# \[Security Disclosure\] SDM Verify Path Accepts Forged Refunds Without Recomputation — Pre-Lagoon Critical

**URL:** <https://gov.optimism.io/t/security-disclosure-sdm-verify-path-accepts-forged-refunds-without-recomputation-pre-lagoon-critical/10774>\
**Category:** Governance Design and Strategy  📐\
**Created:** [July 21, 2026, 8:46pm UTC](https://gov.optimism.io/t/security-disclosure-sdm-verify-path-accepts-forged-refunds-without-recomputation-pre-lagoon-critical/10774 "2026-07-21T20:46:56Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![YomibitoShirazu](https://dub1.discourse-cdn.com/bc41dd/user_avatar/gov.optimism.io/yomibitoshirazu/32/13084_2.png) [@YomibitoShirazu](https://gov.optimism.io/u/YomibitoShirazu)\
**Post date:** [July 21, 2026, 8:46pm UTC](https://gov.optimism.io/t/security-disclosure-sdm-verify-path-accepts-forged-refunds-without-recomputation-pre-lagoon-critical/10774/1 "2026-07-21T20:46:56Z")

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## 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

1. Confirm whether the recomputation check will be added to  
verifier\_post\_exec\_refund\_for\_tx before Lagoon activates
2. Reopen Immunefi Report #83996 and evaluate under the June  
2025 bounty extension covering pre-production upgrades

## References

Full disclosure:

> **[YomibitoShirazu | Protocol Security](https://paragraph.com/@yomibitoshirazu)**

PoC repository:

> **[GitHub - Yomibito-Shirazu-jp/The-Collapse-of-Optimism-PoC](https://github.com/Yomibito-Shirazu-jp/The-Collapse-of-Optimism-PoC)**
>
> Contribute to Yomibito-Shirazu-jp/The-Collapse-of-Optimism-PoC development by creating an account on GitHub.

— Yomibito Shirazu / Yohei Ishijima

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<div class="post-metadata">

**Author:** ![ben-chain](https://avatars.discourse-cdn.com/v4/letter/b/b5a626/32.png) [@ben-chain](https://gov.optimism.io/u/ben-chain)\
**Post date:** [August 11, 2026, 4:40pm UTC](https://gov.optimism.io/t/security-disclosure-sdm-verify-path-accepts-forged-refunds-without-recomputation-pre-lagoon-critical/10774/2 "2026-08-11T16:40:15Z")

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Unlisted on August 11, 2026, 4:40pm UTC