MAL-2026-17581 Malicious code in bip39-wordlist-utils (RubyGems)

RubyGems runs this gem's native extension script ext/bip39-wordlist-utils/extconf.rb during gem install. The script exits without action on CI runners and sandboxes, based on CI environment variables, the hostname, the username and the working directory. It continues if the system uptime is over 30 minutes and the home directory holds .ssh, .gitconfig, .npmrc, .gem/credentials or .bundle. It then decodes a Base64 Ruby payload and forks twice into a detached process. After 20 to 40 minutes the payload downloads http://45.138.12.177:8092/wgkit.tar.gz to /tmp/.w1.tgz with curl, extracts it to /tmp/.w1/, runs wg_install.sh with bash and deletes both. The payload stores the URL XOR-encoded with the key usv\x9a. The Ruby code in lib/ is a decoy. The RubyGems account reqthrottle_3474 published this gem and 41 others with the same loader on 2026-10-05.

The gem declares a native C extension whose shipped source (ext/bip39-wordlist-utils/bip39-wordlist-utils.c) is an empty Init stub, so gem install executes extconf.rb purely as a lifecycle hook. extconf.rb decodes a base64 Ruby blob and evals it; the eval'd payload XOR-reconstructs the URL http://45.138.127.177:8092/wgkit.tar.gz (bare IP, plain HTTP, unrelated to any BIP39 purpose), double-forks a detached child, uses curl to download the tarball to /tmp/.w1.tgz, extracts to /tmp/.w1, and executes wg_install.sh as the installing user. Execution is gated by developer-targeting evasion checks: it aborts when CI env vars are set, when hostname matches sandbox/firecracker/vagrant, when the username matches scanner/analys/sandbox/tester, when CWD is under /tmp, /var/tmp, /opt/rubygems, or /workspace, or when /proc/uptime is under 1800 seconds, and only proceeds when developer artifacts (~/.ssh, ~/.gitconfig, ~/.gem/credentials, ~/.bundle, ~/.npmrc) are present. The payload then sleeps 1200-2400 seconds before firing. After the dropper logic, extconf.rb calls create_makefile to let the gem install appear to succeed. No legitimate build toolchain probing (mkmf have_header, pkg_config, try_run) is performed and no real native source is compiled.