What Is a Backdoor Attack, and How Can You Prevent It?

What is a backdoor attack and why is it dangerous?

A backdoor attack is any type of attack that involves circumventing authentication protections to gain unauthorized access to a system.

For example, imagine you have an application that is designed to allow users to log in only if they enter a valid username and password. However, a threat actor who has compromised the server that hosts the application plants malware on the server to create a backdoor that allows unauthorized users to connect to the app using a special URL. This effectively sidesteps the normal authentication processes and enables unauthorized access to the app.

History of backdoor attacks

Since authentication and authorization controls were first introduced to computer systems a half-century ago, threat actors have been looking for ways to bypass them through backdoor attacks. Indeed, one of the earliest academic papers describing backdoor attacks dates to the late 1960s.

However, the challenge of protecting against backdoor attacks has grown worse over time due to the increased complexity of software systems. The use of multiple identity and access management (IAM) frameworks makes it harder in some cases to identify backdoor attack risks because each IAM solution may be subject to different vulnerabilities. Likewise, features like single sign-on (SSO), which allow users to authenticate once and connect to multiple applications, can exacerbate the impact of backdoor attacks in the event that breaching an SSO service gives threat actors access to multiple applications connected to that service.

How does a backdoor attack work?

Most backdoor attacks work in one of the following ways:

• Attackers exploit a preexisting vulnerability within an application (such as a vulnerable open source library) that allows them to execute arbitrary code as a way of defeating or circumventing standard access controls.
• Attackers plant their own malicious software within an application or on a host server that allows them to sidestep normal authentication and authorization procedures. They can launch this type of attack if they compromise the development environment used to build an application or the server that hosts it.
• Attackers identify a flaw within an application’s design – such as discovering that sensitive resources are available at a specific URL without logging in – that gives them access they were not intended to have. In this case, attackers don’t actually break in; they simply take advantage of an access path that developers did not expect them to know about.

Thus, there are many potential reasons why a backdoor attack could happen, and multiple steps that businesses must take to protect against backdoor attacks.

Types of backdoor attacks (with examples)

Backdoor attacks can be categorized based on the type of system they affect. Here’s a look at common types of backdoor attacks.

Application backdoor attacks

A backdoor attack against a specific application typically focuses on exploiting a flaw within the application itself.

For instance, application developers may have incorporated open source components into their application – such as the xz-utils, a set of open source data compression tools that were recently discovered to contain a backdoor vulnerability. If developers remain unaware of the vulnerability due to lack of visibility into their software supply chain, they may fail to take steps to address it, leaving their app vulnerable to attack.

In this case, the application backdoor attack would stem not from a flaw within original source code written by the application developers themselves, but instead from their use of a vulnerable third-party component.

Cloud backdoor attacks

In a cloud computing environment, threat actors often launch backdoor attacks by taking advantage of mistakes or oversights within cloud service configurations.

For example, they may discover that IAM rules grant anonymous users access to sensitive data housed in an object storage bucket. If they know the URLs where the data is hosted, they can view it without having to log in. Or, they may discover a cloud server that was launched based on a public image that included a default root username and password. If admins forget to change the credentials from the defaults, attackers would be able to log into the cloud server using publicly available login information.

Backdoor attacks on deep learning systems

Deep learning systems (such as generative AI models) that train on large data sets may be susceptible to backdoor attacks caused by manipulation of their training data. For instance, if threat actors devise a way to mislabel training data or inject malicious data into a training data set, the manipulated information may cause the model to behave in ways its developers did not intend.

This is a highly sophisticated type of backdoor attack that is more complex to execute than simply exploiting a security vulnerability. However, as deep learning models become more prevalent, this method of attack is likely to become more common, too.

Preventing a backdoor attack

Because there are many types of backdoor attacks and many techniques through which threat actors can potentially execute them, there is no simple way to guarantee that all of the software services your organization uses are safe from backdoor threats.

Instead, preventing backdoor attacks is a multi-step process that requires teams to implement protections at several stages of the software development lifecycle. Here’s a look at what this entails.

#1. Follow secure development practices

When developers write code, they should adhere to best practices such as:

• Avoiding the practice of hard-coding credentials into application source code or configuration code. If attackers gain access to hard-coded credentials, they could use them to sidestep normal authentication procedures.
• Making sure to obtain third-party software only from trusted sources.
• Implementing multi-factor authentication where appropriate to enhance the reliability of access control systems.

#2. Scan software for backdoor risks

No matter how much confidence you have in the security of your development practices, you should also scan software to identify risks that you may have overlooked during development.

You can do this using a tool like Trivy, an open source SBOM generation and security scanning solution. Trivy allows you to identify which components exist within your application, and then determine whether any of them are known to be insecure.

Taking matters further, you can deploy a Cloud Workload Protection Platform (CWPP) to help detect and prevent backdoor attacks in production. CWPPs offer an extra layer of protection against backdoor risks that you may have missed during pre-deployment scans.

#3. Deploy a CNAPP for comprehensive protection

In addition to adhering to secure application development standards and scanning software to identify risks, teams should deploy a Cloud Native Application Protection Platform (CNAPP), such as Aqua, to gain code to cloud protection.

A CNAPP helps secure applications at all stages of development and across all layers of your stack. This means that no matter where a backdoor exists – in your applications, your cloud environment, your deep learning models, or anywhere else – you can maximize your ability to detect and remediate the issue before threat actors exploit it.

Getting ahead of backdoor attacks

Backdoor attacks have been around for decades, and they’re not going to disappear anytime soon. The good news is that with the right practices and tools on your side, identifying backdoor security risks is quite feasible. It’s also critical, given the complexity of modern authentication and authorization processes and the serious repercussions that can result if threat actors successfully bypass standard access controls.