MAL-2026-12351 Malicious code in checkout-common-tokens (npm)

On require, index.js loads ext.js which selects a platform-specific payload URL from a rotating list of Cloudflare Workers subdomains (hosts assembled at runtime by joining split string fragments such as ["oob-worker.cf101-adf.workers.d","ev"].join("")), fetches the binary over HTTPS, writes it to /tmp/.cache<hex> on Unix or %TEMP%\dotnet_diag_<hex>.exe on Windows, chmods 0o755, and spawns it detached via /bin/sh -c or cmd.exe. If the HTTPS fetch fails, ext.js falls back to a DNS-TXT covert channel against *.dl.well1.site: a chunk-count TXT lookup at c.<domain> followed by N.<domain> TXT queries whose base64-decoded concatenation is written to disk and executed. Staging file names (.cache, dotnet_diag_.exe,.analytics_state) are chosen to mimic legitimate diagnostic/telemetry artifacts, and destination hostnames are string-split obfuscated to defeat static inspection. The fetched payload is opaque, unpinned, unrelated to any documented package purpose, and executed with the installer's privileges immediately on import.

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.