Hack history / 2020 / Hack or exploit
Opyn
Hack or exploit on Aug 4, 2020 · Withdrawal Logic Flaw
ATTACK TX CONFIRMED ON CHAINSOURCES AGREE ON DATE AND LOSS · 3 SOURCES
Lost
$371K
dollars at the time
Returned
none listed
as the sources state it
Rank
#1,246
among thefts by dollars lost
What happened
The Opyn ETH Put contract had a critical bug in its exercise function: msg.value was checked inside a loop but only the first batch of ETH was actually received. Attackers called exercise() with multiple vaults in a single transaction, reusing the same ETH batch to withdraw collateral multiple times.
Details
- Date
- Aug 4, 2020
- Kind
- Hack or exploit
- Method
- Withdrawal Logic Flaw
- How in
- Smart contract bug
- Target
- DeFi protocol
- Chains
- Ethereum
Reported by
Related incidents
Opyn 2023 · Hack or exploit · undisclosed
Bisq 2020 · Hack or exploit · $248K
Soda Protocol 2020 · Hack or exploit · $160K
Bisq 2020 · Hack or exploit · $248K
Soda Protocol 2020 · Hack or exploit · $160K
Cite this page
SwanBluechip, "Opyn hack, Aug 4, 2020: $371K lost", Crypto hack history, https://swan-hack-tracker.pages.dev/history/i/ht591d297f16/ (data as of 2026-10-31).