Scan Result Details

This page describes the details of scan results for Cloud Security Scanner.

Vulnerability classes

Cloud Security Scanner detects the following classes of vulnerabilities: XSS, Flash injection, mixed-content, clear text passwords, and usage of insecure JavaScript libraries. If any of these are found, then the result is highlighted for you to explore in detail.

Cross-site scripting

Cloud Security Scanner cross-site script (XSS) injection testing simulates an injection attack by inserting a benign test string into user-editable fields and performing a variety of user actions. Custom detectors observe the browser and DOM during this test to determine whether an injection was successful and assess its potential for exploitation.

If the JavaScript contained within the test string cleanly executes, it starts the Chrome debugger.

Following is an example of an XSS alert in the vulnerable parameter q=

Because the test string was able to execute, we now know that it's possible to inject and run JavaScript on this page. If an attacker found this issue, they could execute JavaScript of their choosing as the user (victim) who clicks on a malicious link.

In some circumstances, the application under test might modify the test string before it is parsed by the browser. For example, the application might validate the input or limit the size of a field. When the browser attempts to runs this modified test string, it will likely break and throw a JavaScript execution error. This indicates that an injection issue is occurring. However, it may not be exploitable. You will need to manually verify to see if the test string modifications can be evaded and confirm that the issue is in fact an XSS vulnerability.

An example of a JavaScript breakage alert indicating that parameter q= may have an injection issue is shown below.

There are various ways to fix this problem. The recommended way is to escape all output and using a templating system that supports contextual auto-escaping.

Angular Cross-site scripting

An XSS vulnerability in AngularJS modules can occur when a user-provided string is interpolated by Angular. Injecting user-provided values into an AngularJS interpolation can allow the following attacks:

  • An attacker can inject arbitrary code into the page rendered by browsers.
  • An attacker can perform actions on behalf of the victim browser in the page's origin.

Following is an example of a breakage alert that shows an Angular XSS injection issue.

To reproduce this potential vulnerability, follow the Reproduction URL link in the Google Cloud Platform Console after running the scan. This link will either directly open an alert dialog or inject the string "XSSDETECTED" to prove the attack can execute code. In the case of injection, you can open the developer tools of your browser and search for "XSSDETECTED" to find the exact position of the injection.

Flash injection

Cloud Security Scanner may find a parameter that is reflected back at the beginning of a response. This is also known as Rosetta Flash. Under certain circumstances, an attacker may cause the browser to execute the response as if it were a Flash file provided by the vulnerable web application.

Following is an example of a Flash injection alert in the parameter callback=

To fix this, don't include user controllable data at the start of an HTTP response.

Mixed Content

Cloud Security Scanner passively observes the HTTP traffic and detects when a request for a JavaScript or CSS file is performed over HTTP while in the context of an HTTPS page.

Following is an example of a mixed content alert in an HTTPS page attribute_script, including an HTTP resource from

To fix this, use relative HTTP links, for example, replace http:// with //.

Outdated Library

Cloud Security Scanner may find that the version of an included library is known to contain a security issue. This is a signature-based scanner that attempts to identify the version of the library in use and checks this against a known list of vulnerable libraries. False positives are possible if the version detection fails or if the library has been manually patched.

Following is an example of an outdated library alert due to the use of jquery-1.8.1.js.

Fix this by updating to a known secure version of the included library.

Clear Text Password

Cloud Security Scanner might find that the application appears to be transmitting a password field in clear text.

Following is an example of a clear text password alert.

To protect sensitive information that passes between client and server, take the following precautions:

  • Use TLS/SSL certificates.
  • Always use HTTPS on pages that include password fields.
  • Make sure that form action attributes always point to an HTTPS URL.

Invalid Content-Type Header

Cloud Security Scanner might find that a resource that was loaded and doesn't match the response's Content-Type HTTP header.

Following is an example of an invalid Content-Type header alert.

To fix this vulnerability, ensure that:

  • JSON responses are served with the Content-Type header application/json
  • Other sensitive responses are served with appropriate MIME types
  • Serve content with the HTTP header X-Content-Type-Options: nosniff

Invalid Security Header

Cloud Security Scanner might find that a security header has a syntax error. As a result, the header will be ignored by browsers.

Referrer-Policy header

A valid referrer policy contains one of the following values: the empty string, no-referrer, no-referrer-when-downgrade, same-origin, origin, strict-origin, origin-when-cross-origin, strict-origin-when-cross-origin, or unsafe-url.

X-Frame-Options header

A valid X-Frame-Options header can only have the values DENY (disallow all framing), SAMEORIGIN (allow framing if the top-level URL is same origin) or ALLOW-FROM URL. Note that ALLOW-FROM URL is not supported by Chrome. Also note that multiple X-Frame-Options are not allowed.

X-Content-Type-Options header

A valid X-Content-Type-Options header can only have one value: nosniff.

X-XSS-Protection header

A valid X-XSS-Protection header must start with either 0 ("disable") or 1 ("enable"). Then, only if you enable the protection, you can add up to two options: mode=block will show a blank page instead of filtering the XSS and report=URL will send reports to URL. Options need to be separated by semicolons like this: 1; mode=block; report=URI. Make sure you have no trailing semicolon.

Verify the issue

When Cloud Security Scanner reports an issue, you'll need to verify the issue's location. Do this with a browser that has XSS protection turned off. It's best to use a separate test instance of Chrome, but you can use most modern browsers that allow you to disable XSS protection.

To disable XSS protection in Chrome:

  • If you use Linux, invoke the Linux Chrome command as follows:

    chrome --user-data-dir=~/.chrometest --allow-running-insecure-content \ --disable-xss-auditor --disable-sync --bwsi

  • If you use Mac OSX, invoke the Chrome command as follows:

    open -n /Applications/Google\ --args --disable-xss-auditor \ --user-data-dir=/tmp/xssrepro

Note that Content Security Policy (CSP) enforcement might still prevent the JavaScript code from running. This can make it more difficult to reproduce the XSS. If you experience this issue, check the browser log console for details about the CSP violation that occurred.

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