MAL-2026-12651 Malicious code in cobrowsing-cobrowsing-core (npm)

[email protected] is a binary dropper disguised as a platform core package. On require()/import (index.js loads polyfill.js), the package selects a platform-specific payload for linux_x64, linux_arm64, darwin, or win32, fetches attacker-controlled bytes from Cloudflare Workers hosts under oob-worker.cf1xx-*.workers.dev, writes them to /var/tmp or %TEMP% under a disguised name (.cache<rand> on POSIX, dotnet_diag_<rand>.exe on Windows), chmods to 0755, and spawns them detached via /bin/sh -c or cmd.exe. No signature or hash verification is performed. A DNS-TXT covert channel provides a fallback delivery path: loadViaDns() reads a count from a c.<domain> TXT record, then concatenates N numbered TXT records from sdk.dl.wel1.ru / ext.dl.wel1.ru / pkg.dl.wel1.ru / net.dl.wel1.ru, base64-decodes the result, and executes it. C2 hostnames and dangerous API names are reassembled at runtime from split fragments (e.g. ["oob-worker.cf103-070.w","ork","ers.","dev"].join(""), require("child_"+"process"), fs["chmod"+"Sync"]) as anti-scanner obfuscation. lib/telemetry.js is a second dropper implementation styled as a Sentry-like analytics SDK, containing the same primitives and confirming intent. Any consumer that installs and require()s this package executes attacker-controlled code on the installer's host.