Security Testing Basics
Software security testing is the process of assessing and testing a system to discover security risks
and vulnerabilities of the system and its data. There is no universal terminology but for our purposes,
we define assessments as the analysis and discovery of vulnerabilities without attempting to actually
exploit those vulnerabilities. We define testing as the discovery and attempted exploitation of
vulnerabilities.
Security testing is often broken out, somewhat arbitrarily, according to either the type of
vulnerability being tested or the type of testing being done. A common breakout is:
• Vulnerability Assessment – The system is scanned and analyzed for security
issues.
• Penetration Testing – The system undergoes analysis and attack from simulated
malicious attackers.
• Runtime Testing – The system undergoes analysis and security testing from an enduser.
• Code Review – The system code undergoes a detailed review and analysis looking
specifically for security vulnerabilities.
Note that risk assessment, which is commonly listed as part of security testing, is not
included in this list. That is because a risk assessment is not actually a test but rather the
analysis of the perceived severity of different risks (software security, personnel security,
hardware security, etc.) and any mitigation steps for those risks.
More About Penetration Testing
Penetration Testing (pentesting) is carried out as if the tester was a malicious external
attacker with a goal of breaking into the system and either stealing data or carrying out
some sort of denial-of-service attack.
Pentesting has the advantage of being more accurate because it has fewer false positives
(results that report a vulnerability that isn’t actually present), but can be time-consuming to
run.
Pentesting is also used to test defence mechanisms, verify response plans, and confirm
security policy adherence.
Automated pentesting is an important part of continuous integration validation. It helps to
uncover new vulnerabilities as well as regressions for previous vulnerabilities in an
environment which quickly changes, and for which the development may be highly
collaborative and distributed.
The Pentesting Process
Both manual and automated pentesting are used, often in conjunction, to test everything
from servers, to networks, to devices, to endpoints. This document focuses on web
application or web site pentesting.
Pentesting usually follows these stages:
• Explore – The tester attempts to learn about the system being tested. This includes
trying to determine what software is in use, what endpoints exist, what patches are
installed, etc. It also includes searching the site for hidden content, known
vulnerabilities, and other indications of weakness.
• Attack – The tester attempts to exploit the known or suspected vulnerabilities to
prove they exist.
• Report – The tester reports back the results of their testing, including the
vulnerabilities, how they exploited them and how difficult the exploits were, and the
severity of the exploitation.
Pentesting Goals
The ultimate goal of pentesting is to search for vulnerabilities so that these vulnerabilities
can be addressed. It can also verify that a system is not vulnerable to a known class or
specific defect; or, in the case of vulnerabilities that have been reported as fixed, verify that
the system is no longer vulnerable to that defect.
Introducing ZAP
Zed Attack Proxy (ZAP) is a free, open-source penetration testing tool being maintained
under the umbrella of the Open Web Application Security Project (OWASP). ZAP is designed
specifically for testing web applications and is both flexible and extensible.
At its core, ZAP is what is known as an “intercepting proxy.” It stands between the tester’s
browser and the web application so that it can intercept and inspect messages sent between
browser and web application, modify the contents if needed, and then forward those packets
on to the destination. In essence, ZAP can be used as a “man in the middle,” but also can be
used as a stand-alone application, and as a daemon process.
If there is another network proxy already in use, as in many corporate environments, ZAP
can be configured to connect to that proxy.
ZAP provides functionality for a range of skill levels – from developers, to testers new to
security testing, to security testing specialists. ZAP has versions for each major OS and
Docker, so you are not tied to a single OS. Additional functionality is freely available from a
variety of add-ons in the ZAP Marketplace, accessible from within the ZAP client.
Because ZAP is open-source, the source code can be examined to see exactly how the
functionality is implemented. Anyone can volunteer to work on ZAP, fix bugs, add features,
create pull requests to pull fixes into the project, and author add-ons to support specialized
situations.
For more information, see the Zed Attack Proxy Project Page.
As with most open source projects, donations are welcome to help with costs for the
projects. You can find a donate button on the owasp.org page for ZAP at
https://www.owasp.org/index.php/ZAP.
