{"id":"CVE-2026-117601","kind":"vulnerability","aliases":["CVE-2026-117601"],"related":[],"title":"Electrum: unverified mempool signatures let malicious servers swap transactions","description":"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.","summary":"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.","severity":"critical","cvss":9.3,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["bitcoin","desktop","electrum","package","wallets"],"not_affected_if":["electrum-4.8.3-or-later","trusted-own-server"],"how_to_check":"- Run `electrum version` and confirm the installed version is below `4.8.3`\n- 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\n- Until upgraded, avoid connecting to untrusted or unknown Electrum servers and check transaction details before fee-bumping or signing","status":"open","published_at":"2026-10-27T14:16:39+00:00","first_seen_at":"2026-10-27T14:32:19+00:00","triaged_at":"2026-10-27T14:32:44+00:00","updated_at":"2026-10-27T14:32:44+00:00","category":"package","confidence":0.6,"triage":{"at":"2026-10-27T14:32:44Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade Electrum to `4.8.3` or later\n- Until upgraded, avoid connecting to untrusted or unknown Electrum servers and check transaction details before fee-bumping or signing","reach":"internet","title":"Electrum: unverified mempool signatures let malicious servers swap transactions","impact":"high","summary":"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.","category":"package","nicknames":[],"who_cares":["electrum","bitcoin","wallets","desktop"],"confidence":0.6,"needs_auth":"no","worst_case":"Attacker swaps user's transaction, redirecting funds to attacker address","analyst_note":"Check the Electrum 4.8.3 release notes and the NVD entry for the exact affected version range and whether any server-side or hardware-wallet specifics apply.","how_to_check":"- Run `electrum version` and confirm the installed version is below `4.8.3`\n- Check the Electrum version in each wallet installation, including mobile and hardware-wallet hosts that run Electrum","needs_analyst":true,"not_affected_if":["electrum-4.8.3-or-later","trusted-own-server"],"who_is_affected":"Any user running Electrum before 4.8.3 who broadcasts transactions through a server they do not fully control. The risk is the server returning a conflicting unconfirmed transaction that the wallet fails to reject. Users who run only trusted self-hosted servers or have already upgraded can skip it.","user_interaction":"yes","needs_special_setup":"unknown","severity_if_unknown":"critical"},"cost_usd":0.000649,"input_tokens":3352,"output_tokens":627,"severity_before":"critical"},"analyst_status":null,"analyst_note":null,"search":"'-117601':12A,15A '-2026':11A,14A '4.8.3':23B,70C 'address':59B,116C 'allow':84C 'attack':58B,98C,115C 'bitcoin':16B 'broadcast':46B,92C 'bump':123C 'conflict':50B,96C 'copi':54B,112C 'cve':10A,13A 'desktop':17B 'display':106C 'electrum':1A,18B,21B,39B,68C 'fail':71C 'fee':53B,111C,122C 'fee-bump':121C 'input':32B,79C 'invalid':108C 'just-broadcast':44B,90C 'let':5A 'malici':6A,38B,85C 'mempool':3A,35B,82C 'one':97C 'own':31B,78C 'packag':19B 'pay':56B,113C 'rbf':120C 'replac':42B,88C 'server':7A,40B,86C 'show':64B 'sign':125C 'signatur':4A,27B,74C 'swallow':100C 'swap':8A 'transact':9A,36B,47B,83C,93C,104C 'trick':117C 'unconfirm':34B,81C 'unverifi':2A 'user':102C,118C 'valid':67B 'verifi':26B,73C 'wallet':20B,30B,62B,77C 'wallet-own':29B,76C 'zero':52B,110C 'zero-fe':51B,109C","nicknames":[],"mitigations":[],"who_affected":"Any user running Electrum before 4.8.3 who broadcasts transactions through a server they do not fully control. The risk is the server returning a conflicting unconfirmed transaction that the wallet fails to reject. Users who run only trusted self-hosted servers or have already upgraded can skip it.","tier":"B","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-27T14:16:39+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","cvss_by":"disclosure@vulncheck.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-117601","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-117601","severity":null,"published_at":"2026-10-27T14:16:39+00:00","modified_at":"2026-10-27T14:16:39+00:00","first_seen_at":"2026-10-27T14:32:19+00:00","fetched_at":"2026-10-27T14:32:19+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}