URGENT PATCH ALERT • CVE-2025-77801

URGENT PATCH: Critical QNAP NetBak Replicator Flaw Allows Remote Code Execution (RCE)

By CyberDudeBivash • October 06, 2025 • Urgent Security Directive

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Disclosure: This is a security advisory for QNAP users. It contains affiliate links to relevant security solutions. Your support helps fund our independent research.

Emergency Guide: Table of Contents

Chapter 1: The Hidden Threat — When Your Backup Software is the Backdoor

This is an urgent security alert for all QNAP users who use the NetBak Replicator software on their Windows PCs. A critical Remote Code Execution (RCE) vulnerability, tracked as **CVE-2025-77801**, has been discovered and is being actively exploited. This is not a flaw on your NAS device itself, but in the client software on your computer. Backup software is highly privileged and trusted, making a vulnerability in it extremely dangerous. An attacker can exploit this flaw to take complete control of your Windows PC.

Chapter 2: Threat Analysis — The Man-in-the-Middle RCE (CVE-2025-77801)

The vulnerability is a classic and severe flaw in the software’s update process.

The Exploit:

Insecure Update Check:** The NetBak Replicator software checks for new versions by making a request over an unencrypted channel (HTTP) instead of a secure one (HTTPS).
**Man-in-the-Middle (MitM) Attack:** An attacker on the same network as the victim (e.g., on the same public Wi-Fi, or an attacker who has already compromised another device on the network) can intercept this unencrypted update request.
**Malicious Response:** The attacker responds to the update request with their own malicious file, pretending to be a legitimate update from QNAP.
**RCE:** The NetBak Replicator software, trusting the response, downloads and executes the attacker’s malicious file. Because backup software often runs with high privileges, this gives the attacker immediate, full control over the Windows PC.

Chapter 3: The Defender’s Playbook — A Step-by-Step Patching Guide

You must manually update the software on every Windows computer that has NetBak Replicator installed.

Step 1: Identify All Affected PCs

First, identify all computers in your home or business that are running the QNAP NetBak Replicator software.

Step 2: Download the Official Patch

Go to the official QNAP website’s support and download section. Navigate to the “Utilities” area and download the latest available version of NetBak Replicator for Windows. **Do not download this software from any other source.**

Step 3: Install the Update on Every PC

Run the installer you just downloaded on every single PC that has the old version. This will replace the vulnerable software with the new, secure version that performs its update checks over HTTPS.

Chapter 4: The Strategic Lesson — Securing Client-Side Applications

This incident is a critical reminder that securing your data is an ecosystem problem. It is not enough to simply secure your server (the NAS). You must also secure every single client-side application that connects to it. In this case, even a fully patched and hardened QNAP NAS would be of no help if the user’s PC was compromised via the vulnerable backup client.

A holistic security strategy requires you to manage the security posture of both your servers and your endpoints with equal rigor.

Protect the Endpoint: Your first and last line of defense is a powerful security suite on your endpoint. **Kaspersky’s security solutions** can provide a critical safety net by detecting the malicious payload, even if the delivery mechanism is a trusted application.

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About the Author

CyberDudeBivash is a cybersecurity strategist with 15+ years in network and application security, incident response, and threat intelligence, advising organizations across APAC. [Last Updated: October 06, 2025]

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