Cross-site Scripting (XSS)

Affecting sinatra gem, versions <1.4.6, >=1.4.0.a

medium severity

Overview

sinatra is a DSL for quickly creating web applications in Ruby with minimal effort.

Affected versions of the package are vulnerable to reflected Cross-site Scripting (XSS). This occurs on the development 404 page, which does not validate the request path. This may allow attackers to create a specially crafted request that would execute arbitrary script code.

Details

Cross-Site Scripting (XSS) attacks occur when an attacker tricks a user’s browser to execute malicious JavaScript code in the context of a victim’s domain. Such scripts can steal the user’s session cookies for the domain, scrape or modify its content, and perform or modify actions on the user’s behalf, actions typically blocked by the browser’s Same Origin Policy.

These attacks are possible by escaping the context of the web application and injecting malicious scripts in an otherwise trusted website. These scripts can introduce additional attributes (say, a "new" option in a dropdown list or a new link to a malicious site) and can potentially execute code on the clients side, unbeknown to the victim. This occurs when characters like \< > \" \' are not escaped properly.

There are a few types of XSS:

  • Persistent XSS is an attack in which the malicious code persists into the web app’s database.
  • Reflected XSS is an which the website echoes back a portion of the request. The attacker needs to trick the user into clicking a malicious link (for instance through a phishing email or malicious JS on another page), which triggers the XSS attack.
  • DOM-based XSS is an that occurs purely in the browser when client-side JavaScript echoes back a portion of the URL onto the page. DOM-Based XSS is notoriously hard to detect, as the server never gets a chance to see the attack taking place.

You can read more about Cross-site Scripting (XSS) on our blog.

Remediation

Upgrade sinatra to version 1.4.6 or higher.

References

Do your applications use this vulnerable package?

Credit
Andy Brody
CWE
CWE-79
Snyk ID
SNYK-RUBY-SINATRA-20469
Disclosed
11 Jun, 2014
Published
10 Jan, 2018