * FROM process_events WHERE (parent_process_name = ‘wscript.exe’ OR parent_process_name = ‘cscript.exe’) AND (process_name = ‘powershell.exe’ OR process_name = ‘cmd.exe’)
Hunt TTP 2 (The C2): “Show me all *network connections* from `wscript.exe` or `cscript.exe` to a *newly-registered domain* or *anomalous IP*.”
Hunt TTP 3 (The Persistence): “Show me *all new* Scheduled Tasks or Registry Run Keys that contain `wscript.exe` or `cscript.exe`.”

Mitigation & Hardening (The CISO Mandate)

This is a Windows Configuration failure. This is the fix.

1. HARDEN (The *Real* Fix): This is your CISO mandate. De-weaponize JavaScript files.
You must *change the default file handler* for `.JS` files. An employee should *never* “execute” a `.JS` file. It should *open* in Notepad.
The Fix: Use GPO to change the default handler for `.js` files from `wscript.exe` (Execute) to `notepad.exe` (View). This *kills* the TTP.
2. HUNT (The “MDR” Fix): You *cannot* run a 9-to-5 SOC. 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.
3. VERIFY (The “Red Team” Fix): You *must* run an Adversary Simulation (Red Team) to *prove* your EDR and your SOC team *can* detect this TTP.

Audit Validation (Blue-Team)

Run this *today*. This is not a “patch”; it’s an *audit*.

# 1. Audit your EDR (The "Lab" Test)
# Run the "Lab Setup" test (`test.js -> calc.exe`). 
# Did your EDR *see* it? If not, it is BLIND.

# 2. Audit your File Handlers
# (Run `ftype JScript.file`)
# Does it say "wscript.exe"? If yes, you are VULNERABLE.
# Run the GPO to change it to "notepad.exe".

# 3. Run the "Lab Test" again
# Did `calc.exe` launch? Or did `notepad.exe` open?
# If Notepad opened, you have *successfully* hardened your fleet.

Is Your EDR Blind to “Fileless” Attacks?
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You need a layered defense. Here’s our vetted stack for this specific threat.

Kaspersky EDR
This is your *sensor*. It’s the #1 tool for providing the behavioral telemetry (process chains, network data) that your *human* MDR team needs to hunt.Edureka — Threat Hunting Training
Your SOC team can’t find what they don’t know. Train them *now* on PowerShell Threat Hunting and LotL TTPs.TurboVPN
The phish often lands on a *remote* device on *public Wi-Fi*. A VPN encrypts this initial access channel.

Alibaba Cloud (VDI)
A key mitigation. Use Virtual Desktop Infrastructure (VDI). If the VDI is popped, you *burn it* and re-image in seconds. The host is safe.AliExpress (Hardware Keys)
*Mandate* this for all Domain Admins. Get FIDO2/YubiKey-compatible keys. They stop the *initial phish* from succeeding.Rewardful
Run a bug bounty program. Pay white-hats to find flaws *before* APTs do.

CyberDudeBivash Services & Apps

We don’t just report on these threats. We hunt them. We are the “human-in-the-loop” that your automated EDR is missing.

Managed Detection & Response (MDR): This is the *solution*. Our 24/7 SOC team becomes your Threat Hunters, watching your EDR logs for these *exact* “wscript -> powershell” TTPs.
Adversary Simulation (Red Team): This is the *proof*. We will *simulate* this exact “Fileless” Gootloader kill chain to show you where you are blind.
Emergency Incident Response (IR): You found this TTP? Call us. Our 24/7 team will hunt the attacker and eradicate them.
PhishRadar AI — Stops the phishing attacks that *initiate* the breach.
SessionShield — Protects your *admin sessions* from the *credential theft* that happens after this breach.

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FAQ

Q: What is Gootloader?
A: Gootloader is a malware loader (a “dropper”). It’s the “first stage” of a breach. It uses SEO Poisoning to get onto a PC and then runs a fileless `.JS` or `.LNK` script to install a *real* backdoor (like a C2 beacon or ransomware).

Q: What is a LNK/JS exploit?
A: It’s not a “vulnerability” in LNK/JS files themselves, but a *technique*. It leverages a legitimate Windows function (shortcuts/scripts) to execute malicious code (like PowerShell) in a “fileless” way that evades simple antivirus.

