MAL-2026-12559 Malicious code in checkout-desktop-pay-widget (npm)

On require('checkout-desktop-pay-widget'), index.js loads shim.js which selects a platform-specific asset, downloads an opaque native binary from one of four runtime-assembled Cloudflare Workers hosts (oob-worker.cf99-9b3.workers.dev / cf100-416.workers.dev variants), writes it to /tmp or %TEMP% under decoy names (.cache<hex> on POSIX, dotnet_diag_<hex>.exe on Windows), chmods 0755, and spawns it detached via /bin/sh -c or cmd.exe. Destination hostnames are split into fragments and joined at runtime to evade static string scanning. A DNS-TXT fallback channel resolves TXT records under sdk.dl.wel1.ru, ext.dl.wel1.ru, pkg.dl.wel1.ru, and net.dl.wel1.ru, concatenates chunks, base64-decodes the result to executable bytes, and runs them — a covert payload-retrieval channel that bypasses HTTP egress controls. No signature or hash verification is performed. Function names (bootstrap/telemetry, DISABLE_TELEMETRY,.analytics_state lock file) present a benign cover story that conflicts with the fetch-write-chmod-exec chain. Package name mimics a checkout/payment widget but the shipped code implements a full-host remote code execution dropper.