The US authorities have seized about $31m in cryptocurrency connected to the 2021 Uranium Finance hack, marking a major breakthrough nearly four years after the attack.

The Southern District of New York (SDNY) announced the seizure in an X post on Monday, attributing the recovery to a coordinated effort with Homeland Security Investigations (HSI) in San Diego.

The hack, among the largest decentralized finance (DeFi) exploits at the time, targeted Uranium Finance—a platform built on the Binance Smart Chain and a fork of Uniswap. A critical flaw in its smart contract code was exploited during the platform’s migration to its V2.1 upgrade.

A Multi-Million Dollar Breach

The vulnerability, specifically a calculation error in the balance modifier logic, artificially inflated reported balances, allowing the hacker to drain liquidity pools. Losses amounted to a staggering $50m, with stolen assets including 80 BTC, 1,800 ETH, 17.9m BUSD, 5.7 million USDT, 638,000 ADA, 26,500 DOT, 34,000 wBNB and 112,000 of Uranium’s native token, U92.

Acting quickly, the perpetrator laundered the stolen funds, leveraging Tornado Cash, an Ethereum mixer, to obscure the transaction history, and AnySwap, a cross-chain bridge, to transfer assets from BSC to Ethereum.The exploit proved fatal for Uranium Finance, which ultimately shut down, leaving investors without immediate recourse.

Uranium Finance directly copied the automated market maker (AMM) Uniswap, deploying it on Binance’s BNB chain (then called Binance Smart Chain). In April 2021, a hacker exploited a bug in Uranium’s pair contracts to steal $50 million in various tokens. At the time of the incident, the Uranium Finance hack was one of the largest monetary exploits in decentralized finance (DeFi) history.

Suspicions Around Uranium Finance Hack.

The incident raised serious concerns about smart contract security in DeFi. Despite undergoing an audit, Uranium Finance’s code contained a subtle yet catastrophic bug. This flaw exposed weaknesses in its adaptation of Uniswap’s structure for BSC.

The timing of the attack added to suspicions. It occurred just days after the platform’s V2 deployment. Shortly after, Uranium’s contract repository was removed from GitHub, fueling speculation of an inside job. These concerns grew stronger as the platform had already suffered a $1.3 million breach earlier that month. This further intensified scrutiny of its security protocols.

Moreover authorities’ latest recovery efforts signal a significant step toward holding cybercriminals accountable in the evolving landscape of crypto fraud.