Summary
I am disclosing a vulnerability in the SDM/PostExec system
(alloy-op-evm) that allows a malicious sequencer to forge gas
refund values accepted by every verifier without recomputation.
The fault-proof system (kona) shares the same blind spot and
cannot dispute the resulting forged state root.
Current status: Not exploitable. Lagoon has not activated
on any production chain.
Risk if unpatched at activation: 17,280 ETH/day damage
ceiling at stress scenario parameters.
The Defect
verifier_post_exec_refund_for_tx applies only a size cap:
if refund > evm_gas_used { return Err(…) }
Ok(refund) // no recomputation
A malicious sequencer sets refund = evm_gas_used for every
transaction. Every verifier accepts it. The forged value writes
to canonical state_root via post_exec_settlement_deltas.
Proof of Concept
Runs on stock code. No modifications required.
cargo test → VERIFY-NO-RECOMPUTE | accepted=21000 legit=0
Disclosure History
- 7 reports submitted to Immunefi
- $400 in submission fees paid
- Triage confirmed: “yes — technically accurate” — then closed
- Finding forwarded to engineering as “informational hardening note”
- Not paid
Request
- Confirm whether the recomputation check will be added to
verifier_post_exec_refund_for_tx before Lagoon activates - Reopen Immunefi Report #83996 and evaluate under the June
2025 bounty extension covering pre-production upgrades
References
Full disclosure:
PoC repository:
— Yomibito Shirazu / Yohei Ishijima