Dynamic application security testing

A dynamic application security testing (DAST) tool is a program which communicates with a web application through the web front-end in order to identify potential security vulnerabilities in the web application and architectural weaknesses. It performs a black-box test. Unlike static application security testing tools, DAST tools do not have access to the source code and therefore detect vulnerabilities by actually performing attacks. DAST tools allow sophisticated scans, detecting vulnerabilities with minimal user interactions once configured with host name, crawling parameters and authentication credentials. These tools will attempt to detect vulnerabilities in query strings, headers, fragments, verbs (GET/POST/PUT) and DOM injection.

Customers benefit from the convenience of these applications, while tacitly taking on risk that private information stored in web applications will be compromised through hacker attacks and insider leaks. According to the Privacy Rights Clearinghouse, more than 18 million customer records have been compromised in 2012 due to insufficient security controls on corporate data and web applications.

Overview

DAST tools facilitate the automated review of a web application with the expressed purpose of discovering security vulnerabilities and are required to comply with various regulatory requirements. Web application scanners can look for a wide variety of vulnerabilities, such as input/output validation: (e.g. cross-site scripting and SQL injection), specific application problems and server configuration mistakes.

In a copyrighted report published in March 2012 by security vendor Cenzic, the most common application vulnerabilities in recently tested applications include:

37%	Cross-site scripting
16%	SQL injection
5%	Path disclosure
5%	Denial-of-service
4%	Code execution
4%	Memory corruption
4%	Cross-site request forgery
3%	Information disclosure
3%	Arbitrary file
2%	Local file inclusion
1%	Remote file inclusion
1%	Buffer overflow
15%	Other (PHP injection, Javascript injection, etc.)

Commercial and open-source scanners

Commercial scanners are a category of web-assessment tools which need to be bought with a specific price (usually quite high). Some scanners include some free features but most need to be bought for full access to the tool's power.

And open-source scanners are another class which are free in nature. They are the best of the category since their source code is open and the user gets to know what is happening unlike commercial scanners.

Security researcher Shay Chen has previously compiled an exhaustive list of both commercial and open-source web application security scanners. The list also highlights how each of the scanners performed during his benchmarking tests against the WAVSEP.

The WAVSEP platform is publicly available and can be used to evaluate the various aspects of web application scanners: technology support, performance, accuracy, coverage and result consistency.

DAST strengths

These tools can detect vulnerabilities of the finalized release candidate versions prior to shipping. Scanners simulate a malicious user by attacking and probing, identifying results which are not part of the expected result set, allowing for a realistic attack simulation. The big advantage of these types of tools are that they can scan year-round to be constantly searching for vulnerabilities. With new vulnerabilities being discovered regularly this allows companies to find and patch vulnerabilities before they can become exploited.

As a dynamic testing tool, web scanners are not language-dependent. A web application scanner is able to scan engine-driven web applications. Attackers use the same tools, so if the tools can find a vulnerability, so can attackers.

DAST weaknesses

While scanning with a DAST tool, data may be overwritten or malicious payloads injected into the subject site. Sites should be scanned in a production-like but non-production environment to ensure accurate results while protecting the data in the production environment.

Because the tool is implementing a dynamic testing method, it cannot cover 100% of the source code of the application and then, the application itself. The penetration tester should look at the coverage of the web application or of its attack surface to know if the tool was configured correctly or was able to understand the web application.

The tool cannot implement all variants of attacks for a given vulnerability. So the tools generally have a predefined list of attacks and do not generate the attack payloads depending on the tested web application. Some tools are also quite limited in their understanding of the behavior of applications with dynamic content such as JavaScript and Flash.

A report from 2012 found that the top application technologies overlooked by most Web application scanners includes JSON (such as jQuery), REST, and Google WebToolkit in AJAX applications, Flash Remoting (AMF) and HTML5, as well as mobile apps and Web Services using JSON and REST. XML-RPC and SOAP technologies used in Web services, and complex workflows such as shopping cart, and XSRF/CSRF tokens.

External links

• Web Application Security Scanner Evaluation Criteria from the Web Application Security Consortium (WASC)
• Web Application Vulnerability Scanners, a wiki operated by the NIST
• Challenges faced by automated web application security assessment from Robert Auger
• The WASC security scanner list