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Leveraging Dev Tools

This appendix outlines various details for use of in browser Developer Tool functionality to aid in security testing activities.

Obviously in browser functionality is not a substitute for: DAST (Dynamic Application Security Testing) tools, SAST (Static Application Security Testing) tools, or a tester’s experience, however, it can be leveraged for some testing activities and report production related tasks.

Accessing Dev Tools

Opening Dev Tools can be accomplished in a number of ways.

  1. Via the keyboard shortcut F12.
  2. Via the keyboard shortcut ctrl + shift + i on Windows.
  3. Via the keyboard short cut cmd + option + i on Mac.
  4. Via the web page right-click context menu and then selecting Inspect in Google Chrome.
  5. Via the web page right-click context menu and then selecting Inspect Element in Mozilla Firefox.
  6. Via the triple dot ‘kabob’ menu in Google Chrome then selecting More Tools and then Developer Tools.
  7. Via the triple line ‘hamburger’ (or ‘pancake’) menu in Mozilla Firefox then selecting Web Developer and then Toggle Tools.
  8. Via the gear icon settings menu in Edge/IE then selecting Developer Tools.

NOTE: The majority of the instructions below assume that Dev Tools is already open or active.

Capabilities

Functionality Chrome* Firefox Edge/IE Safari
User-Agent Switching Y Y Y Y
Edit/Resend Requests Y Y N N
Cookie Editing Y Y Y N
Local Storage Editing Y Y Y N
Disable CSS Y Y Y Y
Disable JavaScript Y Y N Y
View HTTP Headers Y Y Y Y
Screenshots Y Y Y N
Offline Mode Y Y N N
Encoding and Decoding Y Y Y Y
Responsive Design Mode Y Y Y Y

* Anything that applies to Google Chrome should be applicable to all Chromium based applications. (Which includes Microsoft rebadging Edge around 2019/2020.)

User-Agent Switching

Google Chrome

  1. Click on triple dot ‘kabob’ menu on the right side of the Developer Tools pane, select More tools then select Network conditions.
  2. Un-check the “Select automatically” checkbox.
  3. Select the user agent from dropdown menu or enter a custom user agent

User-Agent selection dropdown menu in Google Chrome
Figure 6.F-1: Google Chrome Dev Tools User-Agent Switching Functionality

Mozilla Firefox

  1. Navigate to Firefox’s about:config page and click I accept the risk!.
  2. Enter general.useragent.override into the search field.
  3. Look for general.useragent.override, if you can’t see this preference, look for one that show a set of radio buttons Boolean, Number, String select String then click the plus sign Add button on the about:config page.
  4. Set the value of general.useragent.override to whatever User-Agent you might need.

User-Agent configuration preference in Mozilla Firefox
Figure 6.F-2: Mozilla Firefox User-Agent Switching Functionality

Later click on the garbage can Delete button to the right of the general.useragent.override preference to remove the override and switch back to the default user agent.

Edit/Resend Requests

Mozilla Firefox

  1. Select the Network tab.
  2. Perform any action in the web application.
  3. Right-click on the HTTP request from the list and select Edit and Resend.
  4. Make desired modifications and click on the Send button.
  5. Right-click on the modified request and select Open in New Tab.

Google Chrome

  1. Select the Network tab.
  2. Perform any action in the web application.
  3. Right-click on the HTTP request from the list and select Copy > Copy as fetch.
  4. Paste the provided JavaScript code into the Console tab.
  5. Make any required modifications, and then hit enter to send the request.

Google Chrome

  1. Click the Application tab.
  2. Expand Cookies under the Storage heading.
  3. Select the relevant domain name.
  4. Double click in the Value column to edit any cookie value.

Note: Cookies can be deleted once selected by pressing the delete key, or from the right-click context menu.

Mozilla Firefox

  1. Click the Storage tab.
  2. Expand the Cookies section.
  3. Select the relevant domain name.
  4. Double click in the Value column to edit any cookie value.

Note: Cookies can be deleted once selected by pressing the delete key, or with various options from the right-click context menu.

