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Operation SkyCloak’s TTPs Are Coming For You: A CISO’s Guide to Defending Against LNK Exploits & Tor-Based Backdoors — by CyberDudeBivash

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

LinkedIn: ThreatWire cryptobivash.code.blog

APT ATTACK • LNK EXPLOIT • TOR C2 BACKDOOR • EDR BYPASS

Situation: A new APT (Advanced Persistent Threat) campaign, dubbed “Operation SkyCloak,” is actively bypassing “Next-Gen” security stacks. This is not a “smash and grab” ransomware attack; it is a sophisticated cyber-espionage campaign that combines two clever TTPs (Tactics, Techniques, and Procedures) to gain persistent, untraceable access to your network.

This is a decision-grade CISO brief. This attack *specifically* targets the blind spots in your EDR (Endpoint Detection and Response) and Zero-Trust policies. It uses “trusted” Windows processes (fileless LNK/PowerShell exploits) for initial access and “anonymized” networks (Tor-based C2 backdoors) for command and control. Your automated defenses are blind. This is a *human* threat that requires a *human-led* defense.

TL;DR — A new APT attack (“Operation SkyCloak”) is bypassing EDR and Firewalls.

TTP 1 (Initial Access): A spear-phishing email contains a malicious `.LNK` file (a “shortcut”) disguised as a document. When clicked, it runs a hidden, fileless PowerShell script.
TTP 2 (Persistence & C2): The script downloads and installs a legitimate (but modified) OpenSSH server and the Tor client.
TTP 3 (The Bypass): The SSH server is configured as a *hidden onion service*. This creates a persistent, anonymous, *outbound-only* backdoor that your firewall *cannot* block.
Why Defenses Fail: Your EDR is configured to *trust* `powershell.exe` and `ssh.exe` (Living off the Land). Your firewall is blind because it can’t block a single “bad IP” (Tor has thousands).
THE ACTION: 1) Harden (Block LNKs via email, use AppLocker to block `tor.exe`). 2) Hunt (This is the mandate. Hunt for anomalous `powershell.exe` child processes and *any* traffic to Tor nodes). 3) Respond.

Contents

Phase 1: The “LNK Exploit” (The “Fileless” Foothold)

The attack begins with a sophisticated spear-phishing email. The attachment is not a `.exe` or a `.docm`. It’s a `.LNK` file—a simple Windows shortcut. This is a clever EDR bypass technique for several reasons:

User Trust: The `.LNK` file is disguised with a legitimate-looking icon (e.g., a Word document or PDF). The user thinks they are opening a file named “Urgent_Communique.pdf”.
Signature Evasion: The `.LNK` file itself is not “malware.” It’s a legitimate Windows object. This allows it to bypass many static antivirus scanners that are looking for known-bad file hashes.
Fileless Execution: The *real* power is in the “Target” field of the shortcut. Instead of pointing to a program, the attacker points it to `powershell.exe` and passes a long, obfuscated command.
Example: `C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe -e JABj…[long base64 string]…`
The “Dropper”: When the user clicks the shortcut, they *run* this hidden PowerShell command. This is a “fileless” technique because the initial malicious script runs entirely in-memory. This script’s only job is to download the *real* payload (Stage 2) from a remote server and execute it.

Service Note: This is a classic Initial Access TTP. Your SEG (Secure Email Gateway) is your *only* automated chance to block this. If your filter can’t detect malicious LNKs or AI-generated phish, you’re exposed. Our PhishRadar AI is built to detect the *intent* of these attacks, not just their signatures.
Explore PhishRadar AI by CyberDudeBivash →

Phase 2: The “OpenSSH-Over-Tor” Backdoor (The Anonymous C2)

This is the most brilliant and dangerous part of “Operation SkyCloak.” The Stage 1 PowerShell script downloads and installs the Stage 2 payload: a modified copy of OpenSSH (the standard, trusted tool for secure remote access) and the Tor client.

This isn’t a “normal” RAT (Remote Access Trojan). This is a covert, persistent backdoor built from legitimate tools. This is a prime example of “Living off the Trusted Land” (LotL).

1. Why OpenSSH?

Attackers love OpenSSH because your security team *already trusts it*. Your EDR and firewall “allowlist” probably has a rule to permit `ssh.exe` and `sshd.exe` to run and communicate. The attacker installs their OpenSSH copy as a hidden Windows service, set to auto-start, ensuring their persistence.

2. Why Tor? (The “SkyCloak”)

This is the masterstroke for anonymity. The attacker configures the OpenSSH server to run as a **Tor Onion Service** (`.onion` address). This means:

No Inbound Firewall Holes: The SSH service doesn’t open a port on your firewall. It makes an *outbound-only* connection *to* the Tor network. This bypasses all inbound firewall rules.
Total Attacker Anonymity: The attacker connects to their `.onion` address to access the backdoor. Their *real* C2 IP address is completely obscured by the Tor network. They could be anywhere in the world.
No “Bad IP” to Block: Your threat intelligence feeds are useless. You can’t block the “attacker’s C2 IP” because there *isn’t one*. The C2 is a constantly moving target within the Tor network’s thousands of nodes.

