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Reproduced Exploit

Ammplify — H-11: Segment-split geometric-mean borrow overstates taker fees

1. Full-range borrow at one GM tick is the economically intended base. 2. Segment tree stores liq in multiple nodes; each uses its own GM. 3. Sum of segment borrows ≫ full-range borrow (convexity of amounts vs tick). 4. Fee = rate × inflated base → takers overcharged.

Sep 2025•Other•untagged•2 min read

Chain

Other

Category

untagged

Date

Sep 2025

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: 63177-h-11-takers-pay-significantly-higher-fees-than-expected-due. Standalone Foundry PoC and full write-up: 63177-h-11-takers-pay-significantly-higher-fees-than-expected-due_exp in the evm-hack-registry mirror.

Vulnerability classes: fee-calculation · wrong-state

Reproduction: self-contained Foundry PoC with only forge-std. Full trace: output.txt.

AuditVault taxonomy: severity/high · sector/dex · platform/sherlock · fee-calculation · wrong-state

Key info#

ImpactHIGH — takers overpay fees (segment sum ≫ full-range borrow)
ProtocolAmmplify
Vulnerable codecomputeBorrows uses per-segment geometric mean; tree split inflates sum
Finding#63177 / issue 452 · panprog
Compiler^0.8.24

TL;DR#

  1. Full-range borrow at one GM tick is the economically intended base.
  2. Segment tree stores liq in multiple nodes; each uses its own GM.
  3. Sum of segment borrows ≫ full-range borrow (convexity of amounts vs tick).
  4. Fee = rate × inflated base → takers overcharged.

The vulnerable code#

SOLIDITY
int24 gmTick = lowTick + (highTick - lowTick) / 2; // @> VULN: per-segment GM
// FIX: compute full-range borrows once, split by width

Diagrams#

flowchart TD A["Taker range spanning many nodes"] --> B["Each node computeBorrows at own GM"] B --> C["Sum segment borrows"] D["Full-range GM borrow"] --> E["Expected base"] C --> F["Inflated base"] E --> G["Fee expected"] F --> H["Fee charged much higher"]

Sources#

Sources & further analysis#

Reproductions & code

Alerts & third-party analyses

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