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code-423n4 / 2021-08-gravitybridge-findings

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Direct usage of `ecrecover` allows signature malleability #61

Open code423n4 opened 3 years ago

code423n4 commented 3 years ago

Handle

shw

Vulnerability details

Impact

The verifySig function of Gravity calls the Solidity ecrecover function directly to verify the given signatures. However, the ecrecover EVM opcode allows malleable (non-unique) signatures and thus is susceptible to replay attacks.

Although a replay attack seems not possible here since the nonce is increased each time, ensuring the signatures are not malleable is considered a best practice (and so is checking _signer != address(0), where address(0) means an invalid signature).

Proof of Concept

Referenced code: Gravity.sol#L153

SWC-117: Signature Malleability SWC-121: Missing Protection against Signature Replay Attacks

Recommended Mitigation Steps

Use the recover function from OpenZeppelin's ECDSA library for signature verification.

jkilpatr commented 3 years ago

Best practicies advice may belong in category zero. But in general I agree with the advice here and that this is valid feedback despite lacking a specific attack vector.

semi-duplicate of #43, #28 which mention the validation issue. #22 also mentions malleability.

albertchon commented 3 years ago

Marking https://github.com/code-423n4/2021-08-gravitybridge-findings/issues/61 as primary for the signature malleability issue.

Duplicates:

loudoguno commented 3 years ago

reopening as per judges assessment as "primary issue" on findings sheet