Pentester Builds Custom Traffic Listener After Burp Suite Fails on Unstable VPN App

A security researcher encountered persistent proxy failures while pentesting an internal financial web app for a student loan servicer, with Burp Suite, Caido, and other tools all failing to capture traffic reliably. The app exhibited an unusual pattern where requests would succeed briefly, then time out for up to an hour, and any modified request — such as one containing a quote or script tag — would receive no response at all. After three largely unproductive days, the researcher concluded that the unstable connection was being worsened by a man-in-the-middle proxy decrypting and resending traffic. Instead of intercepting requests, they built a lightweight browser extension that captures outgoing traffic and immediately forwards it to a local listener program, avoiding the performance issues of storing data in localStorage. The solution resolved both the CORS preflight problem and browser slowdowns by keeping the extension stateless and offloading all storage to the local listener.