MAL-2026-17595 Malicious code in crypto-mnemonic-tools (RubyGems)

RubyGems runs this gem's native extension script ext/req_throttle_mini/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, forks twice into a detached process, waits 20 to 40 minutes and opens a reverse shell that connects /bin/sh to 45.138.12.177 on TCP port 8090. The shell reconnects every 30 seconds. 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 advertises itself as a BIP-39 mnemonic helper but ships an ext/req_throttle_mini/extconf.rb native-extension script with no C sources alongside it. On gem install, the extconf.rb decodes a base64 Ruby payload and evals it inside a detached, double-forked daemon that opens a TCPSocket to 45.138.12.177:8090 and bridges it to /bin/sh via IO.popen(['/bin/sh'], 'r+') and an IO.copy_stream loop, giving a remote operator interactive shell on the installer's host. Process.setsid, double fork, Process.detach, and reopening std streams to /dev/null background the shell so the install completes normally. Execution is gated by anti-analysis checks that skip CI environments (CI, GITHUB_ACTIONS, TRAVIS, JENKINS_URL, GITLAB_CI, CODESPACES), ephemeral/sandbox hostnames (uvm, firecracker, sandbox, vagrant), generated/analyst usernames, analysis working directories (/opt/rubygems, /tmp, /var/tmp, /workspace), and hosts with uptime under 1800 seconds, and additionally requires developer artifacts (~/.ssh, ~/.gitconfig, ~/.npmrc, ~/.gem/credentials, ~/.bundle) to be present before firing. The script then sleeps 1200+rand(1200) seconds before connecting to delay the egress past install-time monitoring. The extconf.rb calls create_makefile('crypto_mnemonic_tools_native') as a stub with no accompanying native source, so the extension exists solely as an install-time execution vector. The lure name targets developers handling crypto wallet mnemonics, whose workstations are the gated-for target.

The OpenSSF Package Analysis project identified 'crypto-mnemonic-tools' @ 1.0.0 (rubygems) as malicious.

It is considered malicious because:

• The package executes one or more commands associated with malicious behavior.