TECH Signal 141
Symbiosis DeFi exchange loses at least $770,000 due to missing bounds checking in smart contract
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A hacker exploited a privilege escalation bug and a negative transaction fee vulnerability to mint 46 billion fake syBTC tokens and drain liquidity pools.
The event highlights how a basic failure to validate that a transaction fee is a positive number can lead to catastrophic fund drainage. It demonstrates the risk of open-source smart contracts where privilege escalation can allow attackers to manipulate core system logic.
Written by elseif from the cluster below · every claim links back to a sourceThe three things worth knowing
The attacker used an undisclosed privilege escalation exploit to gain network administrator rights.
A lack of bounds checking allowed the attacker to set transaction fees to negative values, adding to the moved amount instead of deducting from it.
The thief minted 46 billion syBTC using only 330 satoshi, subsequently trading them for wrapped BTC pairs to steal at least $770,000.
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The exploit occurred on September 11 when an attacker combined two vulnerabilities. First, a privilege escalation bug granted the attacker administrator access. Second, the smart contract failed to verify if transaction fees were positive numbers, allowing the attacker to set a negative fee that increased the total amount of tokens issued during 12 transactions.
By spending approximately 25 cents, the attacker minted 46 billion syBTC. While these tokens lacked backing, they were tradable against wrapped pairs including BTCB, cbBTC, WBTC, and RBTC. This process drained the liquidity pools, resulting in a loss of 9.97 BTC, though the attacker only successfully converted about $336,000 into cash via Uniswap.
Recovery of the funds varies by token type. Centralized entities like Coinbase can nullify and re-mint cbBTC through legal processes, but other tokens like RBTC cannot be recovered this way. Symbiosis intends to repay debts through a combination of evacuated funds and individual compensation plans for liquidity providers.
To prevent recurrence, Symbiosis is rewriting its Bitcoin-side logic and has requested independent audits of the new code and the entire system. The project noted that AI models have reduced the cost of finding such bugs, though the vulnerability stemmed from a fundamental coding failure to check for negative values.
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