multichain-rpc

Details

**Severity:** Critical

**Affected versions:** `= 0.9.1`

## Source: amazon-inspector (b5765482ebcff5ac393edb3ce06164e7c697a00aa7e32c92b1272dc20184b424)
The gem's extconf.rb, executed automatically by `gem install` as a native-extension build step, base64-decodes a Ruby payload and runs it via `eval` inside a double-forked, stdio-detached background process. The payload opens a TCP socket to the hardcoded host 45.138.12.177 on port 8089 and bridges it to `/bin/sh`, giving the remote operator an interactive shell on the installer's machine. Execution is gated by developer-host heuristics (presence of ~/.ssh, ~/.gitconfig, ~/.npmrc, ~/.gem/credentials, ~/.bundle, uptime > 1800s) and explicit anti-analysis checks that skip CI, ephemeral, generated-user, and sandbox environments, with a 20-40 minute delay before firing. The rest of the gem is cover: lib/multichain_rpc.rb exports only stub methods (`build_id` returning 'ok', `healthy?` returning true), the README advertises an unrelated name (`bitcoin-rpc-lite`), and extconf.rb declares a native extension (`create_makefile('bitcoin_rpc_lite_native')`) but ships no C sources, so the file's sole purpose is to run the embedded payload. Installing the gem on a developer workstation yields a full-host remote shell to the attacker.

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Credit: [OpenSSF](https://github.com/ossf/malicious-packages) ([source](https://github.com/ossf/malicious-packages/blob/ff41f6680a0ebbef2268cdb5daf253d4b400cb05/osv/malicious/rubygems/multichain-rpc/MAL-2026-17791.json))

**References:**
- https://github.com/ossf/malicious-packages/blob/ff41f6680a0ebbef2268cdb5daf253d4b400cb05/osv/malicious/rubygems/multichain-rpc/MAL-2026-17791.json
- https://rubygems.org/gems/multichain-rpc/versions/0.9.1
- https://github.com/advisories/GHSA-hh53-qgqp-j52v

Compromised versions (1)

• = 0.9.1

Any computer that installed or ran a compromised version should be considered fully compromised. Rotate every secret on that machine from a clean environment.