Overview

CVE-2026-114663 is a significant vulnerability affecting Vyper, a language used for writing smart contracts on the Ethereum blockchain. The vulnerability has a CVSS score of 8.4, indicating high severity. It exists in Vyper versions 0.4.0b1 through 0.5.0b1 and is caused by the miscompilation of certain constants and default arguments from imported modules. This miscompilation can allow attackers to influence input values, potentially leading to the corruption of validation or accounting logic within smart contracts.

Understanding the Vulnerability / Threat

Root Cause Analysis

The root cause of CVE-2026-114663 is a design issue within the Vyper compiler. Specifically, the parse_Name function resolves names in the using function's scope rather than at declaration. This leads to a situation where a contract's parameter, local, or loop variable can share a name with an imported module's constant or default argument, allowing attacker-influenced input to replace intended values. This vulnerability falls under CWE-706, which relates to Use of Incorrectly-Resolved Name.

Attack Surface & Vector

The attack surface for this vulnerability is local, meaning an attacker needs to have local access to exploit it. The attack complexity is low, and no privileges are required. The vulnerability affects the confidentiality, integrity, and availability of the system, all with a high impact. The attack vector is AV:L, indicating a local attack vector, with AC:L for low attack complexity, and PR:N meaning no privileges are required.

Exploitation Mechanics — Scenario Walkthrough

Scenario: Compromising a Smart Contract through Vyper Compiler Vulnerability

Initial Position: An attacker has local access to a system where a Vyper smart contract is being compiled and deployed on the Ethereum blockchain.

Triggering the Flaw: The attacker crafts a smart contract that imports a module with a constant or default argument that can be miscompiled by Vyper versions 0.4.0b1 through 0.5.0b1. The attacker influences the input to replace an intended value with an out-of-range value for a narrow type, such as uint8.

What Breaks: The miscompilation allows the attacker's input to corrupt validation or accounting logic within the smart contract. This could happen when the contract's parameter or local variable inadvertently shadows an imported constant or default argument, leading to unintended behavior.

Attacker's Prize: The attacker gains the ability to manipulate the smart contract's behavior, potentially leading to unauthorized actions such as transferring funds without permission, altering contract data, or disrupting contract operations.

Real-World Impact

The real-world impact of CVE-2026-114663 can be significant, given the use of Vyper in the Ethereum ecosystem. Successful exploitation could lead to financial losses, disruption of services, or compromise of sensitive data stored or processed by smart contracts. The vulnerability's high CVSS score reflects its potential for severe impact.

Detection & Defense

Immediate Mitigations

To address CVE-2026-114663, users of Vyper should upgrade to a version outside the affected range, specifically to Vyper version 0.5.0b2 or later, once available. Until then, avoid using Vyper versions 0.4.0b1 through 0.5.0b1 for compiling smart contracts.

Detection Strategies

Detection of exploitation attempts can be challenging due to the nature of the vulnerability. However, defenders can monitor for unusual smart contract activity or transactions that deviate from expected behavior. Implementing strict input validation and reviewing smart contract code for potential vulnerabilities can also aid in detection and prevention.

Long-Term Hardening

For long-term hardening, it's essential to keep Vyper and related tools up-to-date. Additionally, code reviews and static analysis of smart contracts can help identify potential issues before deployment. Implementing a defense-in-depth strategy with multiple layers of security can also mitigate the risk of such vulnerabilities.

Key Takeaways

  • CVE-2026-114663 is a high-severity vulnerability in Vyper that can lead to the corruption of validation or accounting logic in smart contracts.
  • The vulnerability is caused by the miscompilation of unfoldable constants and omitted default arguments from imported modules.
  • Immediate mitigation involves upgrading to a non-affected version of Vyper.
  • Detection strategies include monitoring for unusual smart contract activity and implementing strict input validation.
  • Long-term hardening involves keeping software up-to-date, code reviews, and implementing a defense-in-depth strategy.

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