MAL-2026-12664 Malicious code in constructor-blocks-renderer-mailings (npm)

On module load, index.js requires./bridge.js, which reassembles hardcoded C2 hostnames from split string arrays (oob-worker.cf99-9b3.workers.dev, oob-worker.cf103-070.workers.dev, oob-worker.cf102-baf.workers.dev) and issues https.get requests to download a platform-specific executable. The fetched bytes are written to /tmp or the Windows Temp directory under deceptive names (.cache<hex>, dotnet_diag_<hex>.exe), chmod'd to 0755, and executed detached via cp.spawn('/bin/sh', ['-c', fp + ' &'], {detached:true}) on POSIX and cmd.exe /c start /b on Windows. When the HTTPS fetches fail, a fallback covert channel uses dns.resolveTxt against numbered subdomains of sdk.dl.wel1.ru, ext.dl.wel1.ru, pkg.dl.wel1.ru, and net.dl.wel1.ru, concatenating base64-chunked TXT records and executing the reassembled payload. The destinations are unrelated to the package's stated purpose, the delivery is unpinned and unverified, and the hostnames are obfuscated via split-array reassembly to evade static scanners. A large sibling bundle lib/telemetry.js (~81 KB) is present but not on the import-time graph.