Technical Root Cause: Deterministic Nonce
Published 6/25/2026, 1:53:31 PM
On June 23, 2026, the Cardano-based wallet provider SecondFi (formerly known as Yoroi) suffered an exploit resulting in the loss of approximately $2.4 million (16 million ADA). While the initial theft was limited, the total value at risk was significantly higher, with approximately 129 million ADA (~$20 million) eventually secured through emergency rescue operations [Source: https://www.coindesk.com/business/2026/06/24/secondfi-loses-usd2-4-million-in-cardano-wallet-exploit-with-up-to-usd20-million-at-risk].
Technical Root Cause: Deterministic Nonce Derivation
The exploit was not a breach of the Cardano protocol itself, but a critical failure in SecondFi's proprietary wallet-generation and signing software. The vulnerability stemmed from a deterministic nonce derivation flaw during the transaction signing process.
- Predictable Randomness: Instead of using true cryptographic randomness (PRNG) for every transaction, the software used recognizable patterns to generate nonces.
- Key Reconstruction: Because these nonces were deterministic, attackers could mathematically reconstruct a wallet's private key using only publicly available data from the Cardano blockchain.
- Activation: The vulnerability was "activated" whenever a user signed a transaction. Each signature provided the necessary mathematical variables for an attacker to derive the private key for that specific address.
Attack Mechanics and Timeline
The attack was executed in waves, beginning on June 21, 2026, and concluding with a "white hat" rescue operation by the SecondFi team to prevent further losses.
| Phase | Wallets Affected | ADA Amount | Outcome |
|---|---|---|---|
| Wave 1 (Malicious) | 198 | ~12.3M ADA | Liquidated via Minswap and other DEXs. |
| Wave 2 (Malicious) | 2,874 | ~129.4M ADA | Moved to a single vault address; later secured. |
| Rescue (White Hat) | ~374 | ~129M ADA | Funds routed to an independent custodian. |
Attackers monitored the mempool for transactions signed by SecondFi wallets and derived private keys for the first/default address (index 0) of those wallets. Stolen assets included 3,838 distinct token types, notably 20M NIGHT and 263M SNEK [Source: https://finance.yahoo.com/markets/crypto/articles/cardano-project-secondfi-hit-major-091625747.html].
Exposure and Disputed Figures
There is conflicting data regarding the total exposure. While some early reports suggested figures as high as $200 million, verified data indicates the total potential exposure was closer to $20 million (129M ADA) based on an ADA price of approximately $0.15 at the time [Verified: https://www.coindesk.com/business/2026/06/24/secondfi-loses-usd2-4-million-in-cardano-wallet-exploit-with-up-to-usd20-million-at-risk].
Security Implications for Users
Security researchers from SlowMist and Coinspect issued the following guidance:
- Hardware Wallets: Users who utilized SecondFi in conjunction with a hardware wallet (Ledger, Trezor, Keystone) were not affected, as private keys never left the hardware device and were not subject to the software's signing flaw.
- Address-Level Risk: The risk is specific to addresses that have previously signed transactions. Dormant addresses that have never sent a transaction are technically safe until they attempt to sign one.
- Restoration Warning: Simply restoring an affected seed phrase into a different wallet (like Eternl or Lace) does not resolve the issue, as the same compromised private key will be recreated [Source: https://99bitcoins.com/].
The incident remains a significant example of how implementation flaws in wallet software can expose private keys even when the underlying blockchain protocol remains secure. While the technical mechanism (deterministic nonces) is identified, it remains unclear whether the flaw originated from a specific code implementation error or a lack of proper randomness library usage.