MAL-2026-17568 Malicious code in req-throttle-mini (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 8089. 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 script extconf.rb base64-decodes an embedded Ruby payload, writes it to a randomized file under the system temp directory, and spawns a detached ruby process on it before invoking mkmf's create_makefile. The decoded payload opens a TCP connection to the hardcoded bare IP 45.138.12.177 on port 8089 and bridges the socket bidirectionally to /bin/sh, giving the remote endpoint interactive command execution on the installing host. The payload loops with a 30-second sleep to re-dial on disconnect, providing persistent reconnection. The C2 destination is concealed as a base64 literal rather than appearing in plaintext, and the behavior is unrelated to any native build step.