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Vulnerabilities

Vulnerability · CVE-2026-117601

electrum electrum Improper Verification of Cryptographic Signature

Published Oct 27, 2026 · catalog updated Oct 28, 2026 · Electrum

Last checked Nov 6, 2026. A connected source was read within the last 7 days.

Patch now

CVE-2026-117601 is in the CISA known-exploited catalog. Confirm Electrum against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Severity
High7.5
Known exploitation
CISA KEV and VulnCheck KEV
EPSS
0.18%
Remediation
Remediation guidance
Affected products
PyPI electrum · pip electrum · pypi electrum · vendor spesmilo Electrum

### Summary The main Electrum server the client connects to is trusted with mempool ("unconfirmed") transactions. This is documented [design](https://electrum.readthedocs.io/en/latest/faq.html#does-electrum-trust-servers). [0] However now someone figured out a way to practically exploit it: - when the client broadcasts a new tx1, a malicious server can swallow it, - and update the client's history with a conflicting (invalid) tx2 that replaces the outputs with the attacker's output address. - Tx2 has invalid signatures, but this is not checked (due to light client design). - The wallet will display tx2 as an unconfirmed transaction - tx1 will not be displayed. - If the client then manually RBF fee-bumps tx2, the client will sign it with a higher fee, and hence pay the attacker. ### Fixes Commit 90fe30822 contains the fix [1], included in version 4.8.3. The client now verifies the signatures of inputs for mempool txs (before adding them to its local history). Users should upgrade (and regularly do so in any case). As a workaround, without upgrading, when signing any transaction, for bumping the fee or not, they should verify the output addresses and amounts are as expected. Clients that connect to servers they trust (e.g. run their own) are not affected. ### Remarks - some servers are performing this attack in the wild - electrum received two user-reports of this. user1 noticed after broadcasting tx1 the wallet history contained a different tx. user2 bumped the fee of tx2 and lost money. - user1 reported tx1 was not propagated over the bitcoin p2p, so the server held it - both reported the attacker's output address in tx2 was grinded to match the last four chars of the legit address from tx1 - based on user2's report, the server constructed a tx2 with zero fee (presumably in hope of the user bumping its fee) - even with the fix, we still only validate "is_mine" inputs (i.e. paying from addresses that the wallet owns). So e.g. "incoming" txs are not validated. The cli

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

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  • PyPI electrum0 → 4.8.3
  • pip electrum< 4.8.3
  • pypi electrumversion unspecified
  • vendor spesmilo Electrumversion unspecified

How to fix CVE-2026-117601

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

CVE-2026-117601 is in the CISA known-exploited catalog. Confirm Electrum against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Which versions are affected?

Compare what you have installed with 0 → 4.8.3, < 4.8.3. Apply remediations or mitigations per vendor instructions or discontinue use of the product if remediation or mitigations are unavailable.

What should an analyst verify?

CWE-347: Improper Verification of Cryptographic Signature. EPSS 0.18%. The CISA KEV listing is the exploitation evidence. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 27, 2026 · VulnCheck KEV

    Detected

    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.

  2. Oct 27, 2026 · CISA KEV

    Known exploited

    Apply remediations or mitigations per vendor instructions or discontinue use of the product if remediation or mitigations are unavailable.

  3. Oct 28, 2026 · GitHub Advisory Database

    Fix available

    electrum fixed in 4.8.3

  4. Oct 28, 2026 · GitHub Advisory Database

    Fix available

    electrum fixed in 4.8.3

  5. Oct 28, 2026 · GitHub Advisory Database

    Updated

    ### Summary The main Electrum server the client connects to is trusted with mempool ("unconfirmed") transactions. This is documented [design](https://electrum.readthedocs.io/en/latest/faq.html#does-electrum-trust-servers). [0] However now someone figured out a way to practically exploit it: - when the client broadcasts a new tx1, a malicious server can swallow it, - and update the client's history

Sources

  • CVE.orgVulnerability recordCVE-2026-117601

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-117601

    30-day exploitation probability 0.18%

    first.org
  • GitHub Advisory DatabasePackage advisoryGHSA-6jp4-8v48-cc5v

    Electrum: Malicious server can replace a just-broadcast tx and try to trick user into RBF-ing it

    github.com
  • GitLab Advisory DatabasePackage advisoryCVE-2026-117601

    The main Electrum server the client connects to is trusted with mempool ("unconfirmed") transactions. This is documented design. [0] However now someone figured out a way to practically exploit it: when the client broadcasts a new tx1, a malicious server can swallow it, and update the client's history with a conflicting (invalid) tx2 that replaces the outputs with the attacker's output address. Tx

    advisories.gitlab.com
  • OpenSSF OSV / OSV ScannerPackage advisoryGHSA-6jp4-8v48-cc5v

    Electrum: Malicious server can replace a just-broadcast tx and try to trick user into RBF-ing it

    osv.dev
  • VulnCheck KEVConfirmed exploitationCVE-2026-117601

    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 cop

    vulncheck.com

References

Freshness

Last verified in this catalog Nov 6, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSNov 6, 2026
  • VulnCheck KEVOct 31, 2026
  • GitLab Advisory DatabaseOct 30, 2026
  • GitHub Advisory DatabaseOct 30, 2026
  • OpenSSF OSV / OSV ScannerOct 29, 2026
  • CVE.orgOct 28, 2026