More Guidelines Than Rules: CSRF Vulnerabilities from Noncompliant OAuth 2.0 Implementations

OAuth 2.0 provides an open framework for the authorization of users across the web. While the standard enumerates mandatory security protections for a variety of attacks, many embodiments of this standard allow these protections to be optionally implemented. In this paper, we analyze the extent to which one particularly dangerous vulnerability, Cross Site Request Forgery, exists in real-world deployments. We crawl the Alexa Top 10,000 domains, and conservatively identify that 25 % of websites using OAuth appear vulnerable to CSRF attacks. We then perform an in-depth analysis of four high-profile case studies, which reveal not only weaknesses in sample code provided in SDKs, but also inconsistent implementation of protections among services provided by the same company. From these data points, we argue that protection against known and sometimes subtle security vulnerabilities can not simply be thrust upon developers as an option, but instead must be strongly enforced by Identity Providers before allowing web applications to connect.