What is a backdoor attack?

The results of a backdoor attack can be severe. Infiltrators can move laterally throughout the network, escalate privileges, and carry out data theft attacks. They may also remain resident for long periods, creating a persistent data breach risk.

How does a backdoor attack work?

Closing exposed backdoors is a critical network security challenge, and prevention begins with understanding how a backdoor attack works.

Backdoor attacks leverage existing network security vulnerabilities and use specialist malware to create clandestine access points.

Most attacks require an existing security vulnerability to enable initial access. For example, attackers may exploit unpatched software, insecure software configurations, or weak user credentials. Remote access tools are a common target, but attackers could also use browser plugins, IoT firmware, and compromised DevOps tools.

When attackers detect a vulnerability, they create a network backdoor. This could involve injecting malicious code, delivering malware via phishing emails, bundling Trojans with legitimate software, or supply chain compromises targeting third-party tools.

Imagine a secured vault with reinforced doors, security guards, laser sensors, and timed access. This vault appears secure. However, the various security systems mean nothing if thieves can gain access via nearby sewers or ventilation shafts.

These covert methods are like backdoor attacks, and companies need to plan their security systems carefully to protect their assets.

Types of backdoor attacks

There are several types of backdoor attacks, which further complicate the task for security teams. Common techniques include:

Maintenance hook attacks

These attacks exploit the "maintenance hooks" developers insert into applications to test code and fix bugs. These pass-throughs often work around authentication measures while providing extensive network privileges.

Developers also sometimes forget to remove maintenance hooks following installation, and skilled attackers can scan systems to determine whether this is the case.

Hidden channels

Applications and systems require protocols for routine data transfers. However, criminals can hijack transfer protocols and create covert channels within the network. Attackers can encode data in packet headers, DNS queries, or even images, allowing undetected data theft.

Disguising exfiltration as legitimate transfers makes this type of backdoor attack difficult to detect by standard Intrusion Detection Systems (IDS).

Application and kernel-level installation

Kernels manage the relationships between hardware and software components, but can also act as a vector for backdoor attacks. In these attacks, criminals implant malicious kernel rootkits and use them to gain network access.

Application-level attacks create backdoors in apps installed on the network. Backdoors may exploit existing application code or add malicious code to hijack software. Detecting this technique is challenging as the subsequent backdoor resembles normal application functioning.

Hardware backdoors

This backdoor attack type is different as it uses physical devices to infiltrate networks. Hackers gain access to servers or other network infrastructure and modify them to enable malicious access.

For instance, attackers could insert chips that change firmware to bypass access controls. Modification could happen before devices are delivered, whether vendors are aware, or not. However, attackers can also access hardware during maintenance tasks or breach physical security measures.

Understanding risks related to backdoor attacks

We all know that leaving your backdoor open to outsiders will eventually expose the contents of your home to thieves. The same applies to a network backdoor attack. However, the implications of unfixed backdoors go beyond data loss.

Backdoors are a critical security threat for several reasons:

• Backdoor attacks are persistent: Skilled attackers create backdoors undetected and keep that access point open for long periods. Persistence enables attackers to carry out long-term surveillance (a valuable tool for corporate espionage attacks).
• They lead to malware deployment: Attackers with persistent network access can research the network to detect valuable assets. They can use their privileges to spread malware needed to launch ransomware attacks, and target encryption against the most important data.
• Backdoors allow unauthorized access to confidential data: Malicious attackers use backdoors to enter and leave networks as they please. If networks lack internal security measures (such as network segmentation and data loss prevention tools), attackers roam freely and exfiltrate sensitive information.
• Attackers can damage network assets: Data theft is not the only harm attackers can inflict. Backdoors allow criminals to edit data, access confidential documents, change network settings, and disable applications. In worst-case scenarios, a backdoor attack results in system downtime and irreparable damage.
• They put supply chains at risk: Attackers target IT vendors and developers with many downstream clients. Adding backdoors to widely used tools amplifies the force of attacks and can devastate businesses with complex supply chains.
• Backdoors add compliance risk: Backdoors represent a critical privacy threat. Companies that fail to close backdoor threats may expose customer data to malicious attackers and incur significant compliance penalties. This also represents a reputational and financial risk.

