Electrum: Missing signature verification of mempool transactions
Summary
Electrum before 4.8.3 does not verify signatures of wallet-owned inputs in unconfirmed mempool transactions received from its server. A malicious Electrum server can replace a just-broadcast transaction with a conflicting, invalid zero-fee transaction that pays an attacker's address. If the user then fee-bumps and signs the replacement via RBF, the funds go to the attacker.
Affected
- Electrum versions before 4.8.3 (spesmilo Electrum, all platforms)
Fixed in
- Electrum 4.8.3 (fix in commit 90fe308)
Workaround
- Without upgrading, verify output addresses and amounts on the device or wallet screen before signing any transaction, including fee bumps.
- Users who connect only to self-hosted, trusted Electrum servers are not exposed to this server-based attack.
Exploitation
- Electrum's maintainers state that some servers perform this attack in the wild and that two user reports were received, one with financial loss. Sources conflict; OffSeq lists the CVE as not known to be exploited.
- No public proof-of-concept exploit found; the attack only requires operating or compromising a server.
Our recommendation
- Inventory all Electrum clients and versions and upgrade to 4.8.3 from electrum.org, verifying the GPG signature.
- Until upgraded, check addresses and amounts on the wallet or device before signing, especially fee bumps.
- Use self-hosted or trusted Electrum servers for business payments.
- Note that signatures of incoming transactions are still not validated after the upgrade.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- GitHub Security Advisory GHSA-6jp4-8v48-cc5v github.com
- Fix commit 90fe308 github.com
- VulnCheck advisory www.vulncheck.com
- OSV entry GHSA-6jp4-8v48-cc5v osv.dev
- VulDB entry 427212 vuldb.com
- Vulners NVD record CVE-2026-117601 vulners.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 31 Oct 2026, 00:36.
Original description (NVD)
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.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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