tcb-web-header@20.5.7

Analysis

tcb-web-header@20.5.7 is a combosquat binary dropper. On require(), _platform.js runs a bootstrap that fingerprints the OS/arch, then fetches a platform-specific binary from Cloudflare Workers C2 endpoints (oob-worker[.]cf99-9b3[.]workers[.]dev, oob-worker[.]cf100-416[.]workers[.]dev, oob-worker[.]cf101-adf[.]workers[.]dev) via HTTPS GET /pkg/package (or /pkg/package-arm64, /pkg/loader_mac, /pkg/package.exe per platform). If HTTPS fails, it falls back to DNS TXT chunked transfer via c[.]tin[.]dl[.]well1[.]site. The downloaded binary is written to /var/tmp/.cache_<hex> (Linux/macOS) or %TEMP%\dotnet_diag_<hex>.exe (Windows) and spawned as a detached background process (cmd.exe /c start /b on Windows, /bin/sh -c on Unix). All three C2 hosts were contacted at runtime and the binary was fetched.