Install and Configure ZAP
ZAP has installers for Windows, Linux, and Mac OS/X. There is also a Docker image available
on the download site listed below.
Install ZAP
The first thing to do is install ZAP on the system you intend to perform pentesting on.
Download the appropriate installer from ZAP’s download location at
https://github.com/zaproxy/zaproxy/wiki/Downloads and execute the installer.
Note that ZAP requires Java 7+ in order to run. The Mac OS/X installer includes an
appropriate version of Java but you must install Java 7+ separately for Windows, Linux, and
Cross-Platform versions. The Docker version does not require you to install Java.
Once the installation is complete, launch ZAP and read the license terms. Click Agree if you
accept the terms, and ZAP will finish installing, then the ZAP will automatically start.
Persisting a Session
When you first start ZAP, you will be asked if you want to persist the ZAP session. By default,
ZAP sessions are always recorded to disk in a HSQLDB database with a default name and
location. If you do not persist the session, those files are deleted when you exit ZAP.
If you choose to persist a session, the session information will be saved in the local database
so you can access it later, and you will be able to provide custom names and locations for
saving the files.
For now, select No, I do not want to persist this session at this moment in time, then
click Start. The ZAP sessions will not be persisted for now.
ZAP UI
The ZAP UI is composed of the following elements:
1. Menu Bar – Provides access to many of the automated and manual tools.
2. Toolbar – Includes buttons which provide easy access to most commonly used
features.
3. Tree Window – Displays the Sites tree and the Scripts tree.
4. Workspace Window – Displays requests, responses, and scripts and allows you to
edit them.
5. Information Window – Displays details of the automated and manual tools.
6. Footer – Displays a summary of the alerts found and the status of the main
automated tools.
While using ZAP, you can click Help on the Menu Bar or press F1 to access context-sensitive
help from the ZAP User Guide.
For more information about the UI, see ZAP UI Overview in the ZAP online documentation.
ZAP also supports a powerful API and command line functionality, both of which are beyond
the scope of this guide.
Configure Your Browser to Proxy Through ZAP
Before you can begin to run pentests with ZAP, you have to configure your browser to use
ZAP as its proxy. By default, ZAP uses:
Address: localhost
Port: 8080
If you don’t know how to change your browser’s proxy, see Configuring Proxies in the ZAP
online documentation or refer to the help for your browser.
Import and Trust the ZAP Root CA Certificate
Since ZAP is set up to act as a proxy between your browser and the web application, using
SSL (HTTPS) will cause the certificate validation to fail and the connection to be terminated.
This is because ZAP encrypts and decrypts traffic sent to the web application using the
original web application certificate. This is done so that ZAP can access the plain text in the
requests and responses.
To prevent this failure from happening, ZAP automatically creates an SSL certificate for each
host you access, signed by ZAP’s own Certificate Authority (CA) certificate. To have your
browser trust these SSL certificates, you need to first import and trust the ZAP Root CA
certificate. Once it is trusted, the other ZAP SSL certificates signed by it will be trusted as
well.
It’s important to note that, although the self-generated Root CA certificate is uniquely
generated for you, it still must be kept private to avoid creating a vulnerability.
To export the ZAP Root CA certificate:
1. Start ZAP and click Tools -> Options.
2. On the left pane of the Options window, click Dynamic SSL Certificates.
3. On the right pane, click Save.
4. Select a location to save the certificate to and click Save. Be sure to retain the .cer
file extension.
To install the ZAP Root CA certificate as a trusted root certificate for Windows / Internet
Explorer:
1. Navigate to the certificate file.
2. Right-click on the certificate file and then click Install Certificate.
3. In the Certificate Import Wizard, select either Current User or Local Machine as
the scope of the certificate, then click Next.
4. Select Place all certificates in the following store.
5. Click Browse and select Trusted Root Certificate Authorities or Trusted Root
Certificates (depending on your version of Windows) as the certificate store, then
click Next.
6. Click Finish.
7. Review the security warning about trusted root certificates and click Yes if the
warning is accepted.
