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1Inch Audit – LimitOrder Protocol


CoinFabrik was asked to audit the Limit Order Protocol contracts for 1inch. Limit orders are contracts between a maker, who generates the order, and a taker, who accepts the order. A maker defines an order (offchain) including a pair of tokens, an exchange rate and a total amount which he wants to exchange–among other parameters. A taker who accepts this order can fill the order and have it executed, if certain conditions hold.

We have audited the contracts. a summary of our discoveries, what is their current status, and then we will show the details of our findings.


We analyzed the contracts received from the private github repository: 1inch/limit-order-protocol (

This audit is based on the following commit: fc528b390bad66927b9316470e4c86d06df58563


The audited contracts are:

  • contracts/LimitOrderProtocol.sol: main functions
  • contracts/helpers/AmountCalculator.sol: helper functions calculating maker and taker amounts
  • contracts/helpers/PredicateHelper.sol: helper functions for building predicates
  • contracts/helpers/ImmutableOwner.sol: modifier
  • contracts/helpers/ERC20Proxy.sol: proxy helper
  • contracts/helpers/ERC1155Proxy.sol: proxy helper
  • contracts/helpers/ERC721Proxy.sol: proxy helper
  • contracts/helpers/NonceManager.sol: nonces
  • contracts/libraries/ArgumentsDecoder.sol: help decoding arguments
  • contracts/libraries/UncheckedAddress.sol: includes calls to (external) token functions
  • contracts/interfaces/IEIP1271.sol: interface
  • contracts/interfaces/InteractiveMaker.sol: interface


The following analyses were performed:

  • Misuse of the different call methods
  • Integer overflow errors
  • Division by zero errors
  • Outdated version of Solidity compiler
  • Front running attacks
  • Reentrancy attacks
  • Misuse of block timestamps
  • Softlock denial of service attacks
  • Functions with excessive gas cost
  • Missing or misused function qualifiers
  • Needlessly complex code and contract interactions
  • Poor or nonexistent error handling
  • Failure to use a withdrawal pattern
  • Insufficient validation of the input parameters
  • Incorrect handling of cryptographic signatures

Specific Analyses for this Project

We further tested design flaws allowing makers/takers to take advantage of each other. This includes the following analyses:

  1. We tested whether takers could fill orders with malicious parameters,   allowing them to take advantage of makers, e.g., with an improved takingAmount / makingAmount ratio.
  2. We tested border conditions by adapting the supplied truffle tests to include security-relevant scenarios.
  3. Finally, since the contract makes calls to external contracts from parameters, we looked for vulnerabilities arising from these calls.

Findings and Fixes

ID Title Severity Status
CR-1 Front-running attack in malicious order leads to arbitrary rate set by maker Critical Fixed
EN-1 Use of deprecated functions Enhancement Not fixed

Severity Classification

Security risks are classified as follows:

  • Critical: These are issues that we manage to exploit. They compromise the system seriously. They must be fixed immediately.
  • Medium: These are potentially exploitable issues. Even though we did not manage to exploit them or their impact is not clear, they might represent a security risk in the near future. We suggest fixing them as soon as possible.
  • Minor: These issues represent problems that are relatively small or difficult to take advantage of but can be exploited in combination with other issues. These kinds of issues do not block deployments in production environments. They should be taken into account and be fixed when possible.
  • Enhancement: These kinds of findings do not represent a security risk. They are best practices that we suggest to implement.

This classification is summarized in the following table:

Critical Yes Yes Immediately
Medium In the near future Yes As soon as possible
Minor Unlikely No Eventually
Enhancement No No Eventually

Issues Found by Severity

Critical Severity

CR-01 Front-running attack in malicious order leads to arbitrary rate setting by maker (fixed)

The LimitOrder contract allows a maker to define orders where a makingAmount, a takingAmount, getMakerAmount and getTakerAmount parameters are set (among others). When fillOrder is called by a taker, the makingAmount and takingAmount values of the exchange are computed on the fly, and may use these  getMakerAmount and getTakerAmount functions defined by the maker arbitrarily.

A malicious maker could create an order setting custom getMakerAmount and getTakerAmount functions on an arbitrary maker-controlled contract together with a different makingAmount/takingAmount price. The maker’s contract could be  implemented so that if the taker evaluates these getMakerAmount and getTakerAmount, he obtains the original makingAmount and takingAmount values of the order. However, when the taker calls fillOrder() with makingAmount set to 0, the maker may execute a front-running attack calling a setter in the maker’s malicious contract which changes the value returned by getMakerAmount. Hence, when fillOrder is executed, it will use the new value which may be lower than the value expected by the taker (makingAmount). (Respectively with takingAmount=0 and getTakerAmount.)


The expected behavior of fillOrder should be documented and in particular, what is the intended use of thresholdAmount, getMakerAmount and getTakerAmount, so that parties are fully aware of the possible order execution outcomes.

Follow up

1inch implemented a solution which eliminates the threat by adding a parameter, thresholdAmount, to fillOrder with which the taker stops any attack.

Before placing the transfers, the code in fillOrder requires that

takingAmount <= thresholdAmount

when takingAmount is determined by getMakerAmount, and it requires that

makingAmount >= thresholdAmount

when makingAmount is determined by getMakerAmount.

The solution thus eliminates the threat in the case where the taker enters thresholdAmount according to his needs: for example, a taker which sets a nonzero makingAmount value in fillOrder may specify the thresholdAmount to be equal to the takingAmount he expects to receive (so that the maker cannot make the order’s takingAmount any bigger); respectively, the taker entering a takingAmount value in the fillOrder may specify the thresholdAmount to be equal to the expected makingAmount (so that the maker cannot make the order’s makingAmount any smaller). When the thresholdAmount values differ from what the taker expects to receive, this may prevent the transaction from happening or may allow the maker to take an advantage.

An alternative solution, proposed and discarded by 1inch, includes a different additional parameter, minPrice, to be added to fillOrder and the contract requires that

makingAmount * 1e18 / takingAmount >= minPrice.

This solution is analogous to the thresholdAmount solution. Generally speaking, a taker may perceive problematic paying a price below the one entered when calling fillOrder(); he may even dismiss thresholdAmount (or minPrice) as he expects the order to be executed according to what he inputs without going into the additional steps.

Medium Severity

No issues found.

Minor Severity

No issues found.


EN-01 Use of deprecated functions

The functions remaining() and fillOrder() make use of value1.sub(value2, error_message) which is deprecated (see link).


Use trySub() instead.


We found the contracts to be concise with scarce documentation. The code reduces to a single contract. Tests and testing scripts included in the repository were helpful to understand the limit order execution flow, and also in evaluating certain scenarios. We included in our analysis checks to design flaws specific to this model.

A critical issue was discovered by 1inch that allows a malicious maker to deceive takers in receiving a lower-than-expected exchange rate. The issue was fixed by providing the taker with a security parameter which ensures that attacks are not possible when the parameter is chosen respecting his expectations.

Disclaimer: This audit report is not a security warranty, investment advice, or an approval of the 1Inch project since CoinFabrik has not reviewed its platform. Moreover, it does not provide a smart contract code faultlessness guarantee.