CVE-2023-37902 in Vyper
Summary
by MITRE • 07/26/2023
Vyper is a Pythonic programming language that targets the Ethereum Virtual Machine (EVM). Prior to version 0.3.10, the ecrecover precompile does not fill the output buffer if the signature does not verify. However, the ecrecover builtin will still return whatever is at memory location 0. This means that the if the compiler has been convinced to write to the 0 memory location with specially crafted data (generally, this can happen with a hashmap access or immutable read) just before the ecrecover, a signature check might pass on an invalid signature. Version 0.3.10 contains a patch for this issue.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 07/26/2023
The vulnerability described in CVE-2023-37902 affects the Vyper programming language, a Pythonic smart contract language designed for the Ethereum Virtual Machine. This issue represents a critical security flaw in how the ecrecover precompile function handles memory management during signature verification processes. The vulnerability specifically impacts versions prior to 0.3.10, where the implementation fails to properly initialize output buffers when signature validation fails. This behavioral inconsistency creates a potential attack vector that could allow malicious actors to bypass signature verification mechanisms through carefully crafted memory manipulation techniques.
The technical flaw manifests in the ecrecover precompile's improper handling of memory allocation when signature verification fails. When a signature verification fails, the precompile does not clear or properly fill the output buffer with zeros as expected. However, the ecrecover builtin function still returns whatever data happens to exist at memory location zero. This discrepancy becomes exploitable when the Vyper compiler places specially crafted data at memory location zero through operations such as hashmap access or immutable read operations. The vulnerability exploits the fact that memory location zero may contain arbitrary data from previous operations, allowing attackers to manipulate the return value of ecrecover to appear valid even when the underlying signature is invalid.
The operational impact of this vulnerability extends beyond simple signature bypassing to potentially compromise the integrity of Ethereum smart contracts that rely on cryptographic verification for security. Attackers can leverage this flaw to create valid-looking signatures that actually verify against invalid data, undermining the fundamental security assumptions of cryptographic verification in smart contracts. This issue affects any smart contract deployed using Vyper versions prior to 0.3.10 that utilize the ecrecover function for signature validation, potentially allowing unauthorized access to funds or critical contract functionality. The vulnerability is particularly concerning because it can be triggered through legitimate compiler operations, making it difficult to detect and prevent through standard code review processes.
The root cause of this vulnerability aligns with CWE-129, which addresses improper validation of array indices, and CWE-248, which covers exposure of an uninitialized variable. From an attack perspective, this vulnerability maps to techniques described in the MITRE ATT&CK framework under T1059.006 for execution through scripting and T1566 for social engineering via software supply chain compromises. The patch implemented in Vyper version 0.3.10 addresses this issue by ensuring proper memory initialization and buffer handling during ecrecover operations. Organizations should immediately upgrade to version 0.3.10 or later to mitigate this vulnerability, while also conducting thorough code audits to identify any smart contracts that may be susceptible to similar memory manipulation attacks. The vulnerability serves as a reminder of the critical importance of proper memory management in smart contract development environments where cryptographic operations are fundamental to security.