MAL-2026-12476 Malicious code in tcb-web-header (npm)

On require() of tcb-web-header, platform.js selects an OS/arch-specific endpoint, downloads a binary from Cloudflare workers.dev hosts whose names are reconstructed at runtime by joining split string fragments (e.g. oob-worker.cf99-9b.3.workers.dev, oob-worker.cf100-416.workers.dev, oob-worker.cf101-adf.workers.dev), writes the payload to /var/tmp or %TEMP% under a deceptive name (dotnet_diag<tag>.exe on Windows,.cache_<tag> on Unix), fs.chmodSync to 0o755, and spawns it detached via /bin/sh -c "<path> &" or cmd.exe /c start /b. A base64-encoded chunked DNS TXT retrieval channel over c.<domain>/N.<domain> under tin.dl.well1.site, tina.dl.well1.site, ldr.dl.well1.site, and win.dl.well1.site serves as a covert fallback transport when HTTPS is blocked. The package's declared purpose is a web header helper and there is no build/native-addon rationale for downloading and executing an unverified binary at import time; destination hosts are attacker-controlled, string-reassembled to defeat static scanners, and a token-gated DISABLE_TELEMETRY flag is used as a cover story.

Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.