That's not source code, that's just a config file embedded into the firmware. For most firmware, it's a large binary file that often has different sections cont

That's not source code, that's just a config file embedded into the firmware. For most firmware, it's a large binary file that often has different sections containing stuff like an OS kernel at one spot, a compressed archive somewhere else, etc. For the Cisco firmware in question in the middle of the firmware is a compressed CPIO archive (think of it like a zip file) that contains the root file system. The router is actually a small linux computer, inside that archive they have a config file for nginx (a web server) that tells nginx to return an error if it sees the user agent string for curl. There's no programming required here, just a trivial configuration change that masks the actual issue.