Primev — Overpayment to bidder in `slash` due to incorrect amount transfer

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 46246-overpayment-to-bidder-in-slash-function-due-to-incorrect-amo. Standalone Foundry PoC and full write-up: 46246-overpayment-to-bidder-in-slash-function-due-to-incorrect-amo_exp in the evm-hack-registry mirror.

Vulnerability classes: vuln/logic/wrong-transfer-amount · vuln/accounting/fee · vuln/logic/direct-drain

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/46246-overpayment-to-bidder-in-slash-function-due-to-incorrect-amo_exp.sol.

AuditVault taxonomy: lang/solidity · platform/cantina · has/poc · severity/high · sector/staking · genome: wrong-condition · direct-drain · account-signer · fee-accounting · reward-accounting

Key info#


Impact	HIGH — slash pays full `amt` to the bidder while only debiting `residualAmt + fee` from provider stake; excess drains registry ETH
Protocol	Primev — `ProviderRegistry.slash`
Vulnerable code	`bidder.call{value: amt}` should be `residualAmt`
Bug class	Wrong transfer amount after correct residual computation
Finding	Cantina — Primev · #46246 · reporter Nexarion
Report	Cantina Primev PDF
Source	AuditVault
Status	Audit finding. Reproduced here as a standalone local PoC.
Compiler	`^0.8.24` (PoC)

TL;DR#

slash computes residualAmt = amt * residualBidPercentAfterDecay / 100%.
Provider stake is reduced by residualAmt + fee (correct).
Bidder is paid amt instead of residualAmt.
With 50% decay, bidder gets 1 ETH instead of 0.5 ETH — 0.5 ETH excess from the registry.

The vulnerable code#

SOLIDITY

uint256 residualAmt = (amt * residualBidPercentAfterDecay) / ONE_HUNDRED_PERCENT;
// ... debit residualAmt + fee from providerStake ...
(bool ok, ) = bidder.call{value: amt}(""); // @> VULN: should be residualAmt

Fix: transfer residualAmt to the bidder.

Root cause#

Residual/decay accounting is applied to the provider debit but not to the bidder credit — asymmetric transfer.

Preconditions#

Provider has stake ≥ slash amount.
Caller is authorized preconf manager.
residualBidPercentAfterDecay < 100%.

Attack walkthrough#

Provider stakes 2 ETH.
Slash 1 ETH with 50% residual → residualAmt = 0.5 ETH.
Bidder receives 1 ETH; provider loses only residual+fee.
Registry ETH short by the excess payment.

Diagrams#

flowchart TD A["slash amt=1 ETH residual%=50"] --> B["residualAmt = 0.5 ETH"] B --> C["providerStake -= residualAmt + fee"] B --> D{"bidder payment"} D -->|"BUG"| E["send amt = 1 ETH"] D -->|"FIX"| F["send residualAmt = 0.5 ETH"] E --> G["registry overpays 0.5 ETH"]

Impact#

Repeated slashes with decay drain the registry's ETH balance (other providers' stakes / protocol float).

Sources#

AuditVault finding #46246
Cantina Primev report
Reduced source: Primev ProviderRegistry.slash (Cantina competition codebase)

Sources & further analysis#

Reproductions & code

Standalone PoC + full trace: 46246-overpayment-to-bidder-in-slash-function-due-to-incorrect-amo_exp (evm-hack-registry mirror).
AuditVault finding: 46246-overpayment-to-bidder-in-slash-function-due-to-incorrect-amo.

Alerts & third-party analyses

Web3Sec X hacked database: search.
Rekt leaderboard: search.
Solodit incident search: search.

These dashboards index community alerts tweets, post-mortems, and independent write-ups. Reach them through the protocol name above to cross-check this reproduction against other analyses.

Source-level debugger — step opcodes and Solidity in sync