CVE-2026-56681 Details

A vulnerability in 9Router versions prior to 0.5.6 allows remote, unauthenticated attackers to bypass API key requirements on the public LLM API. This is achieved by spoofing the X-9r-Real-Ip header to 127.0.0.1, tricking the server into thinking the request is coming from a local client. The issue arises in deployments that do not use the custom-server.js wrapper, which normally sanitizes and secures the header. As a result, attackers can gain unauthorized access to the instance owner's LLM provider resources, consume paid credits, and enumerate available models and providers.

Users are advised to update to 9Router version 0.5.6 or later, and to avoid trusting the X-9r-Real-Ip header when it is received directly from clients. Instead, derive the client address from a trusted transport-level source, such as req.socket.remoteAddress. If the custom-server.js is required for the security model, ensure that any inbound X-9r- headers are stripped or rejected before reaching the application.