402bridge Suffers Private Key Leak, Over 200 Users Lose USDC in Protocol Breach

Quick Breakdown 

• GoPlus detected a suspected exploit on x402bridge, leading to $17,000 in USDC losses.
• The breach originated from a private key leak tied to the project’s backend system.
• 402bridge has paused operations and reported the incident to law enforcement.

GoPlus flags suspicious activity on 402bridge

Web3 security firm GoPlus Security has issued a warning about an apparent exploit affecting x402bridge, a cross-layer payment protocol under the x402 ecosystem. The firm’s Chinese social media account revealed that the incident led to more than 200 users losing their USDC following unauthorized token transfers.

The breach, detected on October 28, occurred shortly after the protocol launched on-chain. According to GoPlus, the exploit stemmed from excessive user authorizations that allowed malicious transfers of stablecoins directly from connected wallets.

1/ #x402 大坑❗️ 过度（无限）授权要你命……

x402跨链协议 @402bridge 疑似被盗，合约 0xed1AFc4DCfb39b9ab9d67f3f7f7d02803cEA9FC5 的 Creator 把 Owner转给了0x2b8F95560b5f1d1a439dd4d150b28FAE2B6B361F，然后新 Owner调用合约中 transferUserToken 方法转移所有已授权用户钱包剩余的USDC。… pic.twitter.com/hegqhap3Od

— GoPlus中文社区 (@GoPlusZH) October 28, 2025

Attack vector: ownership transfer and exploited privileges

Blockchain data shows that the contract creator (address beginning with 0xed1A) transferred ownership to another address (0x2b8F), effectively granting it administrative privileges. These permissions allowed the new owner to modify key contract settings and execute sensitive functions.

Shortly after taking control, the exploiter triggered the “transferUserToken” function — draining all remaining USDC from wallets that had granted approvals to the protocol. In total, approximately $17,693 worth of USDC was stolen before being swapped for ETH and later bridged to Arbitrum through multiple cross-chain transactions.

GoPlus and security experts warn users

GoPlus urged users to immediately revoke any active authorizations related to 402bridge and verify all approved contract addresses. The firm reminded the Web3 community to avoid granting unlimited token allowances and to regularly audit wallet authorizations to prevent similar incidents.

Following the exploit, 402bridge confirmed the breach was caused by a private key leak that compromised several team wallets, including test and main accounts. The protocol has since halted all operations, taken its website offline, and reported the incident to law enforcement authorities.

In an earlier technical post, the team explained that the x402 mechanism relies on a web interface where users approve transactions. These approvals are relayed to a backend server that requires the admin’s private key to execute contract methods — a setup that inadvertently exposed sensitive admin credentials online.

The compromise enabled the attacker to assume full administrative control, redirecting user funds to malicious addresses. In March GoPlus security was listed on Binance following HODLer airdrop distribution.

 

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