Biconomy: Nexus

The [K1Validator::isValidSignatureWithSender](https://github.com/Cyfrin/2024-07-biconomy/blob/9590f25cd63f7ad2c54feb618036984774f3879d/contracts/modules/validators/K1Validator.sol#L99) function is vulnerable to signature malleability. This allows an attacker to create multiple valid signatures for the same message, potentially bypassing restrictions that rely on unique signatures.

​

The `isValidSignatureWithSender` function is affected by a signature malleability issue. The root cause of this vulnerability lies in the [SignatureCheckerLib](https://github.com/Vectorized/solady/blob/a34977e56cc1437b7ac07e6356261d2b303da686/src/utils/SignatureCheckerLib.sol#L23) used within the function, which does not check if a signature is non-malleable.

function isValidSignatureWithSender(address, bytes32 hash, bytes calldata data) external view returns (bytes4) {

​

-> if (SignatureCheckerLib.isValidSignatureNowCalldata(owner, hash, data)) {

-> if (SignatureCheckerLib.isValidSignatureNowCalldata(owner, MessageHashUtils.toEthSignedMessageHash(hash), data)) {

As a result, an attacker can create multiple valid signatures for the same message (digest). This allows the attacker to bypass restrictions that rely on the uniqueness of signatures, potentially leading to unauthorized actions or replay attacks.

​

This vulnerability poses a significant security risk as it allows the creation of multiple valid signatures for the same message. Consequently, an attacker can bypass restrictions that rely on the uniqueness of signatures. This could potentially lead to unauthorized actions or replay attacks, undermining the integrity and security of the contract.

​

[Similar Finding](https://solodit.xyz/issues/m-9-signature-is-malleable-sherlock-titles-publishing-protocol-git).

​

Manual review

​

Implement EIP-712 for typed data signing, which includes nonce and domain separation to prevent replay attacks.

​

Ensure the signature scheme used checks for non-malleability.