CVE-2026-56744

`@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

`@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

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.

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.