How to Find Bugs in CosmWasm Smart Contract?

Doyeon Kim (LINE Plus / Security R&D / Security Researcher)

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Transcript

2. Who am I? › Experience › Security Research Engineer, LINE › Main Works › Security Research › Security Consulting › Research Interests › Computer Software Security › Fuzz Testing › Smart Contract Security
3. Conclusion Design How Bugs Can Occur? Challenges Introduction Agenda And…
4. Introduction › Blockchain is thought as a distributed computing system. › Smart contract is a collection of code and data executed on blockchain. $ Blockchain $ </> Digital Cash </> Smart Contract Smart Contract
5. Introduction › There are several blockchain businesses in LINE. › Examples: BITFRONT, LINE BITMAX, LINK, LINE NFT …
6. Introduction › There are several blockchain businesses in LINE. › Examples: BITFRONT, LINE BITMAX, LINK, LINE NFT … › LINE uses CosmWasm smart contract written in Rust.
7. Introduction › There are several blockchain businesses in LINE. › Examples: BITFRONT, LINE BITMAX, LINK, LINE NFT … › LINE uses CosmWasm smart contract written in Rust. › CosmWasm is a smart contracting platform built for the Cosmos ecosystem[1]. › Cosmos is an ecosystem of blockchains that can scale and interoperate with each other[2]. [1] https://docs.cosmwasm.com/docs/1.0/ [2] https://v1.cosmos.network/intro
8. Introduction › There are several blockchain businesses in LINE. › Examples: BITFRONT, LINE BITMAX, LINK, LINE NFT … › LINE uses CosmWasm smart contract written in Rust. › CosmWasm is a smart contracting platform built for the Cosmos ecosystem[1]. › Cosmos is an ecosystem of blockchains that can scale and interoperate with each other[2]. › CosmWasm smart contract runs the WebAssembly virtual machine. cf. Ethereum smart contract [1] https://docs.cosmwasm.com/docs/1.0/ [2] https://v1.cosmos.network/intro
9. Introduction › Cosmos ecosystem is one of the popular blockchains which support a smart contract. › It takes 4th place as a result of sorting by market cap which is about $4,000,159,801. (2022.10.31) Reference: https://cryptoslate.com/cryptos/smart-contracts/
10. Introduction › Bugs in smart contract can cause a catastrophic loss of digital assets. › Examples: Ethereum, Solana, Juno, … $5M Ethereum Solana Juno $70M $36M [1] https://www.coindesk.com/markets/2022/08/03/phantom-wallet-exploit-drains-millions-in-sol-tokens/ [2] https://www.coindesk.com/learn/2016/06/25/understanding-the-dao-attack/ [3] https://www.coindesk.com/tech/2022/05/05/typo-moves-36m-in-seized-juno-tokens-to-wrong-wallet/
11. Introduction › There are a lot of tools for finding vulnerabilities in Ethereum smart contracts. › One of the state-of-the-art tools is Smartian[1][2] which is a grey-box concolic fuzzer for finding bugs in Ethereum smart contracts using static and dynamic data-flow analysis. › The result said data-flow analyses are important to find bugs in smart contracts. [1] J.Choi, D.Kim, S.Kim, G.Grieco, A.Groce, and S.K.Cha, “Smartian: Enhancing smart contract fuzzing with static and dynamic data-flow analyses,” in Proceedings of the 36th IEEE/ACM Internatiional Conference on Automated Software Engineering (ASE), 2021. [2] https://github.com/SoftSec-KAIST/Smartian
12. Introduction Persistent State User </> Smart Contract
13. Introduction Persistent State g(uint y) { ... = state + 1; ... } f(uint x) { state = ...; ... } User </> Smart Contract › Smart contract defines functions that a user can call.
14. Introduction Persistent State g(uint y) { ... = state + 1; ... } f(uint x) { state = ...; ... } State variable (persistent) User </> state Smart Contract › Smart contract defines functions that a user can call. › Each function can read or write persistent state variables.
15. Introduction Persistent State g(uint y) { ... = state + 1; ... } f(uint x) { state = ...; ... } Call State variable (persistent) User </> state Smart Contract › Smart contract defines functions that a user can call. › Each function can read or write persistent state variables.
16. Introduction › The number of studies and projects about the security of CosmWasm smart contract is low. › Google Scholar: 44,000 vs 17
17. Introduction › The number of studies and projects about the security of CosmWasm smart contract is low. › Google Scholar: 44,000 vs 17 › GitHub: 161 vs 0
18. Introduction Summary › Recently, several bugs in the CosmWasm smart contracts are discovered. › It’s important to find such bugs in the CosmWasm smart contracts as we expect the use of them to increase. › However, there is no open-sourced tool in order to find bugs in the CosmWasm smart contracts. Need to Make Testing Tool!
20. Rust is Safer than Solidity!
21. How Bugs Can Occur? Outdated Vulnerable Module Used › Using a vulnerable module can be problematic especially if there are publicly discovered bugs and issues that affect the current module.
