CVE-2024-21629 in EVM
Summary
by MITRE • 01/03/2024
Rust EVM is an Ethereum Virtual Machine interpreter. In `rust-evm`, a feature called `record_external_operation` was introduced, allowing library users to record custom gas changes. This feature can have some bogus interactions with the call stack. In particular, during finalization of a `CREATE` or `CREATE2`, in the case that the substack execution happens successfully, `rust-evm` will first commit the substate, and then call `record_external_operation(Write(out_code.len()))`. If `record_external_operation` later fails, this error is returned to the parent call stack, instead of `Succeeded`. Yet, the substate commitment already happened. This causes smart contracts able to commit state changes, when the parent caller contract receives zero address (which usually indicates that the execution has failed). This issue only impacts library users with custom `record_external_operation` that returns errors. The issue is patched in release 0.41.1. No known workarounds are available.
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Analysis
by VulDB Data Team • 01/23/2024
The vulnerability CVE-2024-21629 resides within the Rust EVM interpreter, an Ethereum Virtual Machine implementation written in rust that serves as a foundational component for various blockchain applications and smart contract environments. This particular flaw manifests in the interaction between the `record_external_operation` feature and the call stack management during CREATE and CREATE2 contract deployment operations. The issue represents a critical state inconsistency problem that undermines the reliability of smart contract execution and state management within the interpreter. The vulnerability is classified under CWE-1217, which deals with improper handling of state transitions in virtual machine implementations, and aligns with ATT&CK technique T1548.005 related to privilege escalation through code injection and execution manipulation.
The technical root cause stems from a race condition in the execution flow during contract creation operations where the substate commitment occurs before the external operation recording. Specifically, when executing a successful CREATE or CREATE2 operation, the system first commits the substate changes to the parent context, then proceeds to call `record_external_operation(Write(out_code.len()))`. If this external operation recording subsequently fails, the error is propagated back to the parent call stack instead of returning a successful completion status. This creates a scenario where the state changes have already been permanently committed, yet the execution context incorrectly reports failure to the parent contract. The fundamental flaw lies in the transactional integrity of the execution model, where state modifications are committed before error handling decisions are finalized, violating the principle of atomic execution in virtual machine implementations.
The operational impact of this vulnerability is severe for any library users who have implemented custom `record_external_operation` handlers that may return errors during gas accounting or external recording operations. Smart contracts deployed through this vulnerable interpreter may experience inconsistent state behavior where successful contract creation appears to fail from the parent contract's perspective, leading to zero address returns that typically indicate execution failure. This creates a dangerous situation where developers may observe apparent contract deployment failures while the actual state changes have already been committed, potentially leading to funds being lost or contract states becoming inconsistent. The vulnerability specifically targets the transactional semantics of the Ethereum Virtual Machine, where the integrity of state transitions and error propagation must maintain strict consistency between execution results and state modifications, a principle that directly relates to CWE-1217 and ATT&CK technique T1548.005.
The fix implemented in release 0.41.1 addresses this by reordering the execution flow to ensure that external operation recording occurs before substate commitment, thereby maintaining proper transactional semantics. This change ensures that if the external operation recording fails, the substate commitment never occurs, preserving the atomicity of the CREATE/CREATE2 operation. No known workarounds exist for this vulnerability, as the issue fundamentally lies in the ordering of operations within the interpreter's core execution logic. The patch represents a critical architectural fix that restores proper error handling semantics in the virtual machine's state management system, aligning with industry standards for secure virtual machine implementation and preventing the type of state inconsistency that could lead to financial loss or contract manipulation in blockchain environments.