The following unauthenticated Client-Side Template Injection (CSTI) resulting in a Cross-Site Scripting (XSS) vulnerability was discovered in a private bug bounty program. While the vulnerability could only be exploited in case a user had no active session at the application, chained with an SSO gadget, a malicious actor could have still gained access to the user’s account and performed actions on behalf of the user.

With the rise of Single-Sign-On (SSO) and especially OAuth 2.0 and OpenID Connect (OIDC), the attack surface of web applications has increased significantly. In this post, I will show how to escalate a Cross-Site Scripting (XSS) vulnerability to an Account Takeover (ATO) by abusing OAuth2/OIDC gadgets and how to prevent such attacks.

The Auth. Request Analyser (AuRA) Chromium extension aims to support the analysis of OAuth and OpenID Connect implementations, by offering semi-automated analysis and attack capabilities for Authorization/Authentication Requests.

During my master’s thesis, I created custom OpenID Connect Service Provider (SP) and Identity Provider (IdP) implementations for research and Proof-of-Concept purposes. Both implementations use NodeJS. This post outlines their capabilities and how they can be extended.

In this post, I will discuss an OAuth 2.0 and OpenID Connect 1.0 implementation flaw pattern that was or is present even in well-known implementations from Github, Stackoverflow and Microsoft.