Threshold: Every Wormhole tBTC redemption reverts because the redeemer's satoshi balance is never cre

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 63508-requestredemption-reverts-because-l1btcredeemerwormholes-ban. The historical source/toolchain is unavailable; this entry is documentation only and claims no executable Forge PoC.

Vulnerability classes: vuln/locked-funds

Reproduction: a faithful minimal reproduction of the vulnerable finding — the vulnerable function is reproduced verbatim (marked @>) with faithful minimal doubles; local deploy, no fork.

Root cause#

Every Wormhole tBTC redemption reverts because the redeemer's satoshi balance is never credited in the Bank, so Bridge.requestRedemption's bank.transferBalanceFrom reverts ("Transfer amount exceeds balance") — bridged tBTC is permanently stranded (redemption-path DoS).

    ) internal returns (uint256 redemptionKey, uint256 tbtcAmount) {
        // This contract (as balanceOwner) approves the Bridge to spend its Bank balance.
        // The amount for Bank allowance is in satoshi units (which is what `amount` already is).
        bank.increaseBalanceAllowance(address(thresholdBridge), amount); // @> grants the Bridge an allowance but NEVER credits this contract's Bank balance (the `tbtcVault.unmint` credit is missing) — Bridge.transferBalanceFrom later reverts

        // This contract calls the Bridge. The Bridge will see `msg.sender` (this contract) as the `balanceOwner`.

Why it's exploitable here#

Every Wormhole tBTC redemption reverts because the redeemer's satoshi balance is never credited in the Bank, so Bridge.requestRedemption's bank.transferBalanceFrom reverts ("Transfer amount exceeds balance") — bridged tBTC is permanently stranded (redemption-path DoS).

Attack path#

Marked-line walkthrough (Playground)#

The EVM Playground pins each step to the exact executed source line in 0xcc0e8eedd7…:

1. L371 — Complete Wormhole transfer payload: Setup: completeTransferWithPayload finalizes the inbound Wormhole tBTC transfer and returns the encoded redemption payload.
2. L389 — Redemption amount in satoshis: Setup: supplies amountInSatoshis, the bridged tBTC amount in satoshi units that the redemption is meant to move.
3. L397 — Declare main UTXO argument: Setup: declares the mainUtxo parameter the wallet uses to fund this Bitcoin redemption request.
4. L403 — Grants allowance, never credits balance: Root cause: only calls increaseBalanceAllowance for the bridge but never credits the redeemer's Bank satoshi balance, leaving it at zero.
5. L406 — Call requestRedemption on bridge: Invokes requestRedemption, whose internal transferBalanceFrom reverts 'Transfer amount exceeds balance' because the balance was never credited.
6. L418 — Read back redemption request: Would fetch the stored RedemptionRequest, but this line is never reached since requestRedemption already reverted.
7. L428 — Redemption amount field: Setup: redemptionAmountSat is the request struct's satoshi amount, part of the record the reverting call never gets to create.

PoC#

Registry (Foundry, local deploy — verbatim vulnerable source + harm-asserting test + negative control):

cd 63508-requestredemption-reverts-because-l1btcredeemerwormholes-ban_exp
forge test -vvv

The browser Playground replays the same synthetic opcode-for-opcode and measures the harm: Every Wormhole tBTC redemption reverts because the redeemer's satoshi balance is never credited in the Bank, so Bridge.requestRedemption's b. Both gates are green (registry forge test PASS + Playground _verify-poc VERDICT: PASS).

Sources & further analysis#

Reproductions & code

• No executable Forge reproduction is claimed; the historical source/toolchain was unavailable for this finding.
• AuditVault finding: 63508-requestredemption-reverts-because-l1btcredeemerwormholes-ban.
• Upstream DeFiHackLabs PoC directory: src/test.

Alerts & third-party analyses

• DeFiHackLabs incident explorer: search "Threshold: Every Wormhole tBTC redemption reverts because the redeemer's satoshi balance is never cre".
• Web3Sec X hacked database: search.
• Rekt leaderboard: search.
• Solodit incident search: search.

These dashboards index community alerts tweets, post-mortems, and independent write-ups. Reach them through the protocol name above to cross-check this reproduction against other analyses.