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Reproduced Exploit

Open Dollar — incorrect calculations for surplus auction creation

1. auctionSurplus compares surplusTransferPercentage to ONE_HUNDRED_WAD (always true). 2. amountToSell uses wmul(ONE_HUNDRED_WAD - pct) → ~99× surplusAmount. 3. At 100% transfer, a ghost auction of 297 still starts while 3 is transferred. 4. Double-counting breaks accounting and can underflow elsew…

Oct 2023•Other•untagged•2 min read

Chain

Other

Category

untagged

Date

Oct 2023

Source

AuditVault

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

EVM Playground

Source-level debugger — step opcodes and Solidity in sync

evm-hack-analyzer

The attack is replayed in an in-browser EVM preloaded with the exact dumped fork state. The execution tree shows every call; step by Solidity line or by opcode across all depths — source, Stack, Memory, Storage, Balances (native / ERC-20 / NFT), Transient storage and Return value stay in sync. Click a tree node, opcode, or source line to jump. No backend, no live RPC.

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Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 29347-h-01-incorrect-calculations-for-surplus-auction-creation-cau. Standalone Foundry PoC and full write-up: 29347-h-01-incorrect-calculations-for-surplus-auction-creation-cau_exp in the evm-hack-registry mirror.

Vulnerability classes: underflow · known-pattern · direct-drain · integer-bounds

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/29347-h-01-incorrect-calculations-for-surplus-auction-creation-cau_exp.sol.

Key info#

ImpactHIGH — ONE_HUNDRED_WAD used instead of WAD creates 99× inflated ghost surplus auctions and double-counts surplus
ProtocolOpen Dollar
Vulnerable codeAccountingEngine
Bug classunderflow
FindingCode4rena — Open Dollar, 2023-10 · #29347 · reporter tnquanghuy0512
Reportcode4rena.com/reports/2023-10-opendollar
SourceAuditVault
StatusAudit finding — caught in review, not exploited on-chain. Reproduced as a standalone local PoC.
Compiler^0.8.24 (PoC)

This is an audit finding, not a historical on-chain incident. The PoC keeps the vulnerable logic verbatim (marked @> VULN) and reduces dependencies to the minimum needed to show the claimed harm.

TL;DR#

  1. auctionSurplus compares surplusTransferPercentage to ONE_HUNDRED_WAD (always true).
  2. amountToSell uses wmul(ONE_HUNDRED_WAD - pct) → ~99× surplusAmount.
  3. At 100% transfer, a ghost auction of 297 still starts while 3 is transferred.
  4. Double-counting breaks accounting and can underflow elsewhere.

The vulnerable code#

See test/29347-h-01-incorrect-calculations-for-surplus-auction-creation-cau.sol — the @> VULN marker is on the blamed line (line 130 in the synthetic).

Root cause#

Percentage math uses ONE_HUNDRED_WAD (100e18) where WAD (1e18) is required.

Preconditions#

Protocol operating conditions that make the path reachable (see finding report). No exotic privileges beyond those the real call path requires.

Attack walkthrough#

From output.txt: the Exploit.run() path executes the attack end-to-end and requires the harm.

Diagrams#

flowchart TD A[Setup reduced protocol state] --> B[Trigger vulnerable path] B --> C[VULN line executes] C --> D[Harm asserted]

Impact#

Massively inflated surplus auctions plus full transfer — accounting insolvency risk.

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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