---
id: "CVE-2026-117601"
kind: "vulnerability"
aliases: ["CVE-2026-117601"]
title: "Electrum: unverified mempool signatures let malicious servers swap transactions"
severity: "critical"
cvss: 9.3
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["bitcoin", "desktop", "electrum", "package", "wallets"]
not_affected_if: ["electrum-4.8.3-or-later", "trusted-own-server"]
published_at: "2026-10-27T14:16:39+00:00"
first_seen_at: "2026-10-27T14:32:19+00:00"
updated_at: "2026-10-27T14:32:44+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-117601", "first_seen_at": "2026-10-27T14:32:19+00:00"}]
---

# Electrum: unverified mempool signatures let malicious servers swap transactions

Electrum before 4.8.3 does not verify signatures on wallet-owned inputs of unconfirmed mempool transactions. A malicious Electrum server can replace a just-broadcast transaction with a conflicting zero-fee copy that pays an attacker address, and the wallet can show it as valid.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `electrum version` and confirm the installed version is below `4.8.3`
- Check the Electrum version in each wallet installation, including mobile and hardware-wallet hosts that run Electrum

## Fix

- Upgrade Electrum to `4.8.3` or later
- Until upgraded, avoid connecting to untrusted or unknown Electrum servers and check transaction details before fee-bumping or signing

## Timeline

- 2026-10-27T14:32:19+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-117601

## From the sources

Electrum before 4.8.3 fails to verify signatures of wallet-owned inputs in unconfirmed mempool transactions, allowing malicious servers to replace a just-broadcast transaction with a conflicting one. Attackers can swallow the user's transaction and display an invalid zero-fee copy paying an attacker address, tricking users into RBF fee-bumping and signing it.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_