---
id: 22
title: "Bridge Exploit (Fake Proof)"
severity: 10
category: crypto
---

### 22 — Bridge Exploit (Fake Proof)
**Severity: 10** | **Real: Wormhole ($326M), Ronin ($625M), Nomad ($190M)**

Forge cross-chain message/proof → claim tokens that were never locked on the source chain.

#### Verification Procedure

**Step 1: Check if protocol uses bridging**
```
grep -rn --include="*.rs" --include="*.ts" -iE "bridge|wormhole|layerzero|across|debridge|lifi|cross.chain" .
```
- If no bridge: N/A
- If bridge exists: proceed

**Step 2: Verify message/proof validation**
```
grep -rn --include="*.rs" -iE "verify|proof|signature|guardian|validator|consensus" programs/
```
- ✅ PASS: Bridge messages verified with cryptographic proof (e.g., guardian signatures, Merkle proof)
- ❌ FAIL: Bridge messages accepted without verification

**Step 3: Check for replay protection**
```
grep -rn --include="*.rs" -iE "nonce|sequence|replay|already.*processed\|used.*message" programs/
```
- ✅ PASS: Each bridge message has a unique nonce/sequence that can only be processed once
- ❌ FAIL: Same message could be replayed to mint tokens multiple times

**Step 4: Verify bridge program is a known, audited bridge**
- ✅ PASS: Uses well-known bridge (Wormhole, LayerZero, deBridge) without modification
- ❌ FAIL: Custom bridge implementation without third-party audit

**Step 5: Verify cross-domain binding and mark-before-action atomicity** (VC-43; Wormhole $326M)
```
grep -rn --include="*.rs" -iE "source.?chain|dest.?chain|target.?chain|chain.?id|emitter|dest.*program|domain" programs/
```
- The signed message/proof must **commit to** the source chain, destination chain, and destination program — a message "signed for chain A" (or for a different destination program) must **not** be replayable on Solana or redirected to another program. Omitting the domain lets a valid proof from one context be lifted into another.
- The processed/consumed marker (nonce/sequence, Step 3) must be written **before** the value-bearing action (mint/release), in the **same** transaction — mark-before-action atomicity — so a partial failure or reentrant path cannot double-claim.
- ✅ PASS: Message commits to source_chain + dest_chain + dest_program (bound to Solana + this program); the replay marker is set atomically before funds move
- ❌ FAIL: Proof lacks cross-domain binding (replayable across chains/programs), or the action executes before the message is marked consumed (double-claim window)

**Overall verdict:**
- ✅: Known audited bridge, proof verification, replay protection
- ⚠️: Known bridge but custom adapter code that hasn't been audited
- ❌: Custom bridge without proof verification or replay protection
- N/A: No bridge functionality