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Reproduced Exploit

Terplayer: A staker's legitimate withdraw() reverts on arithmetic underflow: ceiling-division delegat

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: 62638-c-01-withdrawal-calculation-causes-underflow-locking-all-use. Standalone Foundry PoC and full write-up: 62638-c-01-withdrawal-calculation-causes-underflow-locking-all-use_exp in the evm-hack-registry mirror.

Vulnerability classes: vuln/locked-funds

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#

A staker's legitimate withdraw() reverts on arithmetic underflow: ceiling-division delegated shares over-count so totalDelegatedAmount exceeds amount and remainingAmount = amount - totalDelegatedAmount underflows (Panic 0x11), permanently locking the staked position (2 BVT blocked here) behind a reverting withdraw.

SOLIDITY
            address user = users[i];
            uint256 delegatedAmount = delegatedStakes[msg.sender][user];
            if (delegatedAmount > 0) {
                uint256 withdrawAmount = (delegatedAmount * amount + stakes[msg.sender] - 1)  / stakes[msg.sender]; // @> ceiling division: every per-delegatee term rounds UP, so the sum overshoots `amount`
                if (withdrawAmount > 0) {
                    totalDelegatedAmount += withdrawAmount;

Why it's exploitable here#

A staker's legitimate withdraw() reverts on arithmetic underflow: ceiling-division delegated shares over-count so totalDelegatedAmount exceeds amount and remainingAmount = amount - totalDelegatedAmount underflows (Panic 0x11), permanently locking the staked position (2 BVT blocked here) behind a reverting withdraw.

Attack path#

flowchart TD S0["Delegated users list param"] S1["Enter delegated withdrawal"] S2["Init delegated-sum accumulator"] S3["Ceiling division over-counts share"] S4["Add non-zero shares to total"] H["A staker's legitimate withdraw() reverts on arithmetic underflow: ceil"] 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. L87 — Delegated users list param: Setup: dUsers is the array of addresses the staker delegated to, iterated when splitting the withdrawal.
  2. L102 — Enter delegated withdrawal: _delegateWithdraw reclaims the staker's amount by portioning it back across each delegatee.
  3. L108 — Init delegated-sum accumulator: Starts totalDelegatedAmount at 0 to tally each delegatee's reclaimed share.
  4. L115 — Ceiling division over-counts share: Root-cause bug: the + stakes-1 ceiling division rounds every delegatee's withdrawAmount up, so the summed shares over-count the real amount.
  5. L116 — Add non-zero shares to total: Only non-zero withdrawAmount entries feed the running totalDelegatedAmount.
  6. L123 — Subtract inflated total — underflow: amount - totalDelegatedAmount underflows (Panic 0x11) because the rounded-up sum exceeds amount, reverting the whole withdraw.
  7. L138 — Staking token reference: Setup: bvt holds the MiniToken the vault stakes and would return on a successful withdraw.

PoC#

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

BASH
cd 62638-c-01-withdrawal-calculation-causes-underflow-locking-all-use_exp
forge test -vvv

The browser Playground replays the same synthetic opcode-for-opcode and measures the harm: A staker's legitimate withdraw() reverts on arithmetic underflow: ceiling-division delegated shares over-count so totalDelegatedAmount excee. 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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