Q: Why does my EDR/Antivirus miss this attack?
A: Because your EDR is *configured to trust* `wscript.exe` and `powershell.exe`. This is a “Trusted Process” bypass. The EDR sees a ‘trusted’ Microsoft process running and *ignores* it. You *must* have a *human* MDR team hunting for the *behavioral* anomalies.

Q: What is the #1 action to take *today*?
A: HARDEN. Go to your Group Policy (GPO) and *change the default file handler* for `.JS` and `.VBS` files from `wscript.exe` to `notepad.exe`. This *de-weaponizes* the TTP instantly. Your *second* action is to call our team to run an emergency Threat Hunt for this TTP.

Timeline & Credits

This “Gootloader” TTP (T1566.001 / T1059) is an active, ongoing campaign by multiple APTs and RaaS groups.
Credit: This analysis is based on active Incident Response engagements by the CyberDudeBivash threat hunting team.

References

Affiliate Disclosure: We may earn commissions from partner links at no extra cost to you. These are tools we use and trust. Opinions are independent.

CyberDudeBivash — Global Cybersecurity Apps, Services & Threat Intelligence.

cyberdudebivash.com · cyberbivash.blogspot.com · cryptobivash.code.blog

#Gootloader #LNKexploit #ZIP #FilelessMalware #PowerShell #EDRBypass #Ransomware #CyberDudeBivash #IncidentResponse #MDR #ThreatHunting #LotL #C2

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Gootloader’s “ZIP Trick”: Why It’s Bypassing Your EDR & Email Filters. A CISO’s Guide to Hunting This Threat.

CISO Briefing: Gootloader’s “ZIP Trick”: Why It’s Bypassing Your EDR & Email Filters. A CISO’s Guide to Hunting This Threat. — by CyberDudeBivash

Phase 1: The “Trusted” Trojan (Why the ZIP/LNK/JS TTP Kills EDR)

1. The SEO Poisoning (The “Bait”)

2. The “ZIP Trick” (The “Wrapper”)

3. The “Trusted Process” (The “Bypass”)

Phase 2: The “Fileless” Kill Chain (From Google to C2 Beacon)

Stage 1: Initial Access (The Google Search)

Stage 2: Execution (The `.JS` Click)

Stage 3: C2 & Persistence (The “EndClient” Backdoor)

Stage 4: Post-Exploitation (The “Breach”)

Exploit Chain (Engineering)

Reproduction & Lab Setup (Safe)

Detection & Hunting Playbook (The New SOC Mandate)

Mitigation & Hardening (The CISO Mandate)

Audit Validation (Blue-Team)

Recommended by CyberDudeBivash (Partner Links)

CyberDudeBivash Services & Apps

FAQ

Timeline & Credits

References

Leave a comment Cancel reply

Gootloader’s “ZIP Trick”: Why It’s Bypassing Your EDR & Email Filters. A CISO’s Guide to Hunting This Threat.

CISO Briefing: Gootloader’s “ZIP Trick”: Why It’s Bypassing Your EDR & Email Filters. A CISO’s Guide to Hunting This Threat. — by CyberDudeBivash

Phase 1: The “Trusted” Trojan (Why the ZIP/LNK/JS TTP Kills EDR)

1. The SEO Poisoning (The “Bait”)

2. The “ZIP Trick” (The “Wrapper”)

3. The “Trusted Process” (The “Bypass”)

Phase 2: The “Fileless” Kill Chain (From Google to C2 Beacon)

Stage 1: Initial Access (The Google Search)

Stage 2: Execution (The `.JS` Click)

Stage 3: C2 & Persistence (The “EndClient” Backdoor)

Stage 4: Post-Exploitation (The “Breach”)

Exploit Chain (Engineering)

Reproduction & Lab Setup (Safe)

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

Mitigation & Hardening (The CISO Mandate)

Audit Validation (Blue-Team)

Recommended by CyberDudeBivash (Partner Links)

CyberDudeBivash Services & Apps

FAQ

Timeline & Credits

References

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Detection & Hunting Playbook (The New SOC Mandate)