Analysis of Solidity Compiler Vulnerabilities and Countermeasures

The compiler is one of the fundamental components of modern computer systems, and its function is to convert high-level programming language source code into executable instruction code for computers. Although developers and security personnel typically focus on the security of application code, the compiler itself, as a computer program, may also have security vulnerabilities, which can pose serious security risks in certain situations.

The role of the Solidity compiler is to convert smart contract code into Ethereum Virtual Machine ( EVM ) bytecode. Unlike vulnerabilities in the EVM itself, vulnerabilities in the Solidity compiler primarily manifest during the conversion of Solidity to EVM bytecode, which does not directly affect the Ethereum network itself, but may lead to discrepancies between the generated EVM bytecode and the developers' expectations.

Here are some real examples of Solidity compiler vulnerabilities:

1. SOL-2016-9 HighOrderByteCleanStorage: The vulnerability exists in early versions of the Solidity compiler ( >=0.1.6 <0.4.4). Because the compiler did not properly clear the high bits when handling integer overflow, it may lead to adjacent variables being unexpectedly modified.

2. SOL-2022-4 InlineAssemblyMemorySideEffects: The vulnerability exists in compiler versions 0.8.13 to 0.8.15. Due to compiler optimizations analyzing individual assembly blocks, it may incorrectly remove seemingly redundant but actually useful memory write instructions.

3. SOL-2022-6 AbiReencodingHeadOverflowWithStaticArrayCleanup: The vulnerability affects compiler versions from 0.5.8 to 0.8.16. During the abi.encode operation on calldata type arrays, certain data was incorrectly cleared, leading to adjacent data being modified.

In response to the Solidity compiler vulnerability, the Cobo blockchain security team recommends the following:

For Developers:

• Use a newer version of the Solidity compiler
• Improve unit test cases
• Avoid using inline assembly, complex ABI encoding and decoding operations.

To security personnel:

• Consider the security risks that compilers may introduce during audits.
• Urge to upgrade the compiler version during the development process.
• Assess the actual security impact of compiler vulnerabilities based on specific circumstances.

Some practical resources:

• Solidity Official Security Alert
• Bug list in the Solidity GitHub repository
• Bug list for each version of the compiler
• Security Tips on Etherscan Contract Code Page

In summary, developers and security personnel should pay attention to the security risks that may arise from vulnerabilities in the Solidity compiler, and take measures such as upgrading the compiler and improving testing to reduce related risks.