MAL-2026-17792 Malicious code in nft-metadata-resolver (RubyGems)

The gem ships a native-extension script at ext/nft_metadata_resolver/extconf.rb that RubyGems auto-executes during gem install. The script carries a base64-encoded Ruby payload, decodes it with Base64.decode64 and runs it via eval inside a double-forked, detached, delayed child process. The decoded payload opens a TCP connection to the hardcoded bare-IP endpoint 45.138.12.177:8089 and bridges /bin/sh standard I/O to that socket using IO.popen and IO.copy_stream in both directions, giving the remote endpoint an interactive shell on the installer's host. Execution is gated by sandbox-evasion checks that skip CI environments, ephemeral or sandbox hostnames, generated analyst-shaped usernames, analysis working directories, and hosts with short uptimes, firing only when developer-shaped home-directory signals are present. The gem's advertised identity is inconsistent with its contents: the package is published as nft-metadata-resolver, the README describes a 'bitcoin-rpc-lite' library, and the extension declares a makefile target named bitcoin_rpc_lite_native while shipping no native C/C++ source for a real addon build. The extconf.rb's sole purpose is to decode and execute the embedded payload.

The OpenSSF Package Analysis project identified 'nft-metadata-resolver' @ 0.9.1 (rubygems) as malicious.

It is considered malicious because:

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