CVE-2026-56744: `@bsv/wallet-toolbox` / `-client` / `-mobile` don't verify storage-supplied recipient output scripts against caller-requested outputs in createAction (can redirect payments when using remote storage)
@bsv/wallet-toolbox provides BRC-100 wallet signing and storage components, while @bsv/wallet-toolbox-client and @bsv/wallet-toolbox-mobile provide client-focused distributions for standard and mobile applications using wallet storage services. A vulnerability in these packages causes transactions created through a remote StorageClient to trust output locking scripts returned by the storage provider without verifying that they match the outputs requested by the caller. A malicious or compromised storage provider can substitute a recipient script or inject an additional output, causing the wallet to sign and broadcast a transaction that redirects funds while the application and user interface continue to display the intended recipient. Source and npm publication history indicate that stable versions @bsv/wallet-toolbox and @bsv/wallet-toolbox-client from 1.1.47 through 2.3.3, and @bsv/wallet-toolbox-mobile from its initial 1.3.21 release through 2.3.3, are affected. All three packages are patched in version 2.4.0. Applications unable to upgrade should avoid remote StorageClient providers, use local storage, or independently verify every transaction output’s locking script and value against the original request before signing
Other sources
Reported by @echennells (Eric Chennells). Migrated from public issue #191 to a private advisory.
Affected: @bsv/wallet-toolbox / -client / -mobile. Verified in 2.1.21 and 2.1.21-parity-fix.2; the relevant code is the same at current HEAD
Summary: When createAction runs against a remote StorageClient, the storage server returns the outputs to build. buildSignableTransaction takes each non-change output's lockingScript from the storage response and signs it, without comparing it to the lockingScript the caller supplied in args.outputs. WalletPermissionsManager.createAction parses the built transaction and has args.outputs available, but uses the tx only for inputs and getFee(); it does not inspect tx.outputs. A storage provider that returns a different recipient script than requested will therefore have that script signed and broadcast, while the calling app and UI still show the originally requested recipient.
Relevant code: - signer/methods/buildSignableTransaction.js — non-change output lockingScript = asBsvSdkScript(out.lockingScript), sourced from the storage response; args.outputs is not consulted. - WalletPermissionsManager.js createAction — parses the built tx, derives spend from args.outputs satoshis + tx.getFee(), reads tx.inputs; does not read tx.outputs. - signer/methods/signAction.js, completeSignedTransaction.js — sign the as-built tx; no output comparison.
Context: Remote storage is a supported, default configuration (StorageClient over BRC-103 AuthFetch, default endpoint storage.babbage.systems, optional payment middleware). The mutual auth establishes the storage server's identity and protects the channel, but the contents it returns are not validated against the request. The attacker is the storage operator, or anyone who compromises it — not a passive network MITM. (StorageServer.processAction does compare the signed rawTx outputs to what storage stored, so a response-only MITM is rejected; an operator stores the substituted script from the start.)
Proof of concept: We ran a storage server that returns a substituted recipient output, and pointed a current yours-wallet build at it as its active storage provider. With the wallet otherwise unmodified, a payment requested to one address was built, signed, and broadcast paying a different address, the substitution was not surfaced anywhere in the wallet.
— GitHub
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/@bsv/wallet-toolbox-mobileto a version that resolves this vulnerability.Fixed in 2.4.0 - Upgrade
Upgrade
npm/@bsv/wallet-toolbox-clientto a version that resolves this vulnerability.Fixed in 2.4.0 - Upgrade
Upgrade
npm/@bsv/wallet-toolboxto a version that resolves this vulnerability.Fixed in 2.4.0 - Upgrade
Upgrade
@bsv/wallet-toolbox / @bsv/wallet-toolbox-client / @bsv/wallet-toolbox-mobileto a version that resolves this vulnerability.Fixed in 2.4.0 - Compensating control
If unable to upgrade, avoid remote StorageClient providers by using local storage, or independently verify every transaction output's locking script and value against the original request before signing.
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Applications using a remote StorageClient with affected versions are exposed. The affected ranges are @bsv/wallet-toolbox and @bsv/wallet-toolbox-client 1.1.47 through 2.3.3, and @bsv/wallet-toolbox-mobile 1.3.21 through 2.3.3.
What must an attacker control to redirect a payment?
The attacker must operate or compromise the remote storage provider used by the application. That provider can return altered output locking scripts or add an output during createAction, leading the wallet to sign and broadcast a transaction different from the one shown to the user.
Are local-storage deployments affected?
The described issue occurs when transactions are created through a remote StorageClient that supplies transaction outputs. Using local storage avoids relying on a remote provider for those output scripts.
What can be done if upgrading is not immediately possible?
Avoid remote StorageClient providers and use local storage where possible. If remote storage must be used, independently verify every transaction output's locking script against the outputs requested by the caller before signing or broadcasting.
How can this be remediated?
Upgrade all affected package variants to version 2.4.0, which is patched. Review applications that use remote storage providers, particularly any flow that creates and signs payments through createAction.