CoW Swap is the first trading interface built on top of CoW Protocol. CoW Swap is a Meta DEX aggregator that allows you to buy and sell tokens using gasless orders that are settled peer-to-peer among users, or into any on-chain liquidity source while providing protection from MEV.
Cow Protocol engaged Ackee Blockchain to perform a security review of the ComposableCoW & ExtensibleFallbackHandler with a total time donation of 8 engineering days in a period between July 18 and July 28, 2023.
METHODOLOGY
We began our review by using static analysis tools, namely Wake. We then took a deep dive into the logic of the contracts. For testing, we have involved Wake testing framework. During the review, we paid special attention to:
- replay attacks
- signature validation
- payload manipulation
- detecting possible reentrancies
- ensuring the arithmetic of the system is correct
- the correctness of encoding/decoding data
- ERC-1271 compliance
- looking for common issues such as data validation.
SCOPE
The audit has been performed on the following scope:
- https://github.com/rndlabs/composable-cow
- Commit cd893fa
- All contracts
- https://github.com/rndlabs/safe-contracts
- Commite53ffea
- contracts/handler/ExtensibleFallbackHandler.sol
- All contracts in contracts/handler/extensible/
The review was done on the given commits Revision 1.0:
- 27ec79b for ComposableCow
- 11273c1 for ExtensibleFallbackHandler
Revision 1.2 was done on the ComposableCow commit bd2634d, the ExtensibleFallbackHandler commit was not changed since Revision 1.1.
FINDINGS
Here we present our findings.
Critical severity
C1: StopLoss arithmetic mismatches
High severity
No high severity issues were found.
Medium severity
M1: Oracle data validation
Low severity
L1: Constructor data validation
Warning severity
W1: GPv2Order data tampering
W2: Revert conditions inconsistency
W3: Vulnerable MerkleProof library
W4: GoodAfterTime order is missing the receiver address
Informational severity
I1: Unnecessary SafeMath
I2: Missing cabinet cleanup
I3: Errors in the documentation
I4: TradeAboveThreshold order receiver naming
I5: Inconsistent error
I6: Commented-out code
I7: Inconsistent naming
CONCLUSION
Our review resulted in 14 findings, ranging from Informational to Critical severity. The critical issue C1: StopLoss arithmetic mismatches has been fixed according to our recommendations, and the decimals handling in the M1: Oracle data validation issue were implemented properly (Revision 1.2).
Other issues are low-severity data validations, warnings and informational findings, which are recommendations rather than issues. The overall code quality and architecture are professional. The whole project is well documented and contains in-code NatSpec documentation and detailed comments.
Ackee Blockchain recommendes CoW Protocol:
- to add oracle data validations
- to be aware of zero-address validations
- to unify syntax and naming
- to address all reported issues.
As of Revision 1.2, L1: Constructor data validation issue was acknowledged, all other issues were fixed.
Ackee Blockchain’s full COW Protocol audit report with a more detailed description of all findings and recommendations can be found here.
We were delighted to audit Cow Protocol and look forward to working with them again.
