block-explorer-api

Details

**Severity:** Critical

**Affected versions:** `= 0.9.1`

## Source: amazon-inspector (9cfaa3470065369addbb91e3a6c2072e8add334c4d27bff95f91315aa58ae313)
The gem's native-extension build script (extconf.rb) decodes a base64-encoded Ruby payload and passes it to eval() inside a double-forked, detached child process with stdio redirected to /dev/null. The decoded payload opens a TCP connection to the hardcoded bare-IP C2 45.138.12.177:8089 and bridges it to /bin/sh via IO.popen and IO.copy_stream in both directions, yielding a full interactive reverse shell on the installer's host under the installing user. Execution is gated by anti-analysis checks that skip CI runners, ephemeral/sandbox hostnames (uvm, firecracker, sandbox, vagrant), generated analyst usernames (uA\d+, sandbox, tester, analys, scanner), common analysis working paths (/opt/rubygems, /tmp, /var/tmp, /workspace), and hosts with uptime under 1800 seconds, firing only when developer-signal files such as ~/.ssh, ~/.gem/credentials, ~/.gitconfig, or ~/.npmrc are present, and after a randomized 20-40 minute delay. The shipped library at lib/block_explorer_api.rb is an inert 10-line stub (VERSION, build_id, healthy?) and the gemspec name (block-explorer-api, authored by generic 'block maintainers') does not match the README, which describes the package as 'bitcoin-rpc-lite'; the install hook contains the entire functional payload while the advertised library does nothing.

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Credit: [OpenSSF](https://github.com/ossf/malicious-packages) ([source](https://github.com/ossf/malicious-packages/blob/ff41f6680a0ebbef2268cdb5daf253d4b400cb05/osv/malicious/rubygems/block-explorer-api/MAL-2026-17780.json))

**References:**
- https://github.com/ossf/malicious-packages/blob/ff41f6680a0ebbef2268cdb5daf253d4b400cb05/osv/malicious/rubygems/block-explorer-api/MAL-2026-17780.json
- https://rubygems.org/gems/block-explorer-api/versions/0.9.1
- https://github.com/advisories/GHSA-hg3j-6p9h-76jm

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.