Which versions of btc-fee-estimator are malicious?

The following RubyGems versions of btc-fee-estimator are flagged malicious: 0.9.1. Treat any of these as compromised.

How do I remediate btc-fee-estimator if I installed it?

btc-fee-estimator is built to steal secrets, so assume every credential the build or runtime could read is compromised. Remove it from your project and lockfile, then rotate ALL exposed secrets — npm/registry tokens, cloud keys, CI/CD secrets, SSH keys, and any .env values — from a known-clean machine. Audit logs for unauthorized use of those credentials.

I already installed btc-fee-estimator — how do I know if it already compromised me?

If btc-fee-estimator was installed, its post-install payload may already have run. Removing the package does not undo that — check outbound connections and credential use from the install window onward.

Is btc-fee-estimator part of a known attack campaign?

Yes — btc-fee-estimator is associated with the IN-MAL-2026-021353 campaign. Packages in the same campaign often share infrastructure and payloads, so check whether any related packages are also in your dependency tree.

How do I find btc-fee-estimator across my projects, lockfiles, and CI pipelines?

Search your lockfiles and build artifacts for btc-fee-estimator (version 0.9.1).

Malicious package

btc-fee-estimatorRubyGems

Advisory published Oct 11, 2026Updated Oct 11, 2026

btc-fee-estimator is a confirmed malicious RubyGems package (MAL-2026-17781) that steals credentials and exfiltrates sensitive data (malicious version 0.9.1). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in btc-fee-estimator (RubyGems)

MAL-2026-17781

Immediate action

Remove the package, then rotate any secrets the build/runtime could reach.

gem uninstall btc-fee-estimator

What this malware does

The gem's extconf.rb decodes a base64-encoded Ruby payload and evals it inside a detached forked process during gem install. The decoded payload opens a TCP connection to the hardcoded host 45.138.12.177 on port 8089 and bridges it to /bin/sh, providing interactive shell access on the installer's machine. Execution is gated by anti-analysis checks that skip CI environments, hostnames matching firecracker/sandbox/vagrant patterns, generated usernames, analysis paths such as /opt/rubygems and /tmp, machines with uptime under 1800 seconds, and hosts lacking developer artifacts (~/.ssh, ~/.gitconfig, ~/.gem/credentials, ~/.bundle) — targeting real developer workstations while remaining dormant in scanners. The gemspec and README describe unrelated functionality (a bitcoin fee estimator / bitcoin_rpc_lite helpers), and the shipped library exposes only stub methods (build_id, healthy?); the package has no legitimate functionality, serving solely as a cover for the install-time backdoor.

Malicious versions

1 flagged

0.9.1

Indicators of compromise (SHA-256)

ad1e7bee3158f729d88fdaf6a35ebfd32dcdab26ee9de3d8362d1973774b4b7c

Detection & response playbook

Credential / info stealer

Find it
Search your lockfiles and build artifacts for btc-fee-estimator (version 0.9.1).
If you installed it — respond
btc-fee-estimator is built to steal secrets, so assume every credential the build or runtime could read is compromised. Remove it from your project and lockfile, then rotate ALL exposed secrets — npm/registry tokens, cloud keys, CI/CD secrets, SSH keys, and any .env values — from a known-clean machine. Audit logs for unauthorized use of those credentials.
Did it already run?
If btc-fee-estimator was installed, its post-install payload may already have run. Removing the package does not undo that — check outbound connections and credential use from the install window onward.

Frequently asked questions

No. btc-fee-estimator on RubyGems has been identified as a malicious package (version 0.9.1 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

Campaign

IN-MAL-2026-021353

References

rubygems.org

Credits

Amazon Inspector · finder

Detect & block this

O3 blocks btc-fee-estimator-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.

Malware detection Runtime egress monitoring

Explore

All malware advisories How O3 detects malware Vulnerability database