402Bridge Hit by $17K Exploit After Private Key Leak

Highlights:

• Hackers drained $17,000 in USDC through 402Bridge’s leaked private key.
• Over 200 users lost funds after granting contract approvals.
• 402Bridge halted operations and reported the breach to authorities.

The 402Bridge site has suffered a serious breach, leading to the loss of more than $17,000 to users in the USDC. This attack occurred just when the x402 protocol was gaining popularity within Web3. The suspicious transactions were first flagged by blockchain security firm PeckShield.

This incident impacted more than 200 users, which is one of the most alarming incidents of a newly launched protocol. Blockchain experts were quick to urge users to revoke any wallet authorizations connected to 402Bridge, which spread quickly through the crypto community.

#PeckShieldAlert @402bridge has been exploited. ~17K $USDC was stolen.

Please *Revoke* your allowance, if any, to 0xed1AFc4DCfb39b9ab9d67f3f7f7d02803cEA9FC5https://t.co/G07UxR0vYC https://t.co/7LmDVIKIpD

— PeckShieldAlert (@PeckShieldAlert) October 28, 2025

402Bridge Private Key Leak Caused Major Exploit

402Bridge disclosed that it was an exploit through a critical backend flaw. The team acknowledged that their system needed to store an admin key online. This placed the platform under high risk, as the key was used to manage contract methods.

The x402 model is based on transactions approved by users via a web interface. These permissions were then redirected to a backend that performs contract functions with the use of the admin key. The vulnerability was the key, which could be accessed online.

The x402 mechanism requires users to sign or approve transactions via the web interface, which are then sent to a backend server. The backend server extracts the funds and performs the minting, finally returning a result to the user.

When we onboard to https://t.co/RJ3Cz5txDh,…

— 402bridge (@402bridge) October 27, 2025

Upon gaining access, the attacker redirected user funds with the aid of the admin key. The wallet belonging to the attacker, 0x2b8F, drained about $17,693 in USDC. It then converted the stablecoins into 4.2 ETH. From there, the ETH was then transferred into various wallets and later transferred to the Arbitrum network. This chain of operations made the recovery and tracing of the funds virtually impossible.

Security Firms Urge Revocation of Authorizations

GoPlus Security and other blockchain security platforms encouraged users to revoke wallet permissions. They also stressed the use of official contract addresses only. Caution about approvals remains crucial, particularly when protocols store admin keys online. 402Bridge has since gone offline and halted operations. The protocol acknowledged in a statement saying, “The x402 protocol mandates that the admin key be stored in a back-end server. This can reveal administrative privileges.”

This vulnerability allowed a complete overhaul, enabling the attacker to redirect user funds freely. Security experts have since focused on the smaller approvals and regular review of wallet permissions. Moreover, the attack involved over a dozen wallets and team testing accounts. The team confirmed that the reason behind the leakage was a private key leak. The authorities have been informed, and investigations are underway.

Surge in x402 Use Coincided with Hack

Interestingly, the attack came soon after the x402 protocol spread widely in the crypto community. On October 27, the value of x402 exceeded 800 million, which is more attractive for exploiting the platform.

x402 model enables immediate payments of the stablecoins through the HTTP 402 status. Moreover, it facilitates not only machine-to-machine or human-administered API calls, unveiling use cases, but also exposes the gateway to vulnerability without solid key management. In September, the number of crypto hacks reached 20 incidents, amounting to $127 million. The activity has slowed down as compared to August, but the problem of poor key management remains a recurring issue.