CVE-2025-27104 is a vulnerability affecting the vyper, a Pythonic Smart Contract Language for the EVM. This vulnerability allows multiple evaluation of a single expression in the iterator target of a for loop. While the iterator expression cannot produce multiple writes, it can consume side effects produced in the loop body (e.g., read a storage variable updated in the loop body) and thus lead to unexpected program behavior.
The issue specifically concerns reads in iterators which contain an if expression (e.g., `for s: uint256 in ([read(), read()] if True else [])`). This can cause interleaving of reads with writes in the loop body, creating potential inconsistencies. Vyper for loops allow two kinds of iterator targets, namely the `range()` builtin and an iterable type like SArray and DArray.
During code generation, iterable lists are required not to produce any side effects. However, this does not prevent the iterator from consuming side effects provided by the body of the loop. This issue is expected to be addressed in version 0.4.1, and users should prioritize upgrading as soon as the patched release is available.
Currently, there are no known workarounds for this vulnerability, making the urgency for remediation critical.
Vulnerability Details
The CVE-2025-27104 vulnerability is classified under CWE-662 and has a CVSS score of 2.3, indicating a low severity level. The vulnerability affects all versions of vyper prior to version 0.4.1.
Technical Analysis
The root cause of this vulnerability stems from how the vyper language processes for loop iterators. The iterator can read variables that may have been modified in the loop body, leading to unexpected behaviors. Since the attack vector is classified as NETWORK, and the attack complexity is low, a successful exploit could be achieved with minimal effort.
Risk & Impact Analysis
Risk to organizations includes potential disruption of smart contract executions, leading to integrity issues within blockchain applications. Given the nature of the vulnerability, the blast radius could be significant, depending on the deployment of vyper in various applications.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The vulnerability affects all versions of vyper prior to 0.4.1. Organizations using this version should plan for immediate updates.
Mitigation & Remediation
Organizations should prioritize upgrading to vyper version 0.4.1 or later as soon as it becomes available. If immediate upgrades are not feasible, users should consider implementing strict code reviews to identify potential vulnerabilities in smart contracts.
Detection Guidance
Developers should monitor for unusual behavior in smart contracts that utilize vyper, particularly in contexts where for loops are used. Logging read operations and variable state changes can provide insights into potential vulnerabilities.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2025-27104 highlights the ongoing need for robust testing and validation of smart contracts. This vulnerability reflects a pattern of potential side effects in programming languages that handle smart contracts, emphasizing the importance of thorough testing.
Security teams should take this opportunity to review their development and deployment practices, focusing on the potential risks introduced by programming languages like vyper. Organizations should be proactive in their approach to vulnerability management.
For more insights on security practices, consider exploring our vulnerability management program and incorporate lessons learned into your organization's security posture.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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