On October 6, 2022, an attacker used a flaw in BSC Token Hub’s cross-chain proof verification to make the bridge accept unauthorized transfers. BNB Chain reported that 2 million BNB were withdrawn, but that was the gross amount—not the amount that ultimately escaped: estimates put the value moved off BNB Smart Chain at about $100 million to $110 million.
What was compromised—and what was not
The target was BSC Token Hub, the bridge connecting BNB Beacon Chain and BNB Smart Chain. A bridge uses evidence, or a proof, that an event occurred on one blockchain before it releases or creates corresponding value on another. In this case, the bridge accepted a forged proof and processed transfers that had not been authorized.
The incident was a bridge proof-verification failure, not evidence that every part of BNB Chain or the underlying cryptographic hash function had been broken. BNB Chain said the problem was limited to the bridge and that the chain was not rolled back.
How the forged proof passed verification
The flaw was in checking the proof
The attack exploited a weakness in IAVL proof verification. Coinbase Threat Intelligence’s October 31, 2022 technical investigation explained that, under the relevant condition, the verification logic did not include an already-defined right leaf in a hash calculation when the left leaf was defined. An attacker could add a leaf containing a fabricated transfer-payload hash and alter a previously valid proof so the bridge treated it as valid.
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After the proof passed, the CrossChain and TokenHub contracts executed the unauthorized transfer. The issue was therefore in how the proof was verified—not a break of the cryptographic hash itself.
Two transactions, one exploit
Coinbase’s analysis traced two successful exploit transactions on October 6, 2022: the first for 1 million BNB at 18:26:46 UTC and the second for 1 million BNB at 20:43:18 UTC. Together, those transactions account for the 2 million BNB gross withdrawal reported by BNB Chain.
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How much was taken?
The figures differ because sources reported at different times and used different valuations. The 2 million BNB figure describes the gross amount withdrawn through the exploit. The smaller dollar figures below refer to the amount reported as having moved off BNB Smart Chain after the response—not to the value of all 2 million BNB.
| Source and date | Gross amount | Value moved off-chain or unrecovered | What the figure means |
|---|---|---|---|
| BNB Chain, October 11, 2022 | 2 million BNB, valued at nearly $570 million | About $100 million unrecovered off-chain | BNB Chain’s reported valuation and estimate at that time. |
| Coinbase Threat Intelligence, October 31, 2022 | 2 million BNB, valued at about $586 million | Approximately $110 million taken off BNB Smart Chain | Coinbase’s valuation and estimate, reported later than BNB Chain’s figures. |
These estimates should not be collapsed into a single definitive loss number: the cited sources do not establish one universal dollar figure. In particular, describing the incident as a $570 million or $586 million theft would confuse the gross value of the BNB withdrawn with the smaller amount estimated to have escaped to other networks.
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How BNB Chain contained the incident
BNB Chain coordinated with validators to pause BNB Smart Chain while it addressed the exploit. Its October 7, 2022 update said 26 of 44 validators were active at the time and described contacting validators individually. The chain later resumed after the response and upgrade process.
On October 11, BNB Chain said, “The BNB Chain was never rolled back.” It also said no users were affected. That is the chain’s statement about user impact, rather than a separate independent audit conclusion. Coinbase documented a hard fork and patch. Binance subsequently reported that 1.02 million incident-related BNB had been locked by validator vote and burned; it said the remainder would be burned through the usual process.
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Incident timeline
| Date | What happened |
|---|---|
| October 6, 2022 | Coinbase’s investigation timestamps the two successful 1-million-BNB exploit transactions at 18:26:46 UTC and 20:43:18 UTC. |
| October 6–7, 2022 | BNB Chain coordinated a temporary pause with validators. Its October 7 account said 26 of 44 validators were active at the time and that the team had contacted validators one by one. |
| October 7, 2022 | BNB Chain published its initial incident account and said a more detailed postmortem would follow. |
| October 11–12, 2022 | BNB Chain described the pause and response on October 11. Binance announced support for a network upgrade and hard fork scheduled for about October 12 at 08:00 UTC. |
| January 17, 2023 | Binance reported that 1.02 million incident-related BNB had been locked following a validator vote and burned. |
What the incident shows about cross-chain bridges
A bridge depends on its verification rules to distinguish genuine cross-chain activity from a forged request. Here, a flaw in that logic let a manipulated proof pass, after which the bridge contracts carried out unauthorized transfers. The case illustrates why a bridge’s proof-checking code is a critical security boundary: correct hash functions alone cannot protect a system if the logic applying them checks the wrong data.
Pausing the chain required coordination with validators, which BNB Chain described as contacting them individually. That response helped contain the incident, but it also shows the practical tension between rapid intervention and a network’s ability to operate without centralized control. BNB Chain said the chain was not rolled back; the available incident accounts do not establish a quantified, lasting effect on users.
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Who was responsible?
Coinbase’s October 31, 2022 investigation did not identify the responsible actor or actors. The incident accounts cited here establish the technical method and response, but not the attacker’s identity.
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