Careful Who You Trust: Studying the Pitfalls of Cross-Origin Communication

Gordon Meiser (1) , Pierre Laperdrix (2) , Ben Stock (1)

1 CISPA - Helmholtz Center for Information Security [Saarbrücken]
2 SPIRALS - Self-adaptation for distributed services and large software systems

In the past, Web applications were mostly static and most of the content was provided by the site itself. Nowadays, they have turned into rich client-side experiences customized for the user where third parties supply a considerable amount of content, e.g., analytics, advertisements, or integration with social media platforms and external services. By default, any exchange of data between documents is governed by the Same-Origin Policy, which only permits to exchange data with other documents sharing the same protocol, host, and port. Given the move to a more interconnected Web, standard bodies and browser vendors have added new mechanisms to enable cross-origin communication, primarily domain relaxation, postMessages, and CORS. While prior work has already shown the pitfalls of not using these mechanisms securely (e.g., omitting origin checks for incoming postMessages), we instead focus on the increased attack surface created by the trust that is necessarily put into the communication partners. We report on a study of the Tranco Top 5,000 to measure the prevalence of cross-origin communication. By analyzing the interactions between sites, we build an interconnected graph of the trust relations necessary to run the Web. Subsequently, based on this graph, we estimate the damage caused through exploitation of existing XSS flaws on trusted sites.

Domaines: Web; Cryptographie et sécurité [cs.CR]; Informatique [cs]

Gordon Meiser, Pierre Laperdrix, Ben Stock. Careful Who You Trust: Studying the Pitfalls of Cross-Origin Communication. ASIACCS 2021 - 16th ACM Asia Conference on Computer and Communications Security, Jun 2021, Hong Kong / Virtual, China. ⟨hal-03021256⟩