Cookie Editing functionality in Mozilla Firefox
Figure 6.F-3: Mozilla Firefox Cookie Editing Functionality

Local Storage Editing

Google Chrome

  1. Click the Application tab.
  2. Expand Local Storage under the Storage heading.
  3. Select the relevant domain name.
  4. Double click in the Value column to edit any cookie value.
  5. Double click in the applicable Cell to edit the Key or Value.

Note: Editing Session Storage or Index DB follows essentially the same steps.

Note: Items can be added or deleted via the right-click context menu.

Mozilla Firefox

  1. Click the Storage tab.
  2. Expand the Local Storage section.
  3. Select the relevant domain name.
  4. Double click in the applicable Cell to edit the Key or Value.

Note: Editing Session Storage or Index DB follows essentially the same steps.

Note: Items can be added or deleted via the right-click context menu.

Disable CSS

General

All major browsers support manipulating CSS leveraging the Dev Tools Console and JavaScript functionality:

  • To remove all external style-sheets: $('style,link[rel="stylesheet"]').remove();
  • To remove all internal style-sheets: $('style').remove();
  • To remove all in-line styles: Array.prototype.forEach.call(document.querySelectorAll('*'),function(el){el.removeAttribute('style');});
  • To remove everything from head tag: $('head').remove();

Disable JavaScript

Google Chrome

  1. Click on triple dot ‘kabob’ menu on the right side of the web developer toolbar and click on Settings.
  2. On the Preferences tab, under the Debugger section, check the Disable JavaScript checkbox.

Mozilla Firefox

  1. On the dev tools Debugger tab, click on the settings gear button in the upper right corner of the developer toolbar.
  2. Select Disable JavaScript from the dropdown (this is an enable/disable menu item; when JavaScript is disabled, the menu item has a check mark).

View HTTP Headers

Google Chrome

  1. On the Networking tab in Dev Tools select any URL or request.
  2. In the lower right hand pane select the Headers tab.

Headers View in Google Chrome
Figure 6.F-4: Google Chrome Headers View

Mozilla Firefox

  1. On the Networking tab in Dev Tools select any URL or request.
  2. In the lower right hand pane select the Headers tab.

Headers View in Mozilla Firefox
Figure 6.F-5: Mozilla Firefox Headers View

Screenshots

Google Chrome

  1. Press on the Toggle Device Toolbar button or press ctrl + shift + m.
  2. Click the triple dot ‘kabob’ menu in the Device Toolbar.
  3. Select Capture screenshot or Capture full size screenshot.

Mozilla Firefox

  1. Press the triple dot ellipsis button in the address bar.
  2. Select Take a Screenshot.
  3. Select either the Save full page or Save visible option.

Offline Mode

Google Chrome

  1. Navigate to Network tab.
  2. In the Throttle dropdown select Offline.

Offline Option in Google Chrome
Figure 6.F-6: Google Chrome Offline Option

Mozilla Firefox

  1. From the triple line ‘hamburger’ (or ‘pancake’) menu select Web Developer and then Work Offline.

Offline Option in Mozilla Firefox
Figure 6.F-7: Mozilla Firefox Offline Option

Encoding and Decoding

General

All major browsers support encoding and decoding strings in various ways leveraging the Dev Tools Console and JavaScript functionality:

  • Base64 encode: btoa("string-to-encode")
  • Base64 decode: atob("string-to-decode")
  • URL encode: encodeURIComponent("string-to-encode")
  • URL decode: decodeURIComponent("string-to-decode")
  • HTML encode: escape("string-to-encode")
  • HTML decode: unescape("string-to-decode")

Responsive Design Mode

Google Chrome

  1. Click the Toggle device toolbar button or press ctrl + shift + m.

Responsive Design Mode in Google Chrome
Figure 6.F-8: Google Chrome Responsive Design Mode

Mozilla Firefox

  1. Click the Responsive Design Mode button or press ctrl + shift + m.

Responsive Design Mode in Mozilla Firefox
Figure 6.F-9: Mozilla Firefox Responsive Design Mode

References

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