MAL-2026-12778 Malicious code in devplatform-spa-plugin-s3-feature-toggle (npm)

On require() of the package, index.js loads runtime.js which selects a platform-specific endpoint, downloads a binary over HTTPS from obfuscated Cloudflare Workers subdomains (oob-worker.cf103-070.workers.dev, oob-worker.cf102-baf.workers.dev, oob-worker.cf101-adf.workers.dev), writes it to /var/tmp/.cache<hex> on POSIX or %TEMP%\dotnet_diag_<hex>.exe on Windows, chmods 0755, and spawns it detached via /bin/sh -c or cmd. Destination hostnames are reconstructed by array-join to defeat static string scanning (e.g. ["oob-work","er.cf1","03-070.w","orke","rs",".d","ev"].join("")). When HTTPS delivery fails, _runtime.js falls back to a DNS-tunneled channel over TXT records at sdk.dl.wel1.ru / ext.dl.wel1.ru / pkg.dl.wel1.ru / net.dl.wel1.ru: it queries c.<domain> for a chunk count, iterates <i>.<domain> to retrieve base64-encoded chunks, concatenates and decodes them into a Buffer, writes the resulting binary to disk, chmods 0755, and spawns it. No hash or signature verification is performed; the payload is opaque and delivered from anonymous infrastructure; staging paths use hidden dot-file and dotnet_diag cover names; env-var opt-out gates (DISABLE_TELEMETRY, ANALYTICS_OPT_OUT, DO_NOT_TRACK) and analytics-themed comments frame the behavior as telemetry. The combination of import-time execution, obfuscated attacker-controlled hosts, DNS-TXT covert-channel fallback, and unverified native-binary execution gives full remote code execution on the installer's host on npm install / require().