2025-10-23 –, Europe
There is a widespread belief that services that are only bound to localhost are not accessible from the outside world. Developers for convenience sake will run services they are developing configured in a less secure way compared to how they would (hopefully!) do in higher environments.
By compromising websites developers use, just injecting JS into adverts served on those sites or just a phishing attack that gets the developer to open a web browser on a compromised page, it is possible to reach out via non pre-flighted http requests to those services bound to localhost, by exploiting common misconfigurations in Spring, or known vulnerabilities found by myself and others. I’ll demonstrate during the talk, it is possible to generate a RCE on the developer’s machine or other services on their private network.
As developers have write access to codebases, AWS keys, server creds etc., access to the developer’s machine gives an attacker a great deal of scope to pivot to other resources on the network, modify or just steal the codebase.
The talk will go into detail about the underlying issues with this vulnerability type. How it is possible for Javascript loaded from a website can access localhost. What limitations there are and how this feature can be used to attack unsuspecting users, especially software developers. Including a way to gain Remote Code Execution on Quarkus ( a popular Java Web framework ) Developers machines and older versions of Spring and a way to exfiltrate AI Training models from users of the popular machine learning software MLFlow, all found by me and there are likely many more similar issues out there.
Also what browser makers are doing about this class of vulnerability and how it will soon be no more, but for now is still a major, but relatively unknown attack vector.
I'm a recovering Java Developer. I started my career as a Java developer writing Archive/Backup software before moving to a large financial company working on webapps and the backend APIs. However, after a while, writing yet another microservice isn't that much fun anymore but breaking them was. So, I moved to Application Security and from there to research. I now work as a Staff Application Security Researcher for Contrast Security.