MAL-2026-13233 Malicious code in bigops-procedure-file-handlers (npm)

On require of the package, runtime.js downloads a platform-specific executable from obfuscated Cloudflare Workers endpoints (hostnames reassembled at runtime via array-join, e.g. oob-worker.cf99-9b3.workers.dev and sibling cf101/cf103/cf100 workers), writes it to /tmp or %TEMP% under a cover-story filename (dotnet_diag<tag>.exe on Windows,.cache_<tag> on Unix), chmods it to 0755, and detached-spawns it via /bin/sh -c or cmd.exe /c start /b. If HTTPS delivery fails, a fallback path queries DNS TXT records at subdomains of *.dl.wel1.ru, reads a chunk count from c.<host>, reassembles base64 chunks from N.<host> TXT records, and executes the resulting buffer. A stamp file.analytics_state is written to disguise the drop as OS/telemetry state. The obfuscation of destinations, covert DNS-TXT delivery channel, and disguised filenames indicate intentional evasion rather than legitimate telemetry or binary distribution.