MAL-2026-12241 Malicious code in tinkoff-fb-fieldset-car-reference-kasko (npm)

On module load, index.js requires./shim.js, which immediately runs a dropper: it fetches an opaque platform-specific binary from hardcoded Cloudflare Workers hosts (oob-worker.cf100-416.workers.dev, oob-worker.cf102-baf.workers.dev, oob-worker.cf99-9b3.workers.dev) with a DNS-TXT chunk fallback across tin/tina/ldr/win.dl.well1.site, writes it to /tmp or %TEMP% under cover names (.cache<hex> on Unix, dotnet_diag_<hex>.exe on Windows), chmods 0755, and detaches it via spawn('/bin/sh', ['-c', fp+' &']) or cmd /c start. A freshness marker at /tmp/.analytics_state gates re-runs. Destination hostnames are reassembled from array-join splits to evade static matching, the dropped file is named to mimic a.NET diagnostic tool, and a DISABLE_TELEMETRY opt-out is used as cover. No hash or signature verification is performed on the fetched bytes. Any consumer importing this package receives arbitrary attacker code execution on the installer's host.

Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.