Abstract. Single Sign-On (SSO) systems simplify login procedures by using an an Identity Provider (IdP) to issue authentication tokens which can be consumed by Service Providers (SPs). Traditionally, IdPs are modeled as trusted third parties. This is reasonable for SSO systems like Kerberos, MS Passport and SAML, where each SP explicitely specifies which IdP he trusts. However, in open systems like OpenID and OpenID Connect, each user may set up his own IdP, and a discovery phase is added to the protocol flow. Thus it is easy for an attacker to set up its own IdP. In this paper we use a novel approach for analyzing SSO authentication schemes by introducing a malicious IdP. With this approach we evaluate one of the most popular and widely deployed SSO protocols -OpenID. We found four novel attack classes on OpenID, which were not covered by previous research, and show their applicability to real-life implementations. As a result, we were able to compromise 11 out of 16 existing OpenID implementations like Sourceforge, Drupal and ownCloud. We automated discovery of these attacks in a open source tool OpenID Attacker, which additionally allows fine-granular testing of all parameters in OpenID implementations. Our research helps to better understand the message flow in the OpenID protocol, trust assumptions in the different components of the system, and implementation issues in OpenID components. It is applicable to other SSO systems like OpenID Connect and SAML. All OpenID implementations have been informed about their vulnerabilities and we supported them in fixing the issues.
Software-as-a-Service (SaaS) is typically defined as a rental model for using a complex software product, running on a centralized computing platform, using a thin client (most frequently a web browser). As such, it is one of the major categories of Cloud Computing, besides IaaS and PaaS.While there are many economic benefits in using SaaS, each company must nevertheless enforce control over its own data processed in the Cloud. One of the most important building blocks of such an enforcement scheme is Identity Management (IdM), whereat the industry standard for IdM is SAML, the Security Assertion Markup Language.In this paper, we study the security of the SAML implementations of 22 SaaS Cloud Providers (SaaS-CPs) and show that 90% of them can be broken, resulting in company data exposure to attackers on the Internet. The detected vulnerabilities are exploited by a wide variety of attack techniques, ranging from classical web attacks to problems specific to XML processing.
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