Major Security Flaw in Axios
A significant security vulnerability has been identified in Axios, a widely-used HTTP client library within the JavaScript ecosystem. This vulnerability, known as CVE-2026-25639, poses a severe threat by enabling remote attackers to induce a Denial-of-Service (DoS) condition, leading to the crashing of Node.js servers with just a single malicious request.
Understanding the Axios Vulnerability
The root of the issue lies in the mergeConfig function in Axios, which is responsible for combining multiple configuration objects. The flaw manifests when this function encounters a configuration object with __proto__ as a key, causing the application to crash.
Typically, Axios merges configuration properties by iterating over them. However, a malicious JSON object containing __proto__ disrupts the internal logic. When Axios attempts to execute a merge strategy, it mistakenly accesses Object.prototype, which is an object rather than a function, resulting in a TypeError and an immediate crash.
Impact and Affected Versions
This security flaw is distinct from Prototype Pollution vulnerabilities, as the application crashes before any property pollution occurs. With a high severity rating (CVSS 7.5), this vulnerability affects Axios versions up to 1.13.4 available on npm. The attack complexity is low, making it easier for attackers to exploit.
The vulnerability particularly threatens applications that accept user-controlled inputs, such as JSON bodies, parse these inputs using JSON.parse(), and incorporate the resulting objects into Axios configurations. An attacker can trigger a server crash by sending a payload like {“__proto__”: {“x”: 1}}, effectively taking the service offline.
Mitigation and Recommendations
The Axios development team has addressed this issue by releasing a patch in version 1.13.5, which correctly handles the __proto__ key to prevent TypeErrors. Developers using affected versions are strongly advised to update their dependencies to the latest version using npm or yarn to mitigate this risk.
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