22. How Bugs Can Occur? Outdated Vulnerable Module Used › Using a vulnerable module can be problematic especially if there are publicly discovered bugs and issues that affect the current module. Reference: https://github.com/CosmWasm/cosmwasm/commit/c1edd61a96f57072cb8675734c91649c40751a85
23. How Bugs Can Occur? Outdated Vulnerable Module Used › Using a vulnerable module can be problematic especially if there are publicly discovered bugs and issues that affect the current module. Reference: https://github.com/CosmWasm/cosmwasm/commit/c1edd61a96f57072cb8675734c91649c40751a85
24. How Bugs Can Occur? Address Bypass › A smart contract might wish to only access certain addresses, or not to access certain addresses. › If there is a problem in address check, a smart contract can allow unwanted addresses to access it. › ex: An attacker can receive all money in a smart contract.
25. How Bugs Can Occur? Address Bypass › A smart contract might wish to only access certain addresses, or not to access certain addresses. › If there is a problem in address check, a smart contract can allow unwanted addresses to access it. › ex: An attacker can receive all money in a smart contract. › For example, using previous vulnerability, if there is a blocklist that all addresses are lowercase, the use of an uppercase address can bypass the blocklist. User </> Smart Contract Source code Blocklist - user - … “User” and “user” are same person ! Can Access
26. How Bugs Can Occur? Integer-Related Bugs › When integer overflow or underflow occurs, a panic!() occur. › In the case of Ethereum smart contract, when integer overflow/underflow occurs, the value is also overflowed/underflowed without error.
27. How Bugs Can Occur? Integer-Related Bugs › When integer overflow or underflow occurs, a panic!() occur. › In the case of Ethereum smart contract, when integer overflow/underflow occurs, the value is also overflowed/underflowed without error. › When you try integer type conversion using into() or try_into(), type conversion error can occur.
28. How Bugs Can Occur? Integer-Related Bugs › When integer overflow or underflow occurs, a panic!() occur. › In the case of Ethereum smart contract, when integer overflow/underflow occurs, the value is also overflowed/underflowed without error. › When you try integer type conversion using into() or try_into(), type conversion error can occur. Reference: https://github.com/LoTerra/loterra-staking-contract/blob/main/src/math.rs u128 u256
29. Fuzz Testing (Fuzzing) › Repeatedly execute the target program with random inputs. › Simple but effective technique to find vulnerabilities. › Employed by major software companies (e.g., Google and Microsoft) Inputs Program Crash Mutate
30. Challenges
31. Challenges › There is no open-sourced bug-finder for CosmWasm smart contract.
32. Challenges › There is no open-sourced bug-finder for CosmWasm smart contract. › There is no tool to instrument the data-flow for CosmWasm smart contract as far as we know. › Tracking data-flow for state is important to bugs in smart contracts[1]. [1] J.Choi, D.Kim, S.Kim, G.Grieco, A.Groce, and S.K.Cha, “Smartian: Enhancing smart contract fuzzing with static and dynamic data-flow analyses,” in Proceedings of the 36th IEEE/ACM Internatiional Conference on Automated Software Engineering (ASE), 2021.
33. Challenges › There is no open-sourced bug-finder for CosmWasm smart contract. › There is no tool to instrument the data-flow for CosmWasm smart contract as far as we know. › Tracking data-flow for state is important to bugs in smart contracts[1]. › We should do black-box fuzzing. › How can we do efficiently? [1] J.Choi, D.Kim, S.Kim, G.Grieco, A.Groce, and S.K.Cha, “Smartian: Enhancing smart contract fuzzing with static and dynamic data-flow analyses,” in Proceedings of the 36th IEEE/ACM Internatiional Conference on Automated Software Engineering (ASE), 2021. Inputs </> Smart Contract ?
34. Challenges Pseudo Code Example STATE.x = 0, STATE.y = 0, STATE.z = 0 def SetX(value): STATE.x = value + 102 def SetY(): STATE.y = STATE.x + 13 def Foo(value): STATE.z = STATE.y if 200 < STATE.z < value: // bug else: // Safe
35. Challenges Pseudo Code Example STATE.x = 0, STATE.y = 0, STATE.z = 0 def SetX(value): STATE.x = value + 102 def SetY(): STATE.y = STATE.x + 13 def Foo(value): STATE.z = STATE.y if 200 < STATE.z < value: // bug else: // Safe SetX(110) Foo(300) SetY()
36. Challenges Pseudo Code Example STATE.x = 0, STATE.y = 0, STATE.z = 0 def SetX(value): STATE.x = value + 102 def SetY(): STATE.y = STATE.x + 13 def Foo(value): STATE.z = STATE.y if 200 < STATE.z < value: // bug else: // Safe SetX(110) Foo(300) SetY() STATE.x = STATE.y = STATE.z = 0 0 0 212 225 225
37. Challenges › Find the sequence of messages that change the state. › Case of pseudo code in previous slide: › SetX(value) › SetX(value) -> SetY() › SetX(value) -> SetY() -> Foo(value) › Try fuzzing more by marking the sequence of messages that change the state.
