CVE-2026-25639: Critical Axios Flaw Triggers Remote Application Crashes, Causing Widespread Service Disruption

Axios – Denial of Service (Application Crash via `proto` Key Injection)

Field	Value
CVE ID	CVE-2026-25639
Affected Product	Axios (Node.js HTTP client library)
Vulnerable Versions	All versions prior to 1.13.5
Fixed Version	1.13.5 and later
CVSS v3.1 Base Score	7.5 (High)
CVSS Vector	AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Severity	High
Exploitability	Low complexity, network-accessible
Exploit Availability	Public technical write-ups and proof-of-concept demonstrations available for educational and defensive validation purposes
Impact	Application crash leading to service disruption or repeated restart loops

Overview

CVE-2026-25639 is a Denial of Service vulnerability in Axios, a widely used HTTP client library for Node.js. The issue occurs due to improper handling of special object keys—specifically __proto__—inside Axios’s internal configuration merging logic.

When an attacker-controlled JSON object containing a __proto__ property is passed into Axios configuration merging functions, the application may throw a TypeError. If that error is not handled properly, the Node.js process may terminate, resulting in a service crash.

This vulnerability does not directly lead to remote code execution or data exposure. However, the availability impact is significant because services relying on Axios for outbound HTTP requests may become unstable or repeatedly crash.

Technical Root Cause

The issue exists in Axios’s internal mergeConfig function.

During configuration merging:

Axios attempts to determine how properties should be merged.
A lookup is performed against an internal merge strategy object.
If the incoming object contains a property named __proto__, JavaScript’s prototype chain behavior is triggered.
The lookup unintentionally resolves to Object.prototype.
The code then attempts to treat that resolved object as a function.
A TypeError is thrown.
If uncaught, the Node.js runtime exits.

This behavior is specific to how JavaScript handles object prototypes and property resolution.

The problem occurs when:

Untrusted JSON input is accepted.
The JSON is parsed into an object.
That object is passed directly into Axios as configuration or merged into an Axios config object.
The application does not sanitize keys before merging.

Attack Scenario

The vulnerability can be exploited remotely when the following conditions are met:

The application exposes an API endpoint accepting JSON input.
User-controlled JSON is parsed using JSON.parse().
The parsed object is directly or indirectly passed into Axios configuration.
The application does not filter special object keys such as __proto__.

An attacker can send a crafted JSON payload containing a __proto__ property.

When the server processes that request and attempts to make an outbound HTTP call using Axios with the attacker-controlled object, the process crashes.

In containerized environments, this may lead to repeated restart loops.
In traditional deployments, it may cause service downtime until manual restart.

Educational Proof-of-Concept

The following payload demonstrates the triggering condition. This should only be tested in controlled lab environments.

Example Payload

{
  "__proto__": {
    "test": "value"
  }
}

If this object is merged directly into Axios configuration on a vulnerable version, the application may throw a TypeError similar to:

TypeError: Object prototype may only be an Object or null

TypeError: mergeMap[configKey] is not a function

Depending on runtime conditions, the process may terminate.

No authentication is required to trigger the issue if the vulnerable endpoint is publicly exposed.

Impact Analysis

Availability

High impact. The service may crash immediately.

Confidentiality

No direct impact.

Integrity

No direct data modification.

Operational Risk

Repeated crash loops
Auto-scaling instability
Health check failures
Increased CPU usage due to restart cycles
Possible cascading failures if the service is upstream of other systems

Exploit Characteristics

Attack Vector: Network
Privileges Required: None
User Interaction: None
Exploitation Complexity: Low
Reliability: High if input is directly merged

The exploit does not require advanced payload crafting. A simple JSON object containing the __proto__ key is sufficient.

Detection Guidance

Detection should focus on two areas:

Suspicious inbound JSON payloads
Application crash indicators

Indicators of Compromise

Application Logs

Stack traces referencing:
- mergeConfig
- Object.prototype
- TypeError
Unexpected Node.js process termination
Repeated restart messages from process managers (PM2, systemd, Docker)

Web Logs

Requests containing "__proto__" in request bodies
Sudden spike in POST requests before crashes

Container Logs

Restart loops
Health check failures

Detection Rules

HTTP Payload Monitoring

index=web sourcetype=access_combined
| search request_body="*__proto__*"
| stats count by clientip, uri, http_method

Application Crash Detection

index=app_logs
| search "TypeError" AND "mergeConfig"
| stats count by host, source

Suspicious JSON Key Detection

http.request.body:*"__proto__"*

Crash Pattern

message:*TypeError* AND message:*mergeConfig*

WAF Detection Logic

Trigger alert if:

Content-Type is application/json
AND request body contains __proto__
AND request method is POST, PUT, or PATCH

Log Sources to Monitor

Web server access logs (Nginx, Apache)
Node.js stdout/stderr logs
Container runtime logs
API gateway logs
WAF logs
Reverse proxy logs
SIEM aggregated application logs

MITRE ATT&CK Mapping

Technique: T1499 – Endpoint Denial of Service
The application process is intentionally forced to terminate.

If used as part of a broader attack campaign:

T1190 – Exploit Public-Facing Application

Remediation

Immediate Action

Upgrade Axios to version 1.13.5 or later.

Official patch link:
https://github.com/axios/axios/releases/tag/v1.13.5

Temporary Mitigation

Reject JSON payloads containing the __proto__ key.
Sanitize parsed objects before merging into configuration.
Implement strict allowlists for configuration properties.
Avoid directly passing user-supplied objects into Axios calls.

Example validation logic:

if (Object.prototype.hasOwnProperty.call(userInput, "__proto__")) {
  throw new Error("Invalid property detected");
}

Secure Coding Recommendations

Use schema validation (Joi, Zod, Ajv) before processing JSON.
Never merge raw user objects into internal configuration structures.
Implement centralized input sanitization middleware.
Enable structured logging for crash visibility.
Configure automatic alerting for repeated process restarts.

Post-Patch Validation

After upgrading:

Confirm installed version: npm list axios
Run regression tests.
Validate that test payload containing __proto__ no longer causes crash.
Monitor logs for 24–48 hours for abnormal restarts.

Risk Assessment Summary

CVE-2026-25639 should be treated as a high-priority availability issue in environments where:

User-controlled JSON is accepted
Axios configuration is dynamically built from request data
Services are public-facing

Although no data theft or remote code execution is involved, repeated crashes can disrupt business operations and impact dependent services.

Final Takeaway

This vulnerability highlights a recurring issue in JavaScript ecosystems involving prototype chain behavior and unsafe object merging. Even though the issue results in a crash rather than code execution, it demonstrates how seemingly small logic flaws can produce significant operational impact.

Immediate patching is strongly recommended. Detection rules should be deployed in parallel to identify attempted exploitation.