The DAO: an attacker uses the contract's own logic to drain a third of its funds; the network reverses it by hard fork, June to July 2016
The typed evidence object. This is the working store; the case page is the reader's form.
| Layer / facet | Value | Type | Sources | Conf. |
|---|---|---|---|---|
| Mandate: principal | Token holders voted on proposals, but the SEC found that Slock.it, its co-founders, and the DAO's Curators made significant managerial efforts, and that the Curators kept ultimate control over which proposals went to a vote | fact | SEC, Report of Investigation Pursuant to Section 21(a) of the Securities Exchange Act of 1934: The DAO, Release No. 81207 | high |
| Mandate: objective | Hold contributed funds and release them to projects approved by holder vote | fact | SEC, Report of Investigation Pursuant to Section 21(a) of the Securities Exchange Act of 1934: The DAO, Release No. 81207 | high |
| Actor | The DAO contract | fact | SEC, Report of Investigation Pursuant to Section 21(a) of the Securities Exchange Act of 1934: The DAO, Release No. 81207 | high |
| Inputs | Transactions from an attacker who called The DAO's split function recursively, from inside the split itself, collecting ether many times in one transaction; the SEC's report describes it as a flaw in The DAO's code | fact | Ethereum Foundation blog, "CRITICAL UPDATE Re: DAO Vulnerability" (Vitalik Buterin), 17 June 2016; SEC, Report of Investigation Pursuant to Section 21(a) of the Securities Exchange Act of 1934: The DAO, Release No. 81207 | high |
| Decision | The contract executed as written: the recursive call let the attacker collect ether many times in one transaction | interpretation | Ethereum Foundation blog, "CRITICAL UPDATE Re: DAO Vulnerability" (Vitalik Buterin), 17 June 2016 | high |
| Envelope: constraints | The code was the envelope; as written, it permitted the drain, through what the SEC's report calls a flaw in The DAO's code | interpretation | SEC, Report of Investigation Pursuant to Section 21(a) of the Securities Exchange Act of 1934: The DAO, Release No. 81207 | high |
| Action | About 3.6 million ether, a third of the DAO's funds, moved into a child contract | fact | SEC, Report of Investigation Pursuant to Section 21(a) of the Securities Exchange Act of 1934: The DAO, Release No. 81207; Ethereum Foundation blog, "CRITICAL UPDATE Re: DAO Vulnerability" (Vitalik Buterin), 17 June 2016 | high |
| Outcome | State: harm, then reversed for most holders. Funds restored by the fork on one chain; the other chain kept the original history. As of 2017. | fact | Ethereum Foundation blog, "Hard Fork Completed" (Vitalik Buterin); SEC, Report of Investigation Pursuant to Section 21(a) of the Securities Exchange Act of 1934: The DAO, Release No. 81207 | high |
| Evidence: event | Fully visible on the public ledger | fact | Ethereum Foundation blog, "Hard Fork Completed" (Vitalik Buterin); Ethereum Foundation blog, "CRITICAL UPDATE Re: DAO Vulnerability" (Vitalik Buterin), 17 June 2016 | high |
| Evidence: actor | The SEC's report refers only to 'an unknown individual or group'; no authority has named the attacker. In February 2022 a journalist's investigation named a suspect, who denied it | assertion | SEC, Report of Investigation Pursuant to Section 21(a) of the Securities Exchange Act of 1934: The DAO, Release No. 81207; Decrypt, 'Former Crypto CEO Denies Responsibility for $11 Billion Ethereum DAO Hack', 22 February 2022 (reports a journalist's identification of a suspect and the suspect's denial) | medium |
| Recovery: automated fallback | A built-in holding period delayed withdrawal, which created the window for a response | fact | SEC, Report of Investigation Pursuant to Section 21(a) of the Securities Exchange Act of 1934: The DAO, Release No. 81207 | high |
| Recovery: technical | A hard fork of the network, adopted by majority of participants, moved the funds to a recovery contract; a minority chain refused | fact | Ethereum Foundation blog, "Hard Fork Completed" (Vitalik Buterin); EIP-779: Hardfork Meta: DAO Fork (block 1,920,000) | high |
| Recovery: accountability | No individual held liable. The SEC found that DAO Tokens were securities, whose offer and sale had to be registered unless an exemption applied; its report makes no finding of a violation by any individual or entity, and the SEC decided not to pursue an enforcement action | fact | SEC, Report of Investigation Pursuant to Section 21(a) of the Securities Exchange Act of 1934: The DAO, Release No. 81207 | high |
Controls
| Status | Control | Canonical |
|---|---|---|
| failed | Security review of The DAO's code before launch: Slock.it said a leading security audit company had reviewed it, yet the code held the flaw the attacker used; no source says whether the review covered the split function | C-D1 Pre-execution validation |
| failed | The code was the only enforced rule: the SEC report says The DAO's code 'was to govern how The DAO was to operate' and quotes The DAO's website describing it as 'operating solely with the steadfast iron will of unstoppable code'; the Curators, on whom the website said The DAO relied for 'failsafe protection', controlled which proposals reached a vote, and no source says a Curator could stop a split | C-M2 Machine-enforceable scope |
| succeeded | Holding period (delay before irreversibility); Community-level override | C-R3 Human takeover with a time window |
| absent | Pause or circuit-breaker in the contract | C-X2 Kill switch faster than the actor |
| absent | Withdrawal limits | C-X1 Rate and magnitude limits |
Inference
inference An attacker used a flaw in The DAO's code, a recursive call to its split function, to move about a third of its ether; the contract did what its code allowed. The code then held the moved ether for 27 days, which left time to respond. The response came from outside the code: DAO Token holders could not effectively deal with the attack without Slock.it and others, and a hard fork of Ethereum, adopted by a majority of the network, moved the funds to a recovery contract, while a minority kept the original chain. The record does not show whether a pause or a withdrawal limit in the contract would have prevented or reduced the loss.
Sources
| ID | Record | Type | Link |
|---|---|---|---|
| CHAIN | Ethereum Foundation blog, "Hard Fork Completed" (Vitalik Buterin) | company primary record | blog.ethereum.org ↗ checked 2026-10-13 |
| SEC-DAO | SEC, Report of Investigation Pursuant to Section 21(a) of the Securities Exchange Act of 1934: The DAO, Release No. 81207 | regulator primary record | sec.gov ↗ checked 2026-10-13 |
| EIP-779 | EIP-779: Hardfork Meta: DAO Fork (block 1,920,000) | standards body primary record | eips.ethereum.org ↗ checked 2026-10-13 |
| EF-CRIT | Ethereum Foundation blog, "CRITICAL UPDATE Re: DAO Vulnerability" (Vitalik Buterin), 17 June 2016 | company primary record | blog.ethereum.org ↗ checked 2026-10-19 |
| DECRYPT-DAO | Decrypt, 'Former Crypto CEO Denies Responsibility for $11 Billion Ethereum DAO Hack', 22 February 2022 (reports a journalist's identification of a suspect and the suspect's denial) | press pointer secondary: press report | decrypt.co ↗ checked 2026-10-19 |