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Reproduced Exploit

Buck Labs: Stale totalExcludedSupply (1

Jan 1970•Other•untagged•3 min read

Chain

Other

Category

untagged

Date

Jan 1970

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.

Loading fork state…

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 64666-totalexcludedsupply-drifts-from-reality-spearbit-none-buck-l. The historical source/toolchain is unavailable; this entry is documentation only and claims no executable Forge PoC.

Vulnerability classes: vuln/locked-funds · vuln/reward-accounting

Reproduction: a faithful minimal reproduction of the vulnerable finding — the vulnerable function is reproduced verbatim (marked @>) with faithful minimal doubles; local deploy, no fork.

Root cause#

Stale totalExcludedSupply (1,000,000e18) exceeds the shrunken totalSupply (100,000e18) after an excluded whale's tokens are burned through the hook, so configureEpoch()'s totalSupply()-totalExcludedSupply underflows and reverts permanently, freezing the 50,000e18 reward-USDC pool (rewards distribution can never be configured).

SOLIDITY

    function _handleOutflow(address from, uint256 amount) internal {
        AccountState storage s = accounts[from];
        s.balance -= amount; // @> BUG: excluded-account outflow never decrements totalExcludedSupply -> drift, then underflow DoS
    }

Why it's exploitable here#

Stale totalExcludedSupply (1,000,000e18) exceeds the shrunken totalSupply (100,000e18) after an excluded whale's tokens are burned through the hook, so configureEpoch()'s totalSupply()-totalExcludedSupply underflows and reverts permanently, freezing the 50,000e18 reward-USDC pool (rewards distribution can never be configured).

Attack path#

flowchart TD S0["Gate outflow hook to real holders"] S1["Outflow hook on burn or transfer"] S2["Cut balance, not excluded supply"] S3["Configure epoch reward distribution"] S4["Fixed rewards engine variant"] H["Stale totalExcludedSupply (1,000,000e18) exceeds the shrunken totalSup"] S0 --> S1 S1 --> S2 S2 --> S3 S3 --> S4 S4 --> H

Marked-line walkthrough (Playground)#

The EVM Playground pins each step to the exact executed source line in 0x671d353a77…:

  1. L160 — Gate outflow hook to real holders: Setup: only runs the outflow bookkeeping for genuine holders, skipping mints (from==0) and the token's own transfers.
  2. L168 — Outflow hook on burn or transfer: The per-holder bookkeeping hook that fires whenever from sends or burns tokens, meant to keep the reward accounting in sync.
  3. L170 — Cut balance, not excluded supply: Reduces the excluded holder's balance on burn but never decrements totalExcludedSupply, leaving that aggregate stale above totalSupply.
  4. L179 — Configure epoch reward distribution: Later computes totalSupply() - totalExcludedSupply; once the stale excluded figure exceeds real supply this underflows and reverts forever.
  5. L190 — Fixed rewards engine variant: Setup: the corrected RewardsEngineFixed contract used for comparison, which keeps excluded supply in sync on outflow.
  6. L197 — Per-account state mapping: Setup: stores each account's balance and exclusion flag used by the reward bookkeeping.
  7. L202 — Token-only access modifier: Setup: restricts the outflow hook so only the token contract may invoke it.

PoC#

Registry (Foundry, local deploy — verbatim vulnerable source + harm-asserting test + negative control):

BASH
cd 64666-totalexcludedsupply-drifts-from-reality-spearbit-none-buck-l_exp
forge test -vvv

The browser Playground replays the same synthetic opcode-for-opcode and measures the harm: Stale totalExcludedSupply (1,000,000e18) exceeds the shrunken totalSupply (100,000e18) after an excluded whale's tokens are burned through t. Both gates are green (registry forge test PASS + Playground _verify-poc VERDICT: PASS).

Sources & further analysis#

Reproductions & code

Alerts & third-party analyses

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