Lumi Finance (Sodium ERC-4337 account) — Signature-Bypass Drain

Source & credit. Exploit reproduction, trace data, and analysis adapted from DeFiHackLabs by SunWeb3Sec — an open registry of reproduced on-chain exploits. Standalone Foundry PoC and full write-up: 2026-07-LumiFinance_exp in the evm-hack-registry mirror. Upstream DeFiHackLabs PoC: src/test/…/LumiFinance_exp.sol.

Vulnerability classes: vuln/auth/signature-validation · vuln/access-control/broken-logic · vuln/input-validation/missing

Reproduction: the PoC compiles & runs offline in an isolated Foundry project at this project folder; full verbose trace in output.txt. The test test/LumiFinance_exp.sol forks Arbitrum One at block 483389833 (the block before attack tx1) and replays the two real attacker transactions in order against the exact pre-attack fork state — no attack logic is reconstructed. Run it offline with _shared/run_poc.sh 2026-07-LumiFinance_exp -vvvvv.

Key info#

TL;DR#

Sodium is Lumi Finance's ERC-4337 v0.6 smart-account wallet, and its owner check is forgeable: it trusts a signer address taken from the attacker-supplied UserOperation signature, then a soft ECDSA failure falls through to an ERC-1271 staticcall into that attacker contract.

Because the attacker sets signer to a contract they control — one that returns the ERC-1271 magic value 0x1626ba7e for any input — the wallet accepts arbitrary UserOps as owner-authorized. The attacker pushed UserOps making ~50 victim Sodium accounts approve() them for max allowance (tx1), then transferFrom-drained every account (tx2), taking LUA, LUAUSD, USDC, USDC.e, USD₮0 and native ETH.

Addresses#

Drained tokens#

Attack transactions#

• tx1 (0x630654fb1c8914405cf81bb02f091b049f19403a152f624f7b8a00c7724c6604, block 483389834, selector 0x363e464b): pushes UserOps through EntryPoint that make every victim Sodium account approve() the attacker contract for max allowance.
• tx2 (0x1cdba4c3f9c925e6d03ce8d07965a7521ee4e7258f6c5eeae8a7998886c2b9f0, block 483390113, selector 0x96e676e5): for each victim reads balanceOf, then transferFrom(victim, attackerContract, balance) for all five tokens, and finally forwards LUA + LUAUSD + ~1.6 ETH to the attacker EOA.

Root cause — ERC-4337 signature bypass#

Sodium is an ERC-4337 v0.6 smart account. Its _validateSignature calls checkValidSodiumSignature(hash, sig). For signature type 0x01 the account reads a 20-byte signer directly from the attacker-supplied signature blob ({0x01}{signer}{signatureBytes}) and passes it to OpenZeppelin:

SignatureChecker.isValidSignatureNow(signer, hash, signatureBytes)

Because signer is attacker-controlled and is not the real owner:

1. ECDSA.tryRecover(hash, signatureBytes) returns (address(0)/wrong, RecoverError) without reverting.
2. SignatureChecker therefore falls back to the ERC-1271 branch: signer.staticcall(abi.encodeWithSelector(0x1626ba7e, hash, signatureBytes)).
3. signer is set to the attacker's own contract, which returns the ERC-1271 magic value 0x1626ba7e → isValidSignatureNow returns true.

For the executeWithSodiumAuthRecover / executeWithSodiumAuthSession methodId branches, _validateSignature then returns 0 (SIG_VALIDATION success) whenever sessionKey == signer — both attacker-set. The check that should have bound the operation to the account owner instead trusts an address embedded in the unauthenticated signature blob, so the attacker validates arbitrary UserOps against every Sodium account and makes each one approve + get drained.

PoC approach#

test/LumiFinance_exp.sol forks Arbitrum at block 483389833, then from the attacker EOA (vm.startPrank(EOA, EOA) to set both msg.sender and tx.origin) calls the already-deployed on-chain attacker contract with the two real calldata blobs in order (tx1 then tx2). No attack logic is reconstructed — the exact on-chain bytes are replayed against the exact pre-attack fork state. The test asserts the attacker EOA's LUA and LUAUSD balances strictly increase and that total measured gains are positive.

Result#

[PASS] testExploit()
  Attacker EOA gain TOK_c3aBC (LUA)   : 44444.415238902046459663
  Attacker EOA gain TOK_1DD6b (LUAUSD): 61512.087280490418178501
  Attacker EOA gain native ETH        : 1.601793718853233682

The remaining USDC / USDC.e / USD₮0 proceeds are drained into the attacker contract (0x5636…) rather than the EOA, matching the real on-chain transaction. Measured EOA profit: 44,444.42 LUA + 61,512.09 LUAUSD + 1.6018 ETH.

Files#

• test/LumiFinance_exp.sol — the replay PoC
• basetest.sol, tokenhelper.sol, interface.sol — harness
• foundry.toml, remappings.txt, lib/forge-std (symlink) — build config
• output.txt — passing forge test output

Sources & further analysis#

Reproductions & code

• Standalone PoC + full trace: 2026-07-LumiFinance_exp (evm-hack-registry mirror).
• Upstream DeFiHackLabs PoC: LumiFinance_exp.sol.
• Attack transaction: view on explorer.

Alerts & third-party analyses

• DeFiHackLabs incident explorer: search "Lumi Finance (Sodium ERC-4337 account)".
• 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.