The result is a fully encrypted, fully anonymous, persistent backdoor, running as a “trusted” service, that bypasses all but the most advanced network monitoring. This is a nation-state spy tool.

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

This entire kill chain is designed to defeat modern, “Next-Gen” security stacks. It attacks the *assumptions* your security is built on.

Your Firewall Assumes: “I only need to block *inbound* connections.”
The Bypass: This attack is *outbound-only*. The compromised host *initiates* the connection to the Tor network. Most firewalls are configured to allow all outbound HTTPS/443 traffic, which is exactly what Tor traffic can look like.
Your EDR Assumes: “I should trust `powershell.exe` and `ssh.exe`.”
The Bypass: This is a “Living off the Trusted Land” (LotL) attack. The EDR sees `explorer.exe` (the user) launch `powershell.exe` (admin tool). It then sees PowerShell launch `tor.exe` (legit app) and `ssh.exe` (legit app). A “lazy” EDR sees no “malware.exe” and generates no alert.
Your Threat Intel Assumes: “I can block known-bad C2 IPs.”
The Bypass: The C2 is a `.onion` address. There is no static IP to block.

The CISO Mandate: This is a “Human-in-the-Loop” problem.
Your 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 see `explorer.exe -> powershell.exe -> tor.exe -> sshd.exe` and we don’t call it “noise.” We call it “Operation SkyCloak” and initiate Incident Response in minutes.
Explore Our 24/7 MDR Service →

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

You cannot fight a layered attack with a single tool. You need a 3-layer defense: Harden, Hunt, and Verify.

1. HARDEN (The “Block”)

Stop the attack at Stage 1. Don’t let the LNK run.

Block LNKs: Configure your email gateway to *block* `.LNK` files (and `.zip` files containing them) entirely.
Harden PowerShell: Use Constrained Language Mode and enable script block logging and transcription.
Use AppLocker/WDAC: This is critical. Create a Windows Defender Application Control (WDAC) policy that *only* allows your *known, authorized* executables to run. This would block the attacker’s `tor.exe` and custom `ssh.exe` from *ever* launching.

2. HUNT (The “Mandate”)

This is the *new* mandate. You *must* assume they will get in. You need to find them. This requires a behavioral EDR and a 24/7 team to watch it.

Hunt TTP 1 (The Foothold): Alert on `explorer.exe` (or `outlook.exe`) spawning `powershell.exe -e` (obfuscated). This is a P1 alert.
Hunt TTP 2 (The C2): This is your #1 signal. Block and alert on *all* outbound connections to known Tor entry nodes. No corporate workstation or server should *ever* be connecting to Tor.
Hunt TTP 3 (The Persistence): Alert on *any* new Windows service creation, especially one with a suspicious name or path (e.g., `ssh.exe` running from `C:\Users\…\AppData\`).

3. VERIFY (The “Red Team”)

You have hardened. You are hunting. Does it *work*? You *must* assume it doesn’t.
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. *Try* to bypass our EDR. *Try* to use a Tor C2. Show us where we are blind.”

This is not a theoretical exercise.
Our CyberDudeBivash Red Team will *be* “Operation SkyCloak.” 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 defenses.
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
Train your SecOps team *now* on PowerShell Hardening, Threat Hunting, and Incident Response TTPs.TurboVPN
Your *legitimate* admin access (RDP/SSH) should *only* be over a trusted, encrypted VPN, not the public internet.

Alibaba Cloud (VPC/SEG)
This is *how* you build the “Firewall Jails” (Network Segmentation) to contain the blast radius of a breach.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 -> Tor” 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 Tor traffic? 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 Services Book 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: How do I block Tor on my network?
A: The best way is at your firewall/proxy. Maintain an updated blocklist of all known Tor entry node IPs. A better, more robust way is to use an EDR (like Kaspersky) that can identify Tor traffic *behaviorally* (via its “JA3/JARM” fingerprint) and block the *process* on the endpoint, regardless of the IP.

Q: My EDR is “Next-Gen AI”. Am I safe?
A: No. Not automatically. Your AI is only as good as its configuration. If it’s configured to “trust” PowerShell and “ignore” SSH, it will miss this. This attack is designed to look like “noise.” It takes a 24/7 human MDR team (like ours) to analyze that “noise” and identify it as an APT.

Q: I found Tor traffic! What do I do?
A: Call our IR team. NOW. Do not just “block the IP.” Do not “turn off the machine.” You are in a *live breach* with a sophisticated APT. Isolate the host from the network immediately and begin digital forensics.

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