Slope Wallet hack — August 2022

Beginning at 22:37 UTC on 2 August 2022 an attacker emptied thousands of Solana wallets over roughly four to seven hours. The Solana Foundation counted about 9,231 drained wallets and around $4.1 million in assets. Slope's own report put it at 9,229 wallets and roughly $4 million. Elliptic and AnChain told The Block the figure was at least $5 million.

The transactions were properly signed, which pointed at key material rather than a protocol flaw. Solana Labs and the Solana Foundation said no core Solana code was involved. Researchers at Otter Security found that Slope's mobile wallet apps for iOS and Android were transmitting users' mnemonic seed phrases in plaintext to a Sentry application-monitoring instance Slope ran itself, at o7e.slope.finance. Sentry later stated that its own SaaS product and infrastructure were not involved and that the host in question was a self-hosted deployment. Slope's digital-forensics report attributed the exposure to two unrelated mistakes: a toString() method added on 24 June 2022 that defeated Sentry's sensitive-data scrubbing, and plaintext logging introduced to speed up decryption for an encrypted-messaging feature. Because Solana and Ethereum both use BIP39 mnemonics, users who reused a Slope seed phrase in Phantom or Solflare, or on Ethereum, were also exposed. Hardware wallets were unaffected.

The causal link is disputed. Slope said private keys for 6,811 wallets were found on its Sentry database but that only 1,444 of those were among the 9,229 wallets actually drained, and audits by OtterSec and SlowMist found no conclusive evidence tying the Sentry exposure to the drain. Slope shut down the Sentry server on 3 August, pulled its mobile apps on 5 August and told users to abandon the affected addresses.