bulikos / bsc-hack-analysis-2022-10-06

BSC HACK ANALYSIS 2022-10-06

This material is just for educational purposes for the issue

analysis

tldr

exploiter leveraged a bug (1) in the merkle proof verification logic (2) adapting a proof from one of the very first cross chain tx (3) which was minting 0.05 BNB to Binance Deployer 1 (4)

samczsun described the process in this thread (5). you can forge a proof for any payload.

longer

exploiter forged proof steps:

• start from the legit proof (3)
• injecting a leaf node containing as Key the current packageSequence and as Value the evil payload hash (i.e. minting 1M BNB to their address)
• add an empty inner node to the leaf (see diff - iavlproof1 and iavlLegitProof.png)
• set in the left path as Right the hash of the leaf node just created

In this way the evil payload looks legit and pass the verification.

exploiter had success for the first time with this tx (6) but then failed 15 times (check notes) because they had competition with other legit bridge txs. at some point they were able to mint another time (7).

the specific choice of this so low height (110217401) can be related to the preparation of the tx, which has the same parameters of the one (3) containing the legit proof.

refs

• (1) https://twitter.com/dedaub/status/1578428002701959170
• (2) https://github.com/cosmos/iavl/blob/de0740903a67b624d887f9055d4c60175dcfa758/proof_range.go#L219
• (3) https://bscscan.com/tx/0x79575ff791606ef2c7d69f430d1fee1c25ef8d56275da94e6ac49c9c4cc5f433
• (4) https://bscscan.com/address/0x4e656459ed25bf986eea1196bc1b00665401645d
• (5) https://twitter.com/samczsun/status/1578182840751050752
• (6) https://bscscan.com/tx/0xebf83628ba893d35b496121fb8201666b8e09f3cbadf0e269162baa72efe3b8b
• (7) https://bscscan.com/tx/0x05356fd06ce56a9ec5b4eaf9c075abd740cae4c21eab1676440ab5cd2fe5c57a

content

• sam.go, original samczsun POC
• evilPayloadGenerator.go, forged proofs builder
• in the txts various representation of some proofs

todo

• get failed tx x
• compare data x
• print evl trees x
• reverse engineer the hack x
• script to generate evil payload x
• understand where the original payload comes x

notes

hacker address 0x489a8756c18c0b8b24ec2a2b9ff3d4d447f79bec

first mint

https://bscscan.com/tx/0xebf83628ba893d35b496121fb8201666b8e09f3cbadf0e269162baa72efe3b8b

second successful mint

https://bscscan.com/tx/0x05356fd06ce56a9ec5b4eaf9c075abd740cae4c21eab1676440ab5cd2fe5c57a

failed txs (15)

https://bscscan.com/tx/0xf2c714b6b006fc9c633d5d95ddec05a76402f9607e114fcece30656f25047dc9 https://bscscan.com/tx/0x37cbd83dd92614943cb4675b3d1056e023ab521f7c064470f7e869b13e91cdd7 https://bscscan.com/tx/0xcc5cf14ed103b90bdcd95d21f1c8e73a6fcbf6da55574f5add88d51f63edfe62 https://bscscan.com/tx/0x15069bd1647786212d029e1d169d8aa830bd88d9c8b8c8e1cee2e44d02040671 https://bscscan.com/tx/0x26a6514557df1c28333d545e0ac7cb084fd1a949e2fa89e28c9d0336ab02260b https://bscscan.com/tx/0x069bbd81b1367fc7f15d13d8ce66e8b23149228b31d249d7b2f66c239f6e8a00 https://bscscan.com/tx/0x917624bfda3bea78cfc7459bb96b0601ebb21ba0bb7c83f8641e62d138b0e277 https://bscscan.com/tx/0x1c2e7942f2977e97479bdefeacafd959836161033013cbfc93d76c2195c0bdfc https://bscscan.com/tx/0xd1611ec1c0a0c8a54df18d4c937acc95b9f4bb737e61bd4dfa2e8350e138dd05 https://bscscan.com/tx/0x9613e6e62125e59fba71dbd93ec1b274da1552c88d086768d3def302b2f5ba78 https://bscscan.com/tx/0xda9e25e4b7aa6c0259c2b2174cdb3edf8a7db9a235cdb1c0c5880d7a8f1793e9 https://bscscan.com/tx/0xa6259fea1f825bca96188c909abab5d6864c2df73b7d7803dcb4c7fb4aef2ace https://bscscan.com/tx/0xb050ddd09144984ce18e885ffc051af74b4b711e605a37a3f165a456e02b13a5 https://bscscan.com/tx/0x8bc62a475f9c1df926de69f7117d67449afe3fe57b9daf5f7bceeffc56c991ba https://bscscan.com/tx/0xcf127483bd05d5cfb4ee6d113dcabe7b7c3c45ae3eb7c65efb4a687c6161c9f7

