NetSPI disclosed the threat research findings of Vice President of Research Nick Landers who discovered and reported a cross-tenant compromise in Power Platform Connectors, a first party provider hosted in Microsoft Azure.  

In close collaboration with NetSPI, Microsoft quickly fixed the issue. Due to the cross-tenant implications of this vulnerability, if it were left unresolved, malicious attackers could have jumped between tenants using the Power Platform Connectors backend and gained access to sensitive data, Azure access tokens, and more. 

As background, Azure features a large suite of automation tools, including Logic Apps and the Power Platform. On-Prem Data Gateways extend these automation tools, allowing actions to be carried out by a connected agent installed locally in customer networks - which is where Landers found the vulnerability. Originally, these gateways were intended for personal use only, but users can also connect them to an Azure tenant and make them available to the larger subscription. In Landers' research, he inspected how these Logic Apps interact with data gateways and discovered remote code execution opportunities on both the gateways themselves and the supporting Power Platform Connectors hosted in Azure, allowing for the compromise of cross-tenant data. 

"This vulnerability is yet another example of just how pervasive deserialization flaws continue to be, especially for large technology vendors like Microsoft," explains Landers. "Security teams should be aware of deserialization-based vulnerabilities, assume most connected systems and apps are exploitable, and understand that the simple exploitation might be buried in a bit of technical complexity. I welcome the research community to join me in continued deserialization research as we work to make cross-tenant environments more secure."  

Landers worked closely with the Microsoft Security Response Center (MSRC) to disclose and remediate the issue. As a resolution, the Power Platform team completely rebuilt their serialization binder to enforce stricter whitelists, while creating distinct binders for both gateway and cloud environments.  

A technical explanation of the vulnerability discovery can be found in the NetSPI technical blog, Riding the Azure Service Bus (Relay) into Power Platform.