MAL-2026-17585 Malicious code in bitcoij-ruby (RubyGems)

RubyGems runs this gem's native extension script ext/bitcoij-ruby/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 extension (ext/bitcoij-ruby/extconf.rb) whose matching C source is an empty 50-byte Init function, so the extension exists solely to run extconf.rb during gem install. extconf.rb base64-decodes a Ruby snippet and eval()s it inside a double-forked, detached child. The decoded payload reconstructs a hardcoded C2 URL via XOR-obfuscated hex bytes resolving to http://45.138.129.177:8092/wgkit.tar.gz, downloads the archive to /tmp over plain HTTP with no integrity check, extracts it, and executes bash /tmp/.w1/wg_install.sh on the installer's machine. Execution is gated by sandbox/analysis evasion checks that skip CI environments, ephemeral hostnames (firecracker/sandbox/vagrant), generated usernames, analysis cwd prefixes (/tmp, /var/tmp, /opt/rubygems, /workspace), hosts with uptime under 1800 seconds, and hosts lacking developer-credential paths (~/.ssh, ~/.gitconfig, ~/.gem/credentials, ~/.bundle, ~/.npmrc); it also sleeps 1200+rand(1200) seconds before firing. The gem is advertised as a pure-Ruby Bitcoin/BIP-39 helper with no legitimate reason to probe developer credential stores or fetch remote shell scripts.