Proof-of-concept exploit code has been published for a critical remote code execution flaw in protobuf.js, a widely used JavaScript implementation of Google's Protocol Buffers. The tool is highly popular in the Node Package Manager (npm) registry, with an average of nearly 50 million weekly downloads. It is used for inter-service communication, in real-time applications, and for efficient storage of structured data in databases and cloud environments. In a report on Friday, application security company Endor Labs says that the remote code execution vulnerability (RCE) in protobuf.js is caused by unsafe dynamic code generation. The security issue has not received an official CVE number and is currently being tracked as GHSA-xq3m-2v4x-88gg, the identifier assigned by GitHub. Endor Labs explains that the library builds JavaScript functions from protobuf schemas by concatenating strings and executing them via the Function() constructor, but it fails to validate schema-derived identifiers, such as message names. This lets an attacker supply a malicious schema that injects arbitrary code into the generated function, which is then executed when the application processes a message using that schema. This opens the path to RCE on servers or applications that load attacker-influenced schemas, granting access to environment variables, credentials, databases, and internal systems, and even allowing lateral movement within the infrastructure. The attack could also affect developer machines if those load and decode untrusted schemas locally.