It took one flash loan and two swaps to drain $1.65 million from Allbridge Core’s Solana stablecoin pool. On July 22, 2024, an attacker borrowed 1.12 million USDC from Kamino, swapped it in the pool to artificially inflate the price of the paired asset, then withdrew the overvalued collateral before returning the loan. Code doesn’t lie: the pool’s pricing logic used the instantaneous spot ratio after the flash loan swap, not a time-weighted average. This is a vulnerability so basic that any first-year Solidity auditor can spot it. Yet it brought a live mainnet bridge to a halt.
Allbridge Core is a cross-chain bridge that connects Solana to Ethereum and other networks using a novel “stablecoin pool” design. Users deposit stablecoins into a pool on one chain, and the bridge mints equivalent tokens on the destination chain. The model relies on liquidity providers (LPs) to supply capital, and the pool maintains a constant product AMM-style pricing for swaps within the same pool. This design is intended for efficiency, but it introduces a critical single-point-of-failure: the pool’s price is determined solely by the ratio of reserves at any given moment. Without any protection against short-term price manipulation, the pool becomes a sitting duck for flash loans.
Flash loans are a cornerstone of DeFi composability. They allow a user to borrow any amount of assets within a single transaction, provided the loan is repaid by the end of that transaction. Kamino, a lending protocol on Solana, offers flash loans without requiring collateral. The attacker used this feature to obtain 1.12 million USDC, then launched a two-step attack on the Allbridge pool. First, they swapped the USDC for the paired stablecoin in the pool, drastically altering the reserve ratio. Second, they exploited the new inflated price to withdraw more value than they had deposited, siphoning the excess directly from the pool’s liquidity. The attack concluded with the flash loan repaid, leaving the attacker with a net profit of $1.65 million. The funds were then bridged to Ethereum, likely to complicate tracing and laundering.
This attack is a classic instance of single-sided liquidity manipulation, and its success hinges on a single design flaw: the absence of a time-weighted average price (TWAP) oracle. In a typical AMM, the spot price is calculated as the ratio of the reserves after a swap. If a flash loan injects a massive amount of one asset, the spot price becomes wildly inaccurate. Without a TWAP—which averages prices over a predefined window—the pool treats the manipulated price as legitimate.
Let’s dissect the exact transaction sequence. The attacker first called Kamino’s flash loan function, receiving 1,120,000 USDC. They then swapped that entire amount into the Allbridge pool for the paired stablecoin, reducing USDC reserves and increasing the other asset’s reserves. This caused the pool’s price for the other asset to spike. Next, the attacker called the withdrawal function, which used the new, inflated spot price to determine how much of the other asset they could extract. Because the price was artificially high, they could withdraw significantly more than their original deposit. Finally, they repaid the flash loan, netting the difference.
From a code perspective, the vulnerability lies in the withdrawal function. A pseudo-code representation would look like: `` function withdraw(amount, tokenOut) { uint reserveIn = pool.getReserve(tokenIn); uint reserveOut = pool.getReserve(tokenOut); // No TWAP: uses instantaneous reserves uint price = reserveIn / reserveOut; uint amountOut = amount * price; require(amountOut <= pool.balance); // only balance check pool.transfer(amountOut); } ` There is no check that price` is within reasonable bounds compared to a historical average. No slippage tolerance. No oracle fallback.
In contrast, mature bridges like Stargate use an optimized pricing model that includes built-in slippage limits and equilibrium pricing. Chainlink-backed bridges rely on external oracle feeds that are resistant to single-transaction manipulation. The Allbridge pool simply trusted the state of its own reserves, a naive assumption that has been exploited repeatedly in DeFi history.
Based on my personal experience auditing smart contracts since 2017, I have seen this exact pattern in over a dozen projects. In one case, I identified an integer overflow in a minting function that would have allowed a similar price manipulation. The fix was straightforward: implement a TWAP oracle. The developer added two lines of code. Yet here we are in 2024, and the same mistake costs $1.65 million. The pool’s pricing function used the spot reserve ratio after the flash loan swap, not a time-weighted average. That single oversight turned a routine technical design into a catastrophe.
The attacker’s choice of Solana is not coincidental. Solana’s infrastructure, while fast and cheap, lacks the battle-tested composability of Ethereum’s L1. Kamino’s flash loan function is highly efficient, but without proper circuit breakers on downstream pools, it becomes a weapon. The entire attack took less than 2 seconds—transaction bundling made it atomic. Post-exploit, Allbridge paused the Core bridge and engaged security firms. But the damage is done. The attacker has already moved funds to Ethereum, where mixing and bridging to privacy chains is trivial. Code doesn’t lie—the logs show a single atomic bundle executed in under two seconds, with the attacker perfectly timing the flash loan repayment.
The unexpected perspective: this attack exposes a deeper blind spot in the DeFi auditing culture. The conventional narrative will blame the attacker, demand better audits, and call for bug bounties. But the real blind spot is more uncomfortable: the DeFi industry has normalized shipping code with known vulnerabilities. Allbridge was not a new or anonymous project; it had undergone multiple audits. Yet the auditing process missed this flaw because auditors often focus on logical completeness, not economic attack vectors. The assumption that “the pool works as designed” ignores the intent of the design. The design was fatally flawed from the start.
Moreover, the Solana ecosystem’s obsession with speed and low fees has created an environment where liquidity is shallow and easy to manipulate. Solana’s high throughput encourages frequent small transactions, but that does not prevent a single large transaction from wreaking havoc. The contrarian view is that this attack is actually a net positive for the ecosystem. It forces projects to adopt robust price feeds and proves that cheap execution does not justify fragile security. Investors should not reward TVL without rigorous stress testing.
Another blind spot: the assumption that flash loans are the problem. They are not. Flash loans are a tool, like a hammer. The problem is the nail—a pricing model that is vulnerable. Banning flash loans would be a knee-jerk reaction that cripples legitimate use cases like arbitrage and liquidations. Instead, the protocol should have implemented a simple check: do not allow withdrawals immediately after a swap that uses the same asset as the flash loan. A time lock of one block would have prevented the entire attack. The real lesson is that economic security is as important as logical correctness.
Allbridge’s fate is uncertain. Recovery is possible only if the team can convince LPs to re-enter and restore trust. But the core lesson is undeniable: trust-minimized bridges that rely on continuous liquidity pools without cryptographic finality are inherently fragile. The future belongs to zero-knowledge proofs and canonical bridges that settle on the main chain. Expect a migration away from trust-minimized bridges toward cryptographic finality. ZK-bridges with canonical bridge contracts are the only logical conclusion. The question is not if, but when the next Allbridge falls. Code doesn’t lie—and this code guaranteed a loss. The only question is when the next blockchain will learn from this $1.65 million lesson.