SafeDollar Algorithmic Stablecoin Collapse

On June 28, 2021, the Polygon algorithmic stablecoin SafeDollar lost approximately $248,000 through a reward-calculation flaw that let the attacker drain the protocol's SDO/USDC reserves. The SDO stablecoin depegged to near zero.

What happened

SafeDollar's staking/reward logic mis-accounted reward issuance, allowing repeated extraction of protocol reserves disproportionate to legitimate entitlement. The reserve drain destroyed the backing assumptions of the SDO peg; SDO collapsed.

Aftermath

• Protocol effectively ended; SDO did not recover its peg.

Why it matters

SafeDollar is a small but representative member of the algorithmic-stablecoin-killed-by-a-mint/reward-bug family: Cashio, MobiusDAO, Raft, Zunami. The recurring structural truth: for a stablecoin, an exploit that breaks the peg is fatal even when the dollar amount is small — the product is the peg, and a demonstrated path to unbacked supply destroys it regardless of how much was actually extracted. SafeDollar's $248K is tiny; the protocol still died, because credibility, not capital, is a stablecoin's load-bearing asset.