To verify that the ZAP Root CA certificate is installed:
1. Open Control Panel and click Internet Options.
2. On the Content tab, in the Certificates section, click Certificates.
3. On the Trusted Root Certificates tab, verify that the OWASP ZAP Root CA
certificate is listed.
If you are testing using Firefox, you need to install the ZAP Root CA certificate a second time
into Firefox’s own certificate store.
To install the ZAP Root CA for Mozilla Firefox:
1. Start Firefox and click Preferences.
2. On the Advanced tab, click the Encryption tab.
3. Click View Certificates.
4. On the Trusted root certificates tab, click Import and select the ZAP Root CA file
you saved previously.
5. In the Import wizard, select Trust this CA to identify web sites.
6. Click OK.
For more information about ZAP and SSL certificates, see Option Dynamic SSL Certificates.
For more information about trusted root certificates and browsers or operating systems not
listed above, see the help files for your specific browser or operating system.
Try to Connect Your Web Application
Once you have configured your browser to use ZAP as its proxy, open your browser and
attempt to connect to the web application you are going to test.
If you are unable to reach your web application, check the following:
1. Verify the proxy settings the browser is using to connect to ZAP.
2. Verify the proxy settings in ZAP are those the browser is using to try to connect to
ZAP.
3. Verify the web application you want to test is running.
4. Check to see whether your network requires a proxy to reach your web application. If
so, you may need to configure ZAP to use a proxy.
To configure ZAP to use an outgoing proxy:
1. Start ZAP and on the Menu Bar, click Tools -> Options.
2. Select Connection in the left pane.
3. In the use proxy chain section of the Connection settings, check the Use an
outgoing proxy server checkbox.
4. Enter the Address/Domain Name and Port for your network proxy.
5. Click OK to save the settings and verify that you can now connect to your web
application.
Once your browser can successfully connect to your web application, you are ready to run a
test.
Start Pentesting with ZAP
The easiest way to start using ZAP is to run a Quick Start test. Quick Start is a ZAP add-on
that was installed automatically when you installed ZAP.
IMPORTANT: You should only use ZAP to attack an application you have permission to test
with an active attack. Because this is a simulation that acts like a real attack, actual damage
can be done to a site’s functionality, data, etc. If you are worried about using ZAP, you can
prevent it from causing harm (though ZAP’s functionality will be significantly reduced) by
switching to safe mode.
To switch ZAP to safe mode, click the arrow on the mode dropdown on the main toolbar to
expand the dropdown list and select Safe Mode.
Run a Quick Start Test
To run a Quick Start test:
1. Start ZAP and click the Quick Start tab of the Workspace Window.
2. In the URL to attack text box, enter the full URL of the web application you want to
attack.
3. Click the Attack button.
ZAP will proceed to crawl the web application with its spider, then passively scan each page
it finds. Then ZAP will use the active scanner to attack all of the discovered pages,
functionality, and parameters.
Interpret Your Test Results
As ZAP spiders your web application, it constructs a map of your web applications’ pages
and the resources used to render those pages. Then it records the requests and responses
sent to each page and creates alerts if there is something potentially wrong with a request
or response.
See Explored Pages
To examine a tree view of the explored pages, click the Sites tab in the Tree Window. You
can expand the nodes to see the individual URLs accessed.
View Alerts and Alert Details
The left-hand side of the Footer contains a count of the Alerts found during your test, broken
out into risk categories. These risk categories are:
To view the alerts created during your test:
1. Click the Alerts tab in the Information Window.
2. Click each alert displayed in that window to display the URL and the vulnerability
detected in the right side of the Information Window.
3. In the Workspace Windows, click the Response tab to see the contents of the header
and body of the response. The part of the response that generated the alert will be
highlighted.
Expand Your Pentesting with ZAP
The passive scanning and automated attack functionality is a great way to begin a
vulnerability assessment of your web application but it has some limitations. Among these
are:
• Any pages protected by a login page are not discoverable during a passive scan
because, unless you’ve configured ZAP’s authentication functionality, ZAP will not
handle the required authentication.
