Author: CyberDudeBivash
Powered by: CyberDudeBivash Brand | cyberdudebivash.com
Related:cyberbivash.blogspot.com

CISO Briefing: Hackers Are Hiding “Fileless” Backdoors in ZIP Files. Your EDR is Blind. (Are You Infected?) — by CyberDudeBivash

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

LinkedIn: ThreatWirecryptobivash.code.blog

FILELESS MALWARE • LNK EXPLOIT • EDR BYPASS • THREAT HUNTING

Situation: This is a CISO-level threat warning. Attackers are weaponizing `.ZIP` files to deliver fileless backdoors that your EDR (Endpoint Detection and Response) and Antivirus are *not* detecting. This is not a “virus.” This is an EDR bypass TTP (Tactic, Technique, and Procedure).

This is a decision-grade CISO brief. The TTP is simple: A `.ZIP` file (which your email filter allows) contains a malicious `.LNK` (shortcut) file. This LNK file executes an *in-memory* PowerShell script, which is a fileless backdoor. Your EDR is blind because it’s configured to *trust* `powershell.exe`. This is the kill chain for ransomware and data exfiltration, and you are likely *already* vulnerable.

TL;DR — Attackers are hiding malware in `.LNK` files inside `.ZIP` files to bypass EDR.

• The Threat: “Living off the Land” (LotL) attack. The ZIP is just a wrapper to bypass email filters.
• The TTP: `ZIP` → `Malicious .LNK` → `powershell.exe -e [base64_string]` → Fileless C2 Beacon.
• Why Defenses Fail: Your AV/EDR is whitelisted to *trust* `powershell.exe`. It sees a “trusted” Microsoft process making a network connection 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: 1) HARDEN: Block `.LNK`, `.VBS`, `.HTA` files inside ZIPs at your email gateway. 2) HUNT: This is the mandate. You *must* hunt for anomalous `powershell.exe` child processes and network traffic. 3) VERIFY: Run a Red Team engagement to *prove* your EDR can (or can’t) see this.

Contents

1. Phase 1: The “Trusted” Trojan (Why the ZIP/LNK TTP Kills EDR)
2. Phase 2: The “Fileless” Kill Chain (From Click to C2 Beacon)
3. Phase 3: PostMortem – Why Your EDR & SIEM Are Blind
4. The CISO’s 3-Step “Harden, Hunt, Verify” Defense Plan
5. Tools We Recommend (Partner Links)
6. CyberDudeBivash Services & Apps
7. FAQ

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

As a CISO, you’ve spent millions on a “Next-Gen” Endpoint Detection and Response (EDR) 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 ZIP File (The “Wrapper”)

Your Secure Email Gateway (SEG) is configured to block `.exe`, `.dll`, and `.ps1` files. But it *must* allow `.zip` files for legitimate business. The attacker knows this. The ZIP file is just a “Trojan Horse” wrapper to get the *real* payload past your email scanner.

2. The LNK File (The “Trigger”)

Inside the ZIP is a `.LNK` (Windows Shortcut) file. Your EDR’s *static scanner* (Antivirus) checks this file. It finds *no malware signature*. Why? Because a `.LNK` file *isn’t malware*. It’s a legitimate Windows file. This is Signature Evasion.

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

The `.LNK` file’s “Target” field is the weapon. It’s a command like:
`C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe -e JAB…[long_base64_string]…`
When the user clicks the LNK (disguised as “Invoice.pdf”), your EDR sees `powershell.exe` (a *trusted, signed Microsoft tool*) being launched. It *allows* this. The `-e` flag tells PowerShell to run an *encoded* script *directly in memory*.
This is a *fileless attack*. No “malware.exe” is *ever* written to disk. Your EDR, configured to “trust” PowerShell, is now 100% blind to the malicious code running inside it.

Phase 2: The “Fileless” Kill Chain (From Click 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 Phish)

An attacker uses AI-powered spear-phishing to send a hyper-realistic email to your finance department. “Urgent: Attached is the overdue invoice [Ref: 883-A].zip.”
(This is where our PhishRadar AI provides its first line of defense, detecting the *intent* of the phish.)

Stage 2: Execution (The LNK Click)

The employee, under pressure, opens the ZIP and double-clicks what they think is an invoice. The malicious `.LNK` file executes the *in-memory PowerShell script*.

Stage 3: C2 & Persistence (The Backdoor)

The fileless PowerShell script does two things:

1. C2 Beacon: It makes an *outbound HTTPS connection* to an attacker-controlled server (a “C2 beacon”). Your firewall *allows* this, as it looks like “normal” web traffic from a “trusted” process.
2. 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. The “are you infected?” in the headline is now “yes.”

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.

Phase 3: PostMortem – Why Your EDR & SIEM Are Blind

This TTP is a “CISO PostMortem” because it highlights a *fundamental failure* in automated, “out-of-the-box” security stacks.

Your SIEM is blind. It *might* log the event, but it’s one `powershell.exe` launch among 100,000. It’s “noise.” It’s not a “P1 alert.”