Examples of backdoor attacks

Criminals continuously look for backdoors, and they often find them. There have been many real-world examples of back door attacks, with serious consequences for the organizations involved. Here are a few examples that show evolving intrusion and weaponization techniques.

1. Solar Winds

The 2020 Solar Winds attack affected over 18,000 clients in the IT management firm's supply chain.

In this attack, members of the Russian Cozy Bear collective implanted a backdoor attack known as Sunburst. Sunburst modified code in Solar Winds' Orion IT monitoring software, allowing threat actors to gain access to client networks.

Even worse, the Solar Winds attack took 9 months to detect, highlighting the persistence of backdoor attacks and their covert nature.

2. Microsoft Teams

A 2025 backdoor attack against Microsoft Teams shows how backdoors interact with vishing (video phishing) techniques.

In this emerging attack, criminals pose as legitimate maintenance experts, using Teams to place calls to potential victims. As the call progresses, attackers use DLL sideloading to execute a malicious script, which generates a Start Menu LNK file. After that, a Java command and control tool allows attackers to issue commands on the victim's device.

3. TookPS: using fake apps to spread malware

Another recent backdoor attack uses fake versions of trusted sites and apps. Known as TookPS, this backdoor agent has spread via compromised AutoCAD and SketchUp downloads, along with fake versions of the Deepseek front end.

When downloaded, these tools deliver TookPS malware, which uses PowerShell to retrieve command and control software from the attackers. TookPS also creates an authenticated SSH server to give attackers control over the victim's device.

This attack shows the close connection between web protection and backdoors. Companies must scan unsafe downloads for malware signatures and block fake websites to prevent backdoor attacks.

How to detect and prevent a backdoor attack

Backdoors should always remain closed, so how can you prevent backdoor attacks and secure critical network assets? Companies must take a comprehensive approach to the backdoor malware threat, and use cutting-edge tools to block emerging techniques.

Use the list of best practices below as a foundation for your strategy:

• Protect your attack surface: Endpoint protection tools scan for vulnerabilities and detect untrusted software on endpoints. Security teams can also minimize the attack surface by closing open ports and unnecessary services, using strict criteria to approve new app installations.
• Apply network segmentation: Network segmentation creates secure zones protected by Zero Trust verification. This helps prevent backdoor attacks by reducing the scope for lateral movement. Attackers cannot access sensitive resources without bypassing robust access controls. Simply gaining access is not sufficient.
• Create a systematic patch management system: Outdated software is far more vulnerable to backdoor exploits. Set your operating system to update all tools installed on the network and replace deprecated software as soon as possible. External scanning tools also check for unpatched assets. This assures security teams that every vulnerability is under control.
• Use download protection: NordLayer's download protection tools scan incoming downloads for known malware threats and quarantine suspicious files. They use threat intelligence to assess the reputation of download sites, giving users more knowledge about whether to install apps or accept plugins.
• Use Intrusion Detection Systems: IDS tools monitor endpoints to detect cyber threats entering the network and track user activity to detect activated backdoor malware.
• Protect connections with Virtual Private Networks (VPNs): VPNs can help prevent backdoor attacks by encrypting user connections. Attackers gaining access via backdoors cannot read encrypted traffic and find it harder to gain unauthorized access without VPN credentials. VPNs also cut the risk of man-in-the-middle attacks that enable the spread of backdoor malware.
• Train employees to understand backdoor risks: Training is increasingly important to counter backdoor attacks. For example, attackers use vishing to deliver sideloaded malware. Staff should know the need for caution when accepting video calls. They must understand the importance of verifying identities before establishing remote access connections.
• Be smart about supply chain security: Assess IT vendors based on their security record, and avoid suppliers with a history of security failures. Integrate third-party apps into your Zero Trust security architecture, and manage third-party privileges to limit access when not required.

Safeguard your network backdoor to secure critical assets

Backdoors allow unauthorized access to network assets, putting data and operational systems at risk. These covert threats are persistent, hard to detect, and evolving to harness advanced phishing techniques.

Companies can respond by implementing endpoint protection, operating system updates, download protection, and Zero Trust controls. Staff training, vendor risk assessments, and VPN tools also help manage backdoor risks and secure your data.