A study presented at the USENIX Security Symposium identified 31 distinct vulnerabilities across the leading x402 protocol facilitators, including Coinbase, with validated attack paths that expose facilitator assets and enable unpaid purchases
Researchers tested 15 of the leading x402 facilitators – including Coinbase, Thirdweb, PayAI and Mogami – and found that every platform violated at least one security rule. The study, presented at the 35th USENIX Security Symposium, mapped 49 rule violations across 31 distinct vulnerabilities in systems that accounted for 99% of observed x402 transactions and 98% of payment volume during the period analysed.
The researchers identified four attack classes: free shopping, asset theft, service disruption, and network fee abuse. They directly validated six attack paths, including two free-shopping paths, three gas-abuse paths, and one that could expose assets held by facilitators. The most serious attack involved ERC-6492, an Ethereum signature standard for smart contract wallets: malicious metadata could lead a facilitator to fund and submit an arbitrary token-approval transaction in place of the expected payment.
Three further validated attacks exploited the network-fee sponsorship function: an attacker could force vulnerable implementations to pay for the deployment or initialisation of costly smart contracts. The researchers wrote that if facilitators sponsor fees without reliable reconciliation or chargeback capability, attacker-induced settlement can translate into a direct loss for the sponsor. The analysis covered more than 119 million x402 transactions on Base and Solana between 1 October and 26 December 2025: facilitators spent roughly 202,000 dollars in network fees, of which approximately 5,800 dollars were on Base transactions that were subsequently reversed or failed.
On the free-shopping front, all seven official Coinbase reference server kits examined lacked explicit mechanisms to roll back actions initiated after a successful verification. In Flask kit versions up to 0.2.1, protected resources could be released following verification regardless of whether the subsequent settlement succeeded. Merchant adoption of x402 was concentrated: more than 93% of the approximately 53,500 unique servers observed were associated with a single facilitator, with Coinbase alone processing 77.17 million transactions. A remediation update dated 6 February noted that Coinbase, PayAI and Mogami had collectively confirmed six vulnerabilities, some already resolved and others still in progress. The researchers did not publish a per-facilitator breakdown of vulnerabilities. Recommended countermeasures include treating all client-supplied transaction fields as untrusted, re-verifying payment conditions immediately before settlement, and enforcing strict limits on sponsored gas. The study also recommends that merchants delay irreversible services until settlement confirmation.
