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Reproduced Exploit

Autonomint: a lossy CDS withdrawal corrupts totalCdsDepositedAmount

Nov 2024•Other•untagged•2 min read

Chain

Other

Category

untagged

Date

Nov 2024

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: 738. Standalone Foundry PoC and full write-up: 45465-h-12-total-cds-deposited-amount-is-incorrectly-modified-when_exp in the evm-hack-registry mirror.

Vulnerability classes: reward-accounting · locked-funds · integer-bounds

Reproduction: deploys the REAL audited Autonomint protocol (full Core_logic + lib at Sherlock snapshot 0d324e04d4c0ca306e1ae4d4c65f0cb9d681751b) with minimal real doubles only for the opaque external venues (Ionic, WETH, Synthetix, RedStone oracle) and the repo's own EndpointV2Mock LayerZero stack. No mainnet fork.

Root cause#

Before calling the library, CDS.withdraw overwrites cdsDepositDetails.depositedAmount with the loss-adjusted return value. CDSLib.withdrawUserWhoNotOptedForLiq then decrements the aggregate by that already-reduced amount:

SOLIDITY
// lib/CDSLib.sol  (withdrawUserWhoNotOptedForLiq)
totalCdsDepositedAmount -= params.cdsDepositDetails.depositedAmount;      // loss-adjusted!
params.omniChainData.totalCdsDepositedAmount -= params.cdsDepositDetails.depositedAmount;

Removing a 4,000 position that returned only 3,962 leaves the aggregate too high; all subsequent cumulative-value math is computed on the wrong total, stranding USDa.

Vulnerable sources: src/lib/CDSLib.sol (withdrawUserWhoNotOptedForLiq) and src/Core_logic/CDS.sol (withdraw).

Exploit walkthrough (real numbers)#

  1. CDS depositor #1 deposits 4,000 USDT; depositor #2 deposits 6,000 USDT (aggregate 10,000).
  2. A borrower deposits 3 ETH at $1,000 (creates protocol volume).
  3. Price drops to $900; CDS depositor #1 withdraws at a loss and receives 3,962 USDa.
  4. totalCdsDepositedAmount now reads 6,120 while the only remaining depositor owns just 6,000 — an over-counted / stuck ~120 USDa.

test/…_exp.sol asserts the depositor took a loss (< 4,000e6) and the aggregate exceeds the 6,000e6 the remaining depositor owns.

sequenceDiagram participant C1 as CDS depositor 1 participant C2 as CDS depositor 2 participant B as Borrower participant P as CDS pool C1->>P: deposit 4000 C2->>P: deposit 6000 B->>P: borrow 3 ETH (price 1000 -> 900) C1->>P: withdraw at loss -> gets 3962 Note over P: aggregate = 6120 but only 6000 owned (120 stuck)

Reproduction#

BASH
_shared/run-poc/run_poc.sh 45465-h-12-total-cds-deposited-amount-is-incorrectly-modified-when_exp -vvvvv

Sources & further analysis#

Reproductions & code

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