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Reproduced Exploit

Decent — Failed `execute` refunds a phantom source-adapter address

1. Source DecentBridgeAdapter calls the router; _getCallParams packs msg.sender (the adapter) as from. 2. Destination onOFTReceived → executor.execute(_from, _to, ...). 3. If the target call fails, _executeWeth does weth.transfer(from, amount). 4. Adapters are not CREATE2-aligned across chains → fr…

Jan 2024•Other•untagged•4 min read

Chain

Other

Category

untagged

Date

Jan 2024

Source

AuditVault

PoC & write-upPoC for your local evm-hack-analyzerAuditVault PoCs

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Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 30561-h-03-when-decentbridgeexecutorexecute-fails-funds-will-be-se. Standalone Foundry PoC and full write-up: 30561-h-03-when-decentbridgeexecutorexecute-fails-funds-will-be-se_exp in the evm-hack-registry mirror.

Vulnerability classes: vuln/wrong-condition · impact/loss-of-funds/direct-drain · genome/bridge-message-validation

Reproduction: a self-contained Foundry PoC that compiles & runs in an isolated project with only forge-std — no fork, no RPC, no anvil_state. Full trace: output.txt. PoC: test/30561-h-03-when-decentbridgeexecutorexecute-fails-funds-will-be-se_exp.sol.

AuditVault taxonomy: lang/solidity · platform/code4rena · has/github · has/poc · severity/high · sector/bridge · genome: wrong-condition · direct-drain · bridge-message-validation

Key info#

ImpactHIGH — when the destination target call fails, the full bridged amount is refunded to the source-chain adapter address (not the user), which is not a contract on the destination → permanent fund loss
ProtocolDecent — DecentEthRouter + DecentBridgeExecutor
Vulnerable code_getCallParams encodes msg.sender as from; _executeWeth/_executeEth refund from on failure
Bug classWrong refund recipient in cross-chain failure path
FindingCode4rena — Decent, 2024-01 · #30561 (H-03) · reporter ZdravkoHr
Report2024-01-decent
SourceAuditVault
StatusAudit finding — confirmed by Decent. Local synthetic reproduces the misdirected refund.
Compiler^0.8.24 (PoC)

TL;DR#

  1. Source DecentBridgeAdapter calls the router; _getCallParams packs msg.sender (the adapter) as from.
  2. Destination onOFTReceived → executor.execute(_from, _to, ...).
  3. If the target call fails, _executeWeth does weth.transfer(from, amount).
  4. Adapters are not CREATE2-aligned across chains → from is a phantom address on dest.
  5. HARM in the PoC: 10 WETH refunded to the source-adapter address; user gets nothing.

The vulnerable code#

SOLIDITY
// _getCallParams (source)
payload = abi.encode(
    msgType,
    msg.sender, // @> VULN: source adapter as refund `from`
    _toAddress,
    deliverEth,
    additionalPayload
);

// _executeWeth (destination) on failure
if (!success) {
    weth.transfer(from, amount); // @> VULN: refunds wrong chain's address
    return;
}

Fix: pass / refund the real user (e.g. destination recipient or an explicit refund address), never the source adapter.

Root cause#

The payload's from was intended as "original user" but is actually the immediate msg.sender on the source (the adapter). The failure refund path trusts that field without translating it to a destination-valid user address. Non-CREATE2 deployments make same-address recovery impossible.

Preconditions#

  • Cross-chain transfer with payload (UTB / adapter path) so from is the adapter.
  • Destination target call fails (revert / OOG / bad calldata).
  • Adapter addresses differ across chains (true for audited deploy scripts).

Attack walkthrough#

  1. Source adapter builds payload → from = sourceAdapter.
  2. Destination credits WETH and calls execute(from, failingTarget, amount, ...).
  3. Target reverts → executor refunds WETH to from.
  4. WETH sits on a phantom address; user cannot recover it.

Diagrams#

flowchart TD A["Source adapter builds payload"] --> B["from = msg.sender = adapter"] B --> C["Dest executor.execute from target amount"] C --> D{"target.call succeeds?"} D -- "no" --> E["weth.transfer from amount"] E --> F["from is phantom on dest"] F --> G["HARM: full amount lost"]
sequenceDiagram participant SA as SourceAdapter participant SR as SourceRouter participant EX as Executor participant T as FailingTarget SA->>SR: buildPayload to=target Note over SR: encode from=SA SR-->>SA: payload Note over EX: dest delivery EX->>T: call payload T-->>EX: revert EX->>SA: weth.transfer SA amount Note over SA: phantom on dest — funds stuck

Remediation#

DIFF
- executor.execute(_from, _to, deliverEth, _amount, callPayload);
+ executor.execute(_to /* or explicit user refund */, _to, deliverEth, _amount, callPayload);

And/or stop encoding the adapter as from in _getCallParams.

How to reproduce#

BASH
cd ~/RustroverProjects/audits/evm-hack-registry/30561-h-03-when-decentbridgeexecutorexecute-fails-funds-will-be-se_exp
forge test -vvv

Sources#

Sources & further analysis#

Reproductions & code

Alerts & third-party analyses

  • Web3Sec X hacked database: search.
  • Rekt leaderboard: search.
  • Solodit incident search: search.

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