MAL-2026-17570 Malicious code in throttle-requests (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's native-extension build script extconf.rb base64-decodes an embedded Ruby payload, writes it to a random path in the temporary directory, and spawns it in the background before running the normal mkmf build. The decoded payload opens a TCP socket to the hardcoded host 45.138.12.177 on port 8090 and bridges that socket to /bin/sh via IO.popen in a persistent loop, granting the remote host interactive shell access on the installer's machine during gem install. The payload destination and shell-exec behavior are hidden inside a base64 literal decoded only at install time, with a bare rescue swallowing errors. The behavior is unrelated to the package's stated purpose (a request throttling library) and runs automatically as part of the gem's native extension build phase.