PoolTogether

What it is

PoolTogether is a no-loss prize savings protocol: deposits earn yield, the yield funds prizes, and a periodic draw decides who wins.

What was reviewed

One competition on the prize layer, May 2024, first place, over the prize pool, the draw auctions and the vault accounting.

What was found

12 findings, 2 of them high severity, and one of those was the only high severity issue in the competition that none of the more than 400 other participants found.

Featured finding

PoolTogether decides who wins by weighing what each vault contributed over a long stretch of past draws. Those contributions are kept in fixed size ring buffers, one for the running total and one for each vault, and the stretch is long enough that the total buffer has already wrapped and overwritten its oldest draw while the vault buffers have not. A vault was therefore measured over a longer period than the total it was being compared against, so its share of the prize came out larger than it had earned, and where the overwritten draw carried a donation the arithmetic underflowed and the prize could not be claimed at all.

As designedContributions are recorded per draw, in fixed size ring buffers↓A vault’s share is its contribution over a stretch of draws, against the total over the same stretch↓The two sides cover the same draws, so the shares sum to the whole

The path the bug allowedThe stretch reaches back to the buffers’ oldest draw↓The total’s buffer has wrapped and overwritten that draw; the vaults’ buffers have not↓A vault is measured over more draws than the total it is compared against↓Its share comes out larger than it earned, and where the lost draw held a donation the claim reverts

See the whole finding

Engagement history