vulnerability / NVI-00009040 / Revision 2
Electrum: Malicious server can replace a just-broadcast tx and try to trick user into RBF-ing it
GitHub lists this reviewed advisory for electrum. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
7.5 critical
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
0.176%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.07132. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
electrum
source listed< 4.8.3
### Summary 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. - 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 `wallet.is_mine` 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
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-6jp4-8v48-cc5v ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-117601 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.