analysis

first mint

input precompile contract 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

https://bscscan.com/tx/0xf2c714b6b006fc9c633d5d95ddec05a76402f9607e114fcece30656f25047dc9

payload: 0x000000000000000000000000000000000000000000000000000000000000000000f870a0424e4200000000000000000000000000000000000000000000000000000000009400000000000000000000000000000000000000008ad3c21bcecceda100000094489a8756c18c0b8b24ec2a2b9ff3d4d447f79bec94489a8756c18c0b8b24ec2a2b9ff3d4d447f79bec846553f100 proof: 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 packageSequence:17684857 (00000000010dd979) height:110217401

https://bscscan.com/tx/0x37cbd83dd92614943cb4675b3d1056e023ab521f7c064470f7e869b13e91cdd7

payload: 0x000000000000000000000000000000000000000000000000000000000000000000f870a0424e4200000000000000000000000000000000000000000000000000000000009400000000000000000000000000000000000000008ad3c21bcecceda100000094489a8756c18c0b8b24ec2a2b9ff3d4d447f79bec94489a8756c18c0b8b24ec2a2b9ff3d4d447f79bec846553f100 proof: 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 packageSequence:17684867 (00000000010dd983) height:110217401

https://bscscan.com/tx/0xcc5cf14ed103b90bdcd95d21f1c8e73a6fcbf6da55574f5add88d51f63edfe62

payload: 0x000000000000000000000000000000000000000000000000000000000000000000f870a0424e4200000000000000000000000000000000000000000000000000000000009400000000000000000000000000000000000000008ad3c21bcecceda100000094489a8756c18c0b8b24ec2a2b9ff3d4d447f79bec94489a8756c18c0b8b24ec2a2b9ff3d4d447f79bec846553f100 proof: 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 packageSequence:17684871 (00000000010dd987) height:110217401

differences

1-2 proofs

1: 76475d14e569bffc2e822e399eb0ec8c4d6b04d71c1340463250f12a2506d72b

2: 0ea04a867b36107e32a07707689376cb2048227b2c6393cddb473ab6d2c5e731

packageSequence

1: 17684857

2: 17684867

2-3 proofs

2: 0ea04a867b36107e32a07707689376cb2048227b2c6393cddb473ab6d2c5e731

3: a581750618671dbf00101dbc9bf2b481236d0718fe622d33b73eabe44b111dab

packageSequence

2: 17684867

3: 17684871

1-3 proofs

1: 76475d14e569bffc2e822e399eb0ec8c4d6b04d71c1340463250f12a2506d72b

3: a581750618671dbf00101dbc9bf2b481236d0718fe622d33b73eabe44b111dab

packageSequence

1: 17684857

3: 17684871

original tx

tendermint light client sync for height 110217401 by 0xb005741528b86f5952469d80a8614591e3c5b632 at block 3192 https://bscscan.com/tx/0x785c11458dd14a2a607ebd03cc6a64df28f34459d52cc0a4ce35329c152a899c

VERY FIRST CROSSCHAIN ACTIVITY

https://bscscan.com/tx/0x79575ff791606ef2c7d69f430d1fee1c25ef8d56275da94e6ac49c9c4cc5f433

payload: 0x0000000000000000000000000000000000000000000000000000038d7ea4c68000f86da0424e42000000000000000000000000000000000000000000000000000000000094000000000000000000000000000000000000000087b1a2bc2ec50000944e656459ed25bf986eea1196bc1b00665401645d94a10123c15a63135fe945a54232bae7fac8177056845fd12999

minting 0.05 BNB to Binance Deployer 1

proof: 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

height: 110217401 packageSequence: 2 channelId: 2