Nuclei: What an OpenSource Vulnerability Scanner Can Do

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Vulnerability scanners are used everywhere in information security. One of the most common is Nuclei, an open-source scanner. In this article, we will consider its characteristics, usage scenarios, and similar solutions.

Key Features of Nuclei​

Nuclei is a fast, customizable vulnerability scanner designed to scan applications, infrastructure, cloud platforms, and networks to identify and remediate CVEs that attackers can exploit. Allows you to develop custom vulnerability detection scenarios that simulate real-world conditions.

At its core, Nuclei uses templates, represented as simple YAML files, that describe methods for detecting, ranking, and remediating specific security flaws. Each template describes a possible attack path: a vulnerability, its severity, a priority rating, and sometimes associated exploits. This methodology ensures that Nuclei not only identifies potential threats, but also identifies exploitable vulnerabilities with tangible, real-world consequences.

Sergey Polunin.
Head of the Infrastructure IT Solutions Protection Group at Gazinformservice.

The main Nuclei template is an HTTP template used to test web applications. This is not surprising, because web applications make up the vast majority of all products being developed and their testing is in high demand. Accordingly, this template allows you to search for SQL injections, XSS, configuration errors and similar vulnerabilities.

In addition, there are TCP and UDP templates, which allows Nuclei to work as a classic application vulnerability scanner. However, testing scenarios can be different and templates are provided for this, for example, for DNS servers, searching for specific files or testing SSL/TLS configurations. All templates are written in a convenient YAML format and allow for very flexible configuration. Thus, you can select an existing template for your testing scenario or quickly develop your own.

In addition to the simple YAML format for creating and flexibly customizing vulnerability templates, as well as open source code, the following key features of Nuclei can be highlighted:

1. Universal target specification: Supports various target specification parameters such as URLs, IP ranges, ASN ranges, and input files, providing flexibility in defining the scan scope.
2. Mass scanning. Ability to efficiently scan multiple targets at once.
3. Simulates real vulnerability testing actions, reducing the number of false positives.
4. Ultra-fast parallel scan processing and query clustering.
5. Integration into CI/CD pipelines for vulnerability detection and regression testing.
6. Support for protocols such as TCP, DNS, HTTP, SSL, WHOIS JavaScript, Code and others.
7. Integration with Jira, Splunk, GitHub, Elastic, GitLab.

Nuclei offers a vast collection of templates covering various types of vulnerabilities and attacks. With over 6,500 templates contributed so far, the scanner is constantly updated with real exploits and advanced attack vectors. Nuclei also makes it easy to add new tests and customize your scans. This makes it popular with researchers and bug hunters who test specific vulnerabilities.

How to use Nuclei​

To install Nuclei, you can download the executable file from the official GitHub repository and run the installation command. After that, you need to select templates from the Nuclei library, which covers various types of vulnerabilities such as SQL injection, XSS, and others. Nuclei templates support scanning for critical issues such as Log4j and RCE vulnerabilities that affect vendors such as GitLab, Cisco, F5, and many others. You can also create your own templates by specifying scanning parameters as per your needs.

Nikita Raspopov.
Security Analysis Specialist at the UCSB.

The list of the main types of Nuclei templates is as follows: Network, DNS, HTTP, FIle, Websockets, Headless, Javascript, Flow, Code, Multiprotocol. As you can see from this list, Nuclei allows you to implement almost any check.

For example, at the network protocol level, we can list available ports or check for the possibility of DNS-related attacks, such as DNS rebinding. At the web application level, you can implement a check for the presence of default credentials or for access to potentially sensitive files and directories, such as .git. Given the level of Nuclei's flexibility, the main thing is to correctly formulate the task for yourself, and then you can create the necessary template or use a ready-made one.

Once the templates are selected, you can start scanning. Nuclei supports parallel scanning, which significantly speeds up the scanning process. To start scanning, specify the targets and the selected templates. Nuclei can scan both single targets and target lists. Once the scan is complete, the tool provides detailed reports on the vulnerabilities found, which can be exported to various formats for further analysis and remediation.

