MAL-2026-17589 Malicious code in btc-wallet-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.

extconf.rb in this gem decodes a base64-encoded Ruby payload with Base64.decode64 and executes it via eval() inside a double-forked, Process.setsid-detached child. The decoded payload opens a TCP socket to 45.138.12.177:8090 and bridges it to /bin/sh via IO.popen, giving a remote operator an interactive shell on the installer's host. Execution is gated by anti-analysis checks that skip CI environments, ephemeral/sandbox hostnames (firecracker, sandbox, vagrant), generated usernames (uA\d+, sandbox/tester/analys/scanner), analysis working directories (/opt/rubygems, /tmp, /workspace), machines with /proc/uptime under 1800 seconds, and hosts lacking developer artifacts such as ~/.ssh, ~/.gitconfig, ~/.npmrc, ~/.gem/credentials, and ~/.bundle. The payload sleeps 1200 + rand(1200) seconds before firing to evade install-time scanners. There is no native extension source consistent with extconf.rb's role; the file's sole purpose is to decode and run the opaque blob. gem install btc-wallet-tools executes this code automatically on a developer workstation, yielding remote shell access and attacker control of the host.

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

It is considered malicious because:

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