How user misoperation can trigger a $240,000 flash loan attack: DeFi risks behind the SEI chain security incident

SEI Chain遭遇24万美元闪电贷攻击，攻击者通过Synnax合约借出196万枚WSEI后未归还。但这起事件的关键在于，攻击的触发点并非智能合约漏洞，而是一笔用户的链上误操作。这提醒我们，DeFi的安全风险不仅来自代码层面，更来自用户操作的细节。

How the attack happened

According to BlockSec Phalcon’s monitoring, the full chain of this attack is as follows:

User error as the breaking point

Address 0x9748…a714 made a mistake three blocks ago — mistakenly transferring funds into the Synnax contract. This misoperation might have been just an ordinary user mistake, but it unexpectedly provided the funds for the subsequent attack. The most noteworthy part of this incident: the attacker did not exploit a complex contract vulnerability but utilized an existing on-chain mistransfer of funds.

Lightning loan “borrowed without repayment”

The attacker then initiated a flash loan via the Synnax contract, borrowing 1.96 million WSEI (about $240,000). The characteristic of a flash loan is that borrowing and repayment are completed within the same transaction, but this time, the attacker chose not to return the funds. What does this mean? Either the contract itself has a vulnerability allowing non-repayment, or the attacker exploited a specific logical flaw. According to the latest news, the attack involved two transactions, TX1 and TX2, indicating a multi-step coordinated operation.

The invisible killer of DeFi security

This incident reveals a very real but often overlooked risk:

Irreversibility of on-chain operations

Transfers on the blockchain are irreversible. When a user mistakenly transfers funds to a contract address, those funds are usually gone forever. In this case, it was precisely because of this mistransfer that the attacker had a foothold. This is not a contract design issue but a user operation risk.

Chain reaction of user errors

A user’s mistake can be exploited by hackers as a trigger for larger-scale attacks. This “passive participation” risk is hard to prevent — victims may not even realize their mistake could lead to such consequences.

Flexibility of the flash loan mechanism

Flash loans are an innovative product of DeFi, allowing large loans within a single transaction without collateral. But this flexibility can also be exploited by attackers. If the contract lacks strict repayment checks or has logical vulnerabilities, attackers can execute “borrow without repayment.”

Impact assessment on the SEI ecosystem

From the timing, this security incident occurred during a very active phase of the SEI ecosystem. Recent reports indicate that Crypto.com and SEI officials just launched a 7% annualized yield staking activity, and USDC.n is undergoing migration incentives. SEI’s price has also recently shown an upward trend.

How will this attack affect ecosystem confidence? Currently, the loss amount is relatively limited ($240,000) and was quickly detected. The key is how SEI officials and the Synnax team respond. If they can quickly identify the issue, compensate victims, and improve protections, the negative impact will be limited. But improper handling could undermine new users’ confidence in the SEI ecosystem, especially those who just decided to participate in staking.

What users need to know

Think before transferring

Before transferring on-chain, always verify the recipient address. Especially when interacting with smart contracts, ensure you are transferring to the correct contract address. Once transferred, there is no opportunity to undo.

Understand your risks

Participating in DeFi requires understanding not only the project’s security but also the risks brought by mechanisms like flash loans and smart contracts. Security incidents can originate from multiple layers — code vulnerabilities, user operations, or even ecosystem participants’ mistakes.

Pay attention to official responses

When a security incident occurs, quick response and transparent communication from the project team are crucial. Will SEI release detailed incident analysis? Will they compensate victims? These are indicators of the project’s security awareness.

Summary

This $240,000 SEI chain flash loan attack is essentially a “triangle” risk overlay: user on-chain error, the flexibility of flash loans, and possible contract logic vulnerabilities. The most concerning aspect is not how complex the attack itself is, but how an ordinary user’s mistake can trigger a large-scale attack. It reminds all DeFi participants that security precautions must start from every operation. The SEI ecosystem is growing, and such security incidents are part of the growth process — the key is how the official response and improvements are handled.