SEI Chain Faces Flash Loan Vulnerability: Synnax Contract Breach Exposes New Attack Vector

Flash loan attacks continue to plague the DeFi ecosystem, and SEI chain has become the latest victim. However, Synnax contract’s recent security incident reveals a nuanced threat—sometimes the biggest vulnerability isn’t in the code itself, but in how users interact with it.

The Attack Breakdown

According to findings by BlockSec Phalcon, an attacker exploited a flash loan mechanism to extract 1.96 million WSEI tokens from the Synnax contract, representing approximately $240,000 in value. What makes this incident particularly noteworthy is that the attacker never intended to repay the borrowed funds, executing a complete capital drain rather than a typical arbitrage-based flash loan attack.

The Unexpected Catalyst

The real story, however, begins three blocks earlier. An address (0x9748…a714) inadvertently transferred a substantial amount of funds directly into the contract through what appears to have been a user error. This misrouted transaction essentially pre-loaded the Synnax contract with the capital needed to execute the subsequent flash loan attack. The incident highlights a critical pattern: user mistakes can become attack enablers.

Attack Chain and Technical Insights

The exploit was executed through two primary transactions (TX1 and TX2), demonstrating how attackers chain operations together to maximize extraction efficiency. The transactions unfolded in a coordinated sequence that left minimal room for detection or intervention.

Broader Risk Implications

This SEI chain incident serves as a reminder that DeFi security isn’t solely about smart contract audits. Chain misoperations—whether accidental fund transfers or improper parameter settings—can create unexpected attack vectors that security reviews might overlook. As the ecosystem matures, protecting against both code vulnerabilities and operational errors becomes equally critical.