Microsoft Token Brokering and Dev Tunnels Enable Cross-Service Remote Access

Researchers detailed how Microsoft nested app authentication (NAA), also called BroCI, can let an attacker who already holds a valid refresh token from a broker-capable Microsoft application exchange it for tokens to other apps and resources. The technique was shown against Azure and Entra ID workflows to retrieve Conditional Access Policy data, activate Privileged Identity Management roles, access Azure Key Vault secrets, and enumerate Intune devices by brokering requests through administrator portals. The write-up emphasized that MFA claims present in the original broker token can persist into downstream requests, potentially satisfying Conditional Access checks, and clarified that the method relies on refresh tokens, not access tokens.

A separate offensive analysis showed that VS Code Dev Tunnels can be abused for remote access by using authenticated GitHub or Azure/Entra ID tokens to enumerate tunnels, obtain connect-scoped JWTs, establish WebSocket relay sessions, and invoke MsgPack-based RPC methods for command execution and file operations on tunnel hosts. The author said credentials stored by VS Code can still be recovered by same-user processes despite Electron safeStorage, and released a Rust proof-of-concept called Ouroboros to interact with existing tunnels. Together, the research highlights how token theft, device-code phishing, and Microsoft token pivoting techniques such as FOCI/BroCI can extend access across cloud administration surfaces and developer remote-access infrastructure.