38. Design Schema Bugs Architecture </> state Smart Contract Schema Parsing Fuzzing Schema Result
39. Design Compilation Schema </> Smart Contract Source code 0101.. Smart Contract Bytecode › When a source code of smart contract is compiled, bytecode and schema are generated. Compile...
40. Design Compilation Schema </> Smart Contract Source code { “contract_name”: …, …, “instantiate”: { … }, “execute”: { … }, “query”: { … }, … “responses”: { … }, } 0101.. Smart Contract Bytecode › When a source code of smart contract is compiled, bytecode and schema are generated. › A schema file includes type of each function and type of each parameter of function. Compile...
41. Design Schema Bugs Architecture </> state Smart Contract Schema Parsing Fuzzing Schema Result
42. Design Schema Parsing › Parsing “definitions” is necessary in which additional type information is stored. “amount”: { “$ref”: “#/definitions/Coin” }, “definitions”: { “Coin”: { “amount”: { “$ref”: “#/definitions/Uint128” }, “denom”: { “type”: “string” }, }, “Uint128”: { “type”: “string” }, … }
43. Design Schema Parsing › Parsing “definitions” is necessary in which additional type information is stored. › In some cases, we need to refer to the other type stored in “definitions” for getting an exact type. Uint128 Coin amount “amount”: { “$ref”: “#/definitions/Coin” }, “definitions”: { “Coin”: { “amount”: { “$ref”: “#/definitions/Uint128” }, “denom”: { “type”: “string” }, }, “Uint128”: { “type”: “string” }, … }
44. Design Schema Parsing › Parsing “definitions” is necessary in which additional type information is stored. › In some cases, we need to refer to the other type stored in “definitions” for getting an exact type. › We use topological sort to determine which type to parse first. Uint128 Coin amount “amount”: { “$ref”: “#/definitions/Coin” }, “definitions”: { “Coin”: { “amount”: { “$ref”: “#/definitions/Uint128” }, “denom”: { “type”: “string” }, }, “Uint128”: { “type”: “string” }, … }
45. Design Schema Bugs Architecture </> state Smart Contract Schema Parsing Fuzzing Schema Result
46. Design Fuzzing Fuzzing Seed 1 Bugs … Seed 2 Seed N Worker 1 Worker 2 Worker N Context 1 Context 2 Context N › Our fuzzer works in parallel mode as default. › The sequence of transactions which is a seed are executed on one worker. › The result is stored in shared memory. STATE.x = 30 STATE.x = 10 … value = STATE.x // 10
47. Design Fuzzing › For discovering the flow of persistent state variable indirectly, we send two query messages per transaction: One is before the transaction and the other is after the transaction. › We can find out which persistent state is updated in the transaction.
48. Design Fuzzing › For discovering the flow of persistent state variable indirectly, we send two query messages per transaction: One is before the transaction and the other is after the transaction. › We can find out which persistent state is updated in the transaction. Transaction 1 Transaction 3 Transaction 2 Query 0 Query 1 Query 2 We can know initialized state. Find out updated states.
49. Design Pseudo Code Example STATE.x = 0, STATE.y = 0, STATE.z = 0 def SetX(value): STATE.x = value + 102 def SetY(): STATE.y = STATE.x + 13 def Foo(value): STATE.z = STATE.y if 200 < STATE.z < value: // bug else: // Safe
50. Design Pseudo Code Example STATE.x = 0, STATE.y = 0, STATE.z = 0 def SetX(value): STATE.x = value + 102 def SetY(): STATE.y = STATE.x + 13 def Foo(value): STATE.z = STATE.y if 200 < STATE.z < value: // bug else: // Safe SetX(110) Foo(300) SetY() STATE.x = 212 STATE.y = 0 STATE.z = 0 STATE.x = 212 STATE.y = 225 STATE.z = 0 STATE.x = 212 STATE.y = 225 STATE.z = 225
51. Design Bug Oracle › We basically detect a runtime error which occurs during execution time. › Gas depletion due to lack of gas. › Panic including assertion failure, integer overflow. › Out of bound error when accessing an array that exceeds its size. › … › We currently support to detect only runtime errors.
52. Instrumentation What’s Next?
53. What’s Next? Schema Bugs Instrumentation </> state Smart Contract Schema Parsing Fuzzing Executor
54. More Bug Oracles… Instrumentation What’s Next?
55. What’s Next? Schema Bugs More Bug Oracles… </> state Smart Contract Schema Parsing Fuzzing Bug Oracles
56. More Bug Oracles… Handling various kinds of messages Instrumentation What’s Next?
57. What’s Next? Schema Bugs Handling Various Kind of Messages </> state Smart Contract Schema Parsing Fuzzing Message Executor
58. Static Analysis More Bug Oracles… Handling various kinds of messages Instrumentation What’s Next?
59. What’s Next? Schema Bugs Static Analysis </> state Smart Contract Schema Parsing Fuzzing Static Analysis
60. Static Analysis More Bug Oracles… And… Handling various kinds of messages Instrumentation What’s Next?
61. Let’s Develop Together! Coming Soon…
62. #ContactInfo E-mail: doyeon1017@linecorp.com GitHub: kimdora
63. Thank you!