Cross-site Scripting (XSS)

Affecting foundation-sites package, versions <6.0.0

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Overview

foundation-sites is an advanced responsive front-end framework.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) attacks due to an insufficient fix to npm:foundation-sites:20150619

Thanks to Nathaniel Paulus for disclosing this vulnerability!

Although innerHTML does not make script tags executable, script tags are not the only way to run arbitrary code.

This vulnerability was introduced in a deliberate attempt to allow HTML in captions. The file was subsequently deleted when version 6 was merged into the develop branch in 1e08494bb2118c9786ffc33c28158311cd542bcb. Confirmation of its removal (as well as plans to re-add it) can be found in issue 7759

Details

A cross-site scripting attack occurs when the attacker tricks a legitimate web-based application or site to accept a request as originating from a trusted source.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

ֿInjecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Type Origin Description
Stored Server The malicious code is inserted in the application (usually as a link) by the attacker. The code is activated every time a user clicks the link.
Reflected Server The attacker delivers a malicious link externally from the vulnerable web site application to a user. When clicked, malicious code is sent to the vulnerable web site, which reflects the attack back to the user’s browser.
DOM-based Client The attacker forces the user’s browser to render a malicious page. The data in the page itself delivers the cross-site scripting data.
Mutated The attacker injects code that appears safe, but is then rewritten and modified by the browser, while parsing the markup. An example is rebalancing unclosed quotation marks or even adding quotation marks to unquoted parameters.

Affected environments

The following environments are susceptible to an XSS attack:

  • Web servers
  • Application servers
  • Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

  • Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
  • Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
  • Give users the option to disable client-side scripts.
  • Redirect invalid requests.
  • Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
  • Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
  • Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Disclosure Timeline

  • March 14th, 2017 - Responsible Disclosure and PoC sent by Nathaniel Paulus.
  • April 13th, 2017 - Disclosure to first contact @foundation-sites
  • May 14th, 2017 - Disclosure to first and secondary contacts @foundation-sites
  • June 12th, 2017 - After no response from either contact, PoC sent to both contacts.
  • August 2nd, 2017 - Vulnerability made public.

Remediation

Upgrade foundation-sites to version 6.0.0 or higher.

CVSS Score

6.5
medium severity
  • Attack Vector
    Network
  • Attack Complexity
    Low
  • Privileges Required
    None
  • User Interaction
    None
  • Scope
    Unchanged
  • Confidentiality
    Low
  • Integrity
    Low
  • Availability
    None
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N/E:F/RL:O/RC:C
Credit
Nathaniel Paulus
CWE
CWE-79
Snyk ID
npm:foundation-sites:20170802
Disclosed
01 Aug, 2017
Published
02 Aug, 2017