Your EDR is blind. It is *whitelisted* to trust `powershell.exe`. It is *whitelisted* to trust `explorer.exe`. It *sees* the process chain (`explorer.exe` -> `powershell.exe`) and flags it as “benign admin activity.”

Your *entire* multi-million dollar security stack is defeated by one `.LNK` file because your defense is built on *signatures*, not *behavior*. You are looking for “known-bad” files, while the attacker is using “known-good” tools in a “known-bad” *way*.

The CISO Mandate: You MUST have a 24/7 MDR.
An automated EDR is just a “noise generator.” You need a Managed Detection & Response (MDR) service. Our 24/7 CyberDudeBivash SecOps team is trained to hunt for *these specific TTPs*.

We don’t see “noise.” We see a “Priority 1 Incident.” Our hunt query is: “Why is `powershell.exe` being spawned by `explorer.exe` with an *encoded command*? And why is it *making a network connection* to a *newly-registered domain*?”

We see this, identify it as a C2 beacon, and initiate Incident Response in *minutes*, not months.
Explore Our 24/7 MDR Service →

The CISO’s 3-Step “Harden, Hunt, Verify” Defense Plan

You cannot patch this. This is a *TTP*, not a CVE. You must adapt your *strategy*.

1. HARDEN (The “Block”)

This is your most powerful *preventative* control.

• Email Gateway: Configure your email filter to *block* `.ZIP` files that contain `.LNK`, `.VBS`, `.HTA`, or `.JS` files. This is non-negotiable.
• Endpoint Hardening: Use Windows Defender Application Control (WDAC) or AppLocker to *block* `powershell.exe` from running *at all* for standard users.
• PowerShell Hardening: If you can’t block it, *harden* it. Enforce PowerShell Constrained Language Mode via GPO and *turn on* Script Block Logging.

2. HUNT (The “Mandate”)

You *must* assume they are already inside. Your *only* defense is to find them. This is the *new* SOC mandate. You *must* be hunting for this TTP *right now*.

• Hunt Query #1 (The TTP): “Show me *all* child processes of `powershell.exe -e` (obfuscated) or `cscript.exe`.”
• Hunt Query #2 (The C2): “Show me *all* network connections from *any* process *except a browser* (`chrome.exe`, `msedge.exe`) to a *newly-registered domain*.”
• Hunt Query #3 (The Persistence): “Show me *all new* Scheduled Tasks or Registry Run Keys that contain `powershell.exe`.”

3. VERIFY (The “Red Team”)

You have hardened. You are hunting. Does it *work*?
You need to *test* your stack. This is the job of an Adversary Simulation (Red Team). You hire a team of ethical hackers (like us) and give them one command: “Breach us. *Use* a malicious LNK in a ZIP. *Try* to bypass our EDR. Show us where we are blind.”

This is not a theoretical exercise.
Our CyberDudeBivash Red Team will *be* this APT. We will *show* you this exact kill chain in a controlled environment. This is the *only* way to get real-world proof of your risk and justify the budget for your (Pillar 2) MDR team.
Book an Adversary Simulation (Red Team) →

Recommended by CyberDudeBivash (Partner Links)

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* “LNK -> PowerShell” TTPs.
• Adversary Simulation (Red Team): This is the *proof*. We will simulate this *exact* EDR bypass kill chain to show you where you are blind.
• Emergency Incident Response (IR): You see this TTP? You call us. Our 24/7 team will hunt the attacker and eradicate them.
• PhishRadar AI — Stops the initial spear-phishing email that delivers the Stage 1 LNK foothold.
• SessionShield — Protects your *admin* sessions, so even if the attacker gets `SYSTEM`, we detect their anomalous *session* behavior.

Explore 24/7 MDR ServicesBook an Adversary Simulation (Red Team)Subscribe to ThreatWire

FAQ

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

Q: What is “Fileless Malware”?
A: It’s a type of malicious software that runs *entirely in memory (RAM)*. It never writes a “malware.exe” file to the hard drive. Because most antivirus (AV) is built to *scan files*, this attack is invisible to them.

Q: My EDR has “AI.” Am I safe?
A: No. Not automatically. Your AI is only as good as its configuration. If it’s configured to “trust all signed Microsoft processes” (like `powershell.exe`), it will *miss this*. This attack is designed to *exploit* that trust. You *must* have a *human* MDR team hunting for the *behavioral* anomalies.

Q: I found this TTP! What do I do?
A: 1. Isolate the host(s) immediately. 2. Do not turn it off (you will destroy the in-memory evidence). 3. Call our 24/7 Incident Response hotline. We need to perform memory forensics, find the persistence mechanism, and hunt for *lateral movement*.

Next Reads

• [Related Post: The 5 “Fileless” Attack TTPs Your EDR is Missing]
• Daily CVEs & Threat Intel — CyberBivash
• CyberDudeBivash Apps & Services Hub

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

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