Cloud security often makes headlines for sophisticated breaches, but sometimes the biggest risks come from the simplest mistakes. One such case emerged when a publicly accessible JSON configuration file (appsettings.json) leaked Azure Active Directory (AD) credentials, giving attackers the potential to waltz straight into Microsoft's cloud ecosystem.
This wasn't just a small oversight. The exposure of these secrets meant that anyone on the Internet — from opportunistic bots to advanced threat actors — could impersonate trusted applications and gain direct access to sensitive data across Azure environments.
How the Leak Was Discovered
Researchers from Resecurity's HUNTER team stumbled upon the issue during routine analysis. The credentials they found — specifically the ClientId and ClientSecret for Azure AD — were sitting inside an appsettings.json file, publicly accessible online.
These two values are critical. Together, they allow an attacker to authenticate against Microsoft's OAuth 2.0 endpoints, effectively masquerading as a legitimate application. In practical terms, this is like handing out the master key to a corporate office tower, complete with access to every floor and room.
Why Appsettings.json Is So Sensitive
In ASP.NET Core applications, appsettings.json is the central configuration file. Developers rely on it to store everything the application needs to function, such as:
The problem? Many of these values are sensitive. Expose them, and you expose the entire application ecosystem.
As Resecurity's researchers put it, this file can act as the blueprint of the application — not only explaining how it connects to services but sometimes holding the very credentials that make those connections possible.
How Attackers Could Exploit the Leak
With valid credentials in hand, a threat actor could launch a wide range of attacks. Using the OAuth2 Client Credentials flow, they could obtain access tokens and query the Microsoft Graph API. From there, the possibilities open up:
In short, what looks like a minor misconfiguration could escalate into a complete tenant compromise.
Why Secrets Exposure Keeps Happening
This case highlights a common problem: poor secrets management. Developers often hardcode secrets — ClientIds, ClientSecrets, database passwords — directly into config files for convenience. While this might work in a local environment, it becomes a critical vulnerability when the file is exposed to the public Internet.
Attackers know this. They actively scan for exposed configuration files using tools like dirsearch, automated crawlers, and GitHub repo scans. What developers think of as obscure files are, in reality, low-hanging fruit for cybercriminals.
Best Practices to Prevent Azure Secrets Exposure
The good news? Preventing this type of leak is not rocket science. Organizations can significantly reduce the risk by following a few key steps:
Final Thoughts
The Azure AD credentials leak is a stark reminder that cloud security is only as strong as its weakest link. In this case, that weak link was a single JSON file.
As organizations continue migrating workloads to the cloud, configuration files will remain an attractive target for attackers. By treating secrets like the crown jewels they are — and storing them in secure vaults instead of plaintext files — businesses can avoid handing adversaries the keys to their cloud kingdom.
