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CISO Briefing: How to Detect the “EndClient” RAT: A Step-by-Step Hunt Guide for a Threat Your AV Will Miss (IOCs Included) — by CyberDudeBivash

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

LinkedIn: ThreatWire cryptobivash.code.blog

FILELESS MALWARE • LNK EXPLOIT • EDR BYPASS • THREAT HUNTING

Situation: This is a CISO-level threat warning. A new fileless RAT (Remote Access Trojan), dubbed “EndClient”, is bypassing traditional AV (Antivirus) and “Next-Gen” EDR (Endpoint Detection and Response). 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.

TTP Factbox: “EndClient” Fileless RAT

TTP	Component	Severity	Exploitability	Mitigation
Phishing (T1566.001)	`.LNK` in `.ZIP` Attachment	Critical	SEG Bypass	PhishRadar AI / Filter Rules
Fileless Malware (T1059.001)	`powershell.exe -e …`	Critical	EDR Bypass (LotL)	MDR (Threat Hunting)

Fileless BackdoorEDR Bypass TTPLiving off the Land (LotL)Contents

Phase 1: The “Trusted” Trojan (Why the ZIP/LNK 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 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 “EndClient” Backdoor)

The fileless PowerShell script (the “EndClient” RAT) does two things:

C2 Beacon: It makes an *outbound HTTPS connection* to an attacker-controlled server (a “C2 beacon”), often using DNS-over-HTTPS (DoH) to bypass firewalls.
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 clicks a malicious LNK or Phish.
Precondition: EDR/AV is configured to *automatically trust* all `powershell.exe` processes. Email gateway *allows* `.LNK` files inside `.ZIPs`.
Sink (The RCE): `explorer.exe` → `file.lnk` → `powershell.exe -e …` (Fileless C2)
Module/Build: `powershell.exe` (Trusted) → `HTTPS POST` to `attacker-c2.com`.
Patch Delta: There is no “patch.” The “fix” is Application Control (WDAC) 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 `.LNK` file. 2) In “Target”, set: `powershell.exe -c “calc.exe”`.
Execution: Double-click the `.LNK` file.
Result: Did `calc.exe` launch? Did your EDR fire a P1 (Critical) alert? If it was *silent*, your EDR is *blind* to this TTP.
Safety Note: If `calc.exe` can run, so can the “EndClient” RAT.

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 EDR (like Kaspersky) must be tuned for this.# EDR / SIEM Hunt Query (Pseudocode) SELECT * FROM process_events WHERE (parent_process_name = ‘explorer.exe’ OR parent_process_name = ‘outlook.exe’ OR parent_process_name = ‘winword.exe’) AND (process_name = ‘powershell.exe’ OR process_name = ‘cmd.exe’ OR process_name = ‘cscript.exe’) AND (command_line CONTAINS ‘-e’ OR command_line CONTAINS ‘-enc’)
Hunt TTP 2 (The C2): “Show me all *network connections* from `powershell.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 `powershell.exe -e …`”

Mitigation & Hardening (The CISO Mandate)

This is a DevSecOps failure. This is the fix.

1. HARDEN (The “Block”):
- 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.
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 (LNK -> calc.exe). 
# Did your EDR *see* it? If not, it is BLIND.

# 2. Audit your Logs (The "Hunt")
# Run the "Hunt TTP 1" query *now*.
# Did you find `powershell.exe -e`? If "yes," you are breached.

If your EDR is *blind*, call our team.

Is Your EDR Blind to “Fileless” Attacks?
Your SOC is slow. Your EDR is whitelisted. CyberDudeBivash is the leader in Ransomware Defense. We are offering a Free 30-Minute Ransomware Readiness Assessment to show you the *exact* gaps in your “LotL” and “Fileless” defenses.

Book Your FREE 30-Min Assessment Now →

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 “Fileless” 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 initial spear-phishing email that delivers the Stage 1 LNK foothold.
SessionShield — Protects your *admin sessions* from the *credential theft* that happens after this breach.

Book Your FREE 30-Min Assessment Explore 24/7 MDR Services 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*.

Timeline & Credits

This “LNK-in-ZIP” TTP (T1566.001) is an active, ongoing campaign by multiple APTs.
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

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

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How to Detect the “EndClient” RAT: A Step-by-Step Hunt Guide for a Threat Your AV Will Miss (IOCs Included)

CISO Briefing: How to Detect the “EndClient” RAT: A Step-by-Step Hunt Guide for a Threat Your AV Will Miss (IOCs Included) — by CyberDudeBivash

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

1. The ZIP File (The “Wrapper”)

2. The LNK File (The “Trigger”)

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

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

Stage 1: Initial Access (The Phish)

Stage 2: Execution (The LNK 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

How to Detect the “EndClient” RAT: A Step-by-Step Hunt Guide for a Threat Your AV Will Miss (IOCs Included)

CISO Briefing: How to Detect the “EndClient” RAT: A Step-by-Step Hunt Guide for a Threat Your AV Will Miss (IOCs Included) — by CyberDudeBivash

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

1. The ZIP File (The “Wrapper”)

2. The LNK File (The “Trigger”)

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

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

Stage 1: Initial Access (The Phish)

Stage 2: Execution (The LNK 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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Leave a comment Cancel reply

Detection & Hunting Playbook (The New SOC Mandate)