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 CODE RED • CVSS 9.9 • SUPPLY CHAIN ATTACK

   

WARNING: QNAP NAS Backup Flaw (CVE-2025-55315) Can Steal Your Credentials - Patch NOW!    

   

By CyberDudeBivash • October 28, 2025 •

 

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Disclosure: This is a security advisory for IT and security professionals. It contains affiliate links to relevant enterprise security solutions. Your support helps fund our independent research.

  Definitive Guide: Table of Contents  

1. Part 1: The Executive Briefing — A CVSS 9.9 Crisis in Your Backup Software
2. Part 2: Technical Deep Dive — A Masterclass on HTTP Request Smuggling
3. Part 3: The Defender's Playbook — An Urgent Guide to Patching and Mitigation
4. Part 4: The Strategic Takeaway — The Hidden Dangers of Software Dependencies
 

 

Part 1: The Executive Briefing — A CVSS 9.9 Crisis in Your Backup Software

 

QNAP has issued an urgent warning for a critical vulnerability affecting its **NetBak PC Agent**. This is not a simple bug; it is a **CVSS 9.9 (Critical)** vulnerability in a core Microsoft component that the QNAP software installs and depends on. The flaw, **CVE-2025-55315**, is a severe HTTP Request Smuggling vulnerability in the ASP.NET Core Kestrel web server.

For CISOs, this is a five-alarm fire. Your backup software—a tool you trust—has created a critical, internet-facing vulnerability on your Windows endpoints. An authenticated attacker can exploit this flaw to bypass security controls, hijack user credentials, access sensitive data, and even modify files on the server. This is a catastrophic failure of the software supply chain, and it requires immediate action.

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Part 2: Technical Deep Dive — A Masterclass on HTTP Request Smuggling (CVE-2025-55315)

What is HTTP Request Smuggling?

As we've detailed in our **Header Smuggling Masterclass**, this attack exploits inconsistencies in how different systems in a chain (like a front-end proxy and a back-end web server) parse an HTTP request. This specific flaw in the ASP.NET Kestrel server allows an attacker to "smuggle" a second, malicious HTTP request inside a seemingly benign one.

The Kill Chain

1. An attacker with low-level authentication sends a specially crafted HTTP request to the NetBak PC Agent's web server.
2. The front-end (if one exists) sees one request, but the vulnerable Kestrel backend sees two.
3. This "smuggled" second request is then processed by the application as if it came from a legitimate, trusted source.
4. This bypasses security checks, allowing the attacker to perform actions as another user, potentially leading to privilege escalation, session hijacking, and credential theft.

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Part 3: The Defender's Playbook — An Urgent Guide to Patching and Mitigation

QNAP and Microsoft have provided clear, non-negotiable remediation steps. You must act immediately.

1. PATCH IMMEDIATELY

You must update the vulnerable ASP.NET Core components on every single Windows machine running the NetBak PC Agent. QNAP recommends two methods:

• **Method 1 (Reinstall):** Uninstall your current NetBak PC Agent. Download the latest version from the QNAP website and install it. The new installer will automatically bundle the patched ASP.NET Core runtime.
• **Method 2 (Manual Update):** Manually go to the Microsoft .NET 8.0 download page and install the latest **ASP.NET Core Runtime (Hosting Bundle)**.

2. Hunt for Compromise (Assume Breach)

You must hunt for signs that this flaw was exploited. Your SOC team must immediately begin analyzing web server logs for any anomalous or malformed HTTP requests. A modern EDR/XDR is essential for detecting the post-exploitation behavior that would follow a successful credential hijack.

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Part 4: The Strategic Takeaway — The Hidden Dangers of Software Dependencies

 

For CISOs, this is a brutal and perfect case study in the systemic risk of the **software supply chain**. Your organization's security is not just dependent on the code your vendors write; it is dependent on *every single component and library* that their code depends on. A single flaw in a foundational, open-source component like ASP.NET Core can instantly create a critical vulnerability in dozens of trusted, "secure" enterprise applications in your environment.

This highlights the non-negotiable mandate for a mature **DevSecOps** and **Vulnerability Management** program that includes:

• **A Software Bill of Materials (SBOM):** You must demand an SBOM from your vendors so you know what components are running in your environment.
• **A Rapid, Enterprise-Wide Patching Capability:** When a flaw like this is announced, you must have the ability to patch not just the application, but its core dependencies, in a matter of hours.

 

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About the Author

   

CyberDudeBivash is a cybersecurity strategist with 15+ years in application security, DevSecOps, and supply chain risk management, advising CISOs across APAC. [Last Updated: October 28, 2025]

 

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