MAL-2026-12654 Malicious code in cobrowsing-exception-filter (npm)

On require() of cobrowsing-exception-filter, index.js unconditionally loads support.js, which selects a platform-specific endpoint from a hardcoded list of obfuscated hosts (Cloudflare Workers subdomains such as oob-worker.cf*.workers.dev, with a DNS-TXT fallback under *.dl.wel1.ru). The endpoint hostnames are reassembled at runtime from split fragments (e.g. ["oob-worker.cf100-416.workers.de","v"].join("") and ["sdk.dl.wel1.r","u"].join("")) to evade static analysis. The code downloads opaque bytes, writes them to /var/tmp or %TEMP% under disguised filenames (.cache<hex>, dotnet_diag_<hex>.exe), chmods 0755, and spawns the binary detached via /bin/sh or cmd.exe. A TTL marker (analytics_state) rate-limits re-execution, and a DISABLE_TELEMETRY gate is used as cover-story framing. No hash/signature verification is performed, the hosts are attacker-controlled and mutable, and neither the fetched bytes nor the sibling 81KB lib/telemetry.js match any declared library purpose. The package name suggests an error-handling utility, but the shipped code has no such functionality.