CVE-2026-101902

Axios is a promise-based HTTP client for the browser and Node.js. From 0.27.2 until 0.34.0 and 1.20.0, Axios default-instance requests that omit an explicit method can read an inherited method value from Object.prototype. If another vulnerability in the same process pollutes Object.prototype.method, calls such as axios.request({ url }) and axios({ url }) can send a state-changing HTTP method instead of the expected default GET. Axios does not create the prototype pollution source. This is a read-side gadget in axios request dispatch. This issue is fixed in version 0.34.0 and 1.20.0.

Axios is a promise-based HTTP client for the browser and Node.js. From 0.27.2 until 0.34.0 and 1.20.0, Axios default-instance requests that omit an explicit method can read an inherited method value from Object.prototype. If another vulnerability in the same process pollutes Object.prototype.method, calls such as axios.request({ url }) and axios({ url }) can send a state-changing HTTP method instead of the expected default GET. Axios does not create the prototype pollution source. This is a read-side gadget in axios request dispatch. This issue is fixed in version 0.34.0 and 1.20.0.

Summary

Axios default-instance requests that omit an explicit method can read an inherited method value from Object.prototype. If another vulnerability in the same process pollutes Object.prototype.method, calls such as axios.request({ url }) and axios({ url }) can send a state-changing HTTP method instead of the expected default GET.

Axios does not create the prototype pollution source. This is a read-side gadget in axios request dispatch.

Impact

In an affected application with a separate prototype-pollution primitive, an attacker can change axios default-instance requests that omit method from GET to methods such as DELETE, POST, PUT, or PATCH. The practical impact depends on the target endpoint and can include unintended writes, deletion, or other state changes.

Method aliases such as axios.get(url) and requests with an explicit own method are not affected by the confirmed method path.

Affected Functionality

Affected:

• Default axios instance calls: axios.request({ url }).
• Callable shorthand: axios({ url }).
• Requests where no own config.method is provided.

Not affected in the confirmed method PoC:

• axios.get(url) and other method aliases.
• axios.request({ url, method: 'GET' }).
• axios.create().request({ url }) when the created instance defaults are produced by current mergeConfig() and do not inherit from Object.prototype.

Technical Details

lib/core/Axios.js sets the request method with:

config.method = (config.method || this.defaults.method || 'get').toLowerCase();

mergeConfig() now returns a null-prototype request config, so config.method is safe from Object.prototype. However, the default axios instance stores the module defaults object as this.defaults, and that defaults object is a normal object. If Object.prototype.method exists, this.defaults.method resolves to the polluted inherited value.

Local verification on axios 1.18.1 showed a default-instance axios.request({ url }) request reaching a loopback server as DELETE after Object.prototype.method = 'DELETE'.

Proof of Concept of Attack

Constrained local demonstration:

Object.prototype.method = 'DELETE';
try {
  await axios.request({ url: 'http://127.0.0.1:<port>/resource' });
} finally {
  delete Object.prototype.method;
}

Expected safe behavior is a GET request. Current affected behavior sends DELETE on the default instance when no method is provided.

Workarounds

Use explicit method aliases such as axios.get() or set an own method on request configs. Avoid default-instance shorthand for requests in processes where prototype pollution is suspected or possible.

<details> <summary><h3>Original report</h3></summary>

Summary

Axios 1.17.0 contains a read-side prototype-pollution gadget in the default Axios instance. If another vulnerability in the same Node.js process pollutes Object.prototype.method, default-instance calls such as axios.request({ url }) and axios({ url }) can be forced to use an attacker-controlled HTTP method, such as DELETE, instead of the expected default GET.

Axios does not create the prototype pollution by itself. The issue is that Axios reads fallback values from this.defaults without an own-property guard, allowing inherited values from Object.prototype to influence request behavior.

This should be treated as a prototype-pollution gadget, not as a standalone prototype-pollution source. In other words, Axios is not the component that lets the attacker write to Object.prototype; Axios is the component that becomes dangerous after Object.prototype has already been polluted by another bug in the same process.

Details

The vulnerable fallback read is in lib/core/Axios.js:

// Set config.allowAbsoluteUrls
if (config.allowAbsoluteUrls !== undefined) {
  // do nothing
} else if (this.defaults.allowAbsoluteUrls !== undefined) {
  config.allowAbsoluteUrls =…

Axios is a promise-based HTTP client for the browser and Node.js. From 0.27.2 until 0.34.0 and 1.20.0, Axios default-instance requests that omit an explicit method can read an inherited method value from Object.prototype. If another vulnerability in the same process pollutes Object.prototype.method, calls such as axios.request({ url }) and axios({ url }) can send a state-changing HTTP method instead of the expected default GET. Axios does not create the prototype pollution source. This is a read-side gadget in axios request dispatch. This issue is fixed in version 0.34.0 and 1.20.0.

Axios is a promise-based HTTP client for the browser and Node.js. From 0.27.2 until 0.34.0 and 1.20.0, Axios default-instance requests that omit an explicit method can read an inherited method value from Object.prototype. If another vulnerability in the same process pollutes Object.prototype.method, calls such as axios.request({ url }) and axios({ url }) can send a state-changing HTTP method instead of the expected default GET. Axios does not create the prototype pollution source. This is a read-side gadget in axios request dispatch. This issue is fixed in version 0.34.0 and 1.20.0.

Axios is a promise-based HTTP client for the browser and Node.js. From 0.27.2 until 0.34.0 and 1.20.0, Axios default-instance requests that omit an explicit method can read an inherited method value from Object.prototype. If another vulnerability in the same process pollutes Object.prototype.method, calls such as axios.request({ url }) and axios({ url }) can send a state-changing HTTP method instead of the expected default GET. Axios does not create the prototype pollution source. This is a read-side gadget in axios request dispatch. This issue is fixed in version 0.34.0 and 1.20.0.