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Malicious code in btc-fee-estimator (RubyGems)

What to do

Vendor response not established. Follow the primary source's mitigation guidance and check back for a fix.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • RubyGems btc-fee-estimator

    Affected
    >= 0.9.1, <= 0.9.1
    Fixed in
    no fixed version recorded

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
not scored
EPSS
No dated EPSS signal available.
Source description

As published by the source; long descriptions are shortened.

--- _-= Per source details. Do not edit below this line.=-_

Source: amazon-inspector (ad1e7bee3158f729d88fdaf6a35ebfd32dcdab26ee9de3d8362d1973774b4b7c) 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…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from osv record MAL-2026-17781

Agent brief

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# Patch Next advisory brief: mal-2026-17781

Advisory: Malicious code in btc-fee-estimator (RubyGems)
IDs: mal-2026-17781
Record: https://patchnext.com/advisories/mal-2026-17781 (revision 1, source checked 23 Oct 2026, 22:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems btc-fee-estimator: affected >= 0.9.1, <= 0.9.1

## Suggested inspection (read-only)
- RubyGems btc-fee-estimator: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on btc-fee-estimator.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/MAL-2026-17781 (OSV record MAL-2026-17781 lists affected ranges: RubyGems btc-fee-estimator >=0.9.1 <=0.9.1)

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