• Any pages that are not findable with ZAP’s default spider are not testable during a
passive scan. ZAP does provide additional options for discovery and coverage outside
of passive scanning.
• You don’t have a lot of control over the sequence of exploration in a passive scan or
the types of attacks carried out in an automated attack. ZAP does provide many
additional options for exploration and attacks outside of passive scanning.
Configure and Run a Spider with ZAP
One way to expand and improve your testing is to change the spider ZAP is using to explore
your web application. Quick Scan uses the traditional ZAP spider, which discovers links by
examining the HTML in responses from the web application. This spider is fast, but it is not
always effective when exploring an AJAX web application that generates links using
JavaScript.
For AJAX applications, ZAP’s AJAX spider is likely to be more effective. This spider explores
the web application by invoking browsers which then follow the links that have been
generated. The AJAX spider is slower than the traditional spider and requires additional
configuration for use in a “headless” environment.
A simple way to switch back and forth between spiders is to enable a tab for each spider in
the Information Window and use that tab to launch scans.
1. In the Information Window, click the green plus sign (+).
2. Click Spider to create a Spider tab.
3. Repeat step 1, then click AJAX Spider to create an AJAX Spider tab.
4. Click the push-pin symbol on both the Spider and AJAX Spider tabs to pin them to
the Information Window.
Note that both of these tabs include a New Scan button.
Explore Your Site
Spiders are a great way to explore your basic site, but they should be combined with manual
exploration to be more effective. Spiders, for example, will only enter basic default data into
forms in your web application but a user can enter more relevant information which can, in
turn, expose more of the web application to ZAP. This is especially true with things like
registration forms where a valid email address is required. The spider may enter a random
string, which will cause an error. A user will be able to react to that error and supply a
correctly formatted string, which may cause more of the application to be exposed when the
form is submitted and accepted.
Since you have configured your browser to use ZAP as its proxy, you should explore all of
your web application with that browser. As you do this, ZAP passively scans all the requests
and responses made during your exploration for vulnerabilities, continues to build the site
tree, and records alerts for potential vulnerabilities found during the exploration.
It is important to have ZAP explore each page of your web application, whether linked to
another page or not, for vulnerabilities. Obscurity is not security, and hidden pages
sometimes go live without warning or notice. So be as thorough as you can when exploring
your site.
Run an Active Scan with ZAP
So far ZAP has only carried out passive scans of your web application. Passive scanning does
not change responses in any way and is considered safe. Scanning is also performed in a
background thread to not slow down exploration. Passive scanning is good at finding some
vulnerabilities and as a way to get a feel for the basic security state of a web application and
locate where more investigation may be warranted.
Active scanning, however, attempts to find other vulnerabilities by using known attacks
against the selected targets. Active scanning is a real attack on those targets and can put
the targets at risk, so do not use active scanning against targets you do not have permission
to test.
To start an active scan:
1. In the Tree View, in the Sites tab, select the sites you want to perform an active scan
on.
2. Right-click the selected sites and select Active Scan.
or
1. In the Information Window, select the Active Scan tab.
2. Click New Scan.
To review and modify your settings, then begin an active scan:
1. In the Menu Bar, click Tools -> Active Scan.
2. Review the settings and make any changes you wish to.
3. Click Start Scan to start the Active Scan with these settings.
You can review the results of your active scan the same way you reviewed the results of your
passive scan, as shown in Interpret Your Test Results.
Learn More About ZAP
Now that you are familiar with a few basic capabilities of ZAP, you can learn more about
ZAP’s capabilities and how to use them from ZAP’s User Guide. The User Guide provides
step-by-step instructions, references for the API and command-line programming,
instructional videos, and tips and tricks for using ZAP.
Useful Links
OWASP Zed Attack Proxy Project – ZAP’s main project page
OWASP ZAP Wiki – The ZAP Wiki
OWASP ZAP User Guide - The ZAP User Guide
OWASP ZAP Hot Keys - The list of ZAP hotkeys
ZAP Proxy Users Group – Google group for ZAP users
ZAP Proxy Developers Group – Google group for developers and contributors to ZAP