How and for whom is Nuclei useful?​

Nuclei has dozens of use cases across various areas of information security, including:

1. Web Application Security: Scanner identifies common web vulnerabilities using community-developed patterns.
2. Infrastructure Security: Checks server configurations, open ports, and insecure services for security issues.
3. API Security Testing: Tests APIs for known vulnerabilities and misconfigurations.
4. Security (CI/CD): Integrates into CI/CD pipelines to minimize the re-introduction of vulnerabilities into production.
5. Third-party vendor assessment. Scans the vendor's digital assets.
6. Cloud Security: Scans cloud environments for misconfigurations and vulnerabilities.
7. Mobile App Security: Scans mobile apps for security issues, including API tests and configuration checks.
8. Network Device Security: Identifies vulnerabilities in network devices such as routers, switches, and firewalls.
9. Web Server Assessment: Identifies common vulnerabilities and misconfigurations in web servers.
10. Content Management System Assessment. Identifies vulnerabilities specific to CMS platforms such as WordPress, Joomla or Drupal.
11. Database Security Assessment: Scans databases for known vulnerabilities, default configurations, and access control issues.

Such wide application possibilities of Nuclei make it a popular tool among various information security specialists. For example, it can be used in their work by:

• security engineers and analysts to assess security and identify vulnerabilities;
• red teams to simulate real attack scenarios and identify weaknesses;
• DevOps teams integrate Nuclei into their CI/CD pipelines to ensure continuous security and mitigate user vulnerabilities;
• bug hunters to find vulnerabilities in bug bounty programs;
• pentesters to automate their assessment methods.

Nuclei is useful for various scenarios such as web security, infrastructure auditing, API testing, and cloud platform security assessment, making it an indispensable tool for security professionals, developers, and DevOps teams.

Similar solutions​

Among the solutions similar to Nuclei, we can highlight several of the most popular ones, such as Nessus, OpenVAS, Burp Suite, Qualys, Nikto.

Nessus is a popular vulnerability scanner developed by Tenable. It provides the ability to automatically scan networks and systems for vulnerabilities such as SQL injection, XSS, and more. Nessus supports multiple platforms and can be integrated with vulnerability management systems.

OpenVAS is a free version of a vulnerability scanner based on the Nessus project. It provides a wide range of tests to detect vulnerabilities in various systems and networks. OpenVAS supports many platforms and can be configured for various scanning scenarios.

Burp Suite is a comprehensive web application security testing tool. It includes a proxy server, vulnerability scanner, vulnerability analysis and exploitation tools. Burp Suite is widely used in the industry for web application security testing.

Qualys is a vulnerability management and security platform. It provides the ability to scan networks, web applications, and cloud platforms for vulnerabilities. Qualys also offers real-time vulnerability monitoring and management.

Nikto is a free web server scanner designed to find vulnerabilities and weaknesses in web applications. It checks for known vulnerabilities such as outdated software versions and weak passwords. Nikto supports many web servers and can be easily integrated into scanning systems.

Nikita Raspopov.
Security Analysis Specialist at the UCSB.

Nuclei is unique due to its wide customization capabilities and ease of use. You can download the utility as a standalone file from GitHub and immediately use it in your projects, unlike the heavyweight Nessus and OpenVAS, which require a full installation. In addition, Nuclei is an open source project, which makes it available to everyone, unlike the same Nessus.

OpenVAS has a free version, but its functionality is severely limited. It is also worth noting that Nuclei is easily integrated into your own automation tools, which saves time and, combined with the ability to write your own templates, allows you to conduct spot checks with the conditions necessary for the task. Moreover, Nuclei is easily integrated into CI/CD pipelines.

These tools provide various approaches and capabilities for ensuring the security of information systems, helping organizations identify and eliminate vulnerabilities in their infrastructures. Among them, Nuclei stands out for its flexibility, high speed of operation and the possibility of deep customization.

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