CVE-2026-44490

Axios is a promise based HTTP client for the browser and Node.js. Prior to 0.32.0 and 1.16.0, axios exposes two read-side prototype-pollution gadgets. When Object.prototype is polluted by an upstream dependency in the same process (e.g. lodash _.merge / CVE-2018-16487), axios silently picks up the polluted values. (1) lib/utils.js line 406 builds merge()'s accumulator as result = {}, so result[targetKey] (line 414) walks Object.prototype and the polluted bucket's own keys are copied into the merged headers and ride out on the wire. (2) lib/core/mergeConfig.js line 26 builds the hasOwnProperty descriptor as a plain-object literal. Object.defineProperty reads descriptor.get/descriptor.set via the prototype chain, so a polluted Object.prototype.get or Object.prototype.set makes the call throw TypeError synchronously on every axios request. This vulnerability is fixed in 0.32.0 and 1.16.0.

Axios is a promise based HTTP client for the browser and Node.js. Prior to 0.32.0 and 1.16.0, axios exposes two read-side prototype-pollution gadgets. When Object.prototype is polluted by an upstream dependency in the same process (e.g. lodash _.merge / CVE-2018-16487), axios silently picks up the polluted values. (1) lib/utils.js line 406 builds merge()'s accumulator as result = {}, so result[targetKey] (line 414) walks Object.prototype and the polluted bucket's own keys are copied into the merged headers and ride out on the wire. (2) lib/core/mergeConfig.js line 26 builds the hasOwnProperty descriptor as a plain-object literal. Object.defineProperty reads descriptor.get/descriptor.set via the prototype chain, so a polluted Object.prototype.get or Object.prototype.set makes the call throw TypeError synchronously on every axios request. This vulnerability is fixed in 0.32.0 and 1.16.0.

Summary

axios 1.15.2 exposes two read-side prototype-pollution gadgets. When Object.prototype is polluted by an upstream dependency in the same process (e.g. lodash _.merge / CVE-2018-16487), axios silently picks up the polluted values:

1. Header injection - lib/utils.js line 406 builds merge()'s accumulator as result = {}, so result[targetKey] (line 414) walks Object.prototype and the polluted bucket's own keys are copied into the merged headers and ride out on the wire.
2. Crash DoS - lib/core/mergeConfig.js line 26 builds the hasOwnProperty descriptor as a plain-object literal. Object.defineProperty reads descriptor.get/descriptor.set via the prototype chain, so a polluted Object.prototype.get or Object.prototype.set makes the call throw TypeError synchronously on every axios request.

Affected Properties

| Polluted slot | Effect | |---|---| | Object.prototype.common | injects headers on every method | | Object.prototype.delete / .head / .post / .put / .patch / .query | injects headers on the matching method | | Object.prototype.get | every axios request throws TypeError: Getter must be a function from mergeConfig.js:26 | | Object.prototype.set | every axios request throws TypeError: Setter must be a function from mergeConfig.js:26 |

Per-request headers (axios.request(url, { headers: {...} })) overwrite polluted entries. Polluting Object.prototype.get triggers the crash before any header is built.

Proof of Concept

const axios = require('axios');

// Finding A - header injection
Object.prototype.common = { 'X-Poisoned': 'yes' };
await axios.get('http://api.example.com/users');
// Wire request carries `X-Poisoned: yes`.

// Finding B - crash DoS
Object.prototype.get = { something: 'anything' };
await axios.get('http://api.example.com/users');
// TypeError: Getter must be a function: #<Object>
//     at Function.defineProperty (<anonymous>)
//     at mergeConfig (lib/core/mergeConfig.js:26:10)

Impact

• Server hang (Content-Length: 99999): receiver waits for a body that never arrives. Affects requests with a body.
• CL+TE conflict (Transfer-Encoding: chunked rides alongside axios's auto Content-Length): receiver rejects with 400 Bad Request. Affects requests with a body.
• Response suppression (If-None-Match: *): receiver returns empty 304 Not Modified. Affects GET / HEAD.
• Crash DoS (Object.prototype.get / .set): every axios request fails synchronously with TypeError, not AxiosError, so handlers filtering on error.isAxiosError mishandle the failure.

Attack Flow

flowchart TD
    ROOT["Polluted Object.prototype<br/>via upstream gadget (e.g. lodash &lt;= 4.17.10 _.merge / CVE-2018-16487)<br/>axios &lt;= 1.15.2"]

    ROOT --> CLASS_A["A. Arbitrary HTTP Header Injection<br/>Polluted defaults.headers slot rides along on every outbound axios request"]
    ROOT --> CLASS_B["B. Crash DoS via Object.prototype.get / .set<br/>Polluted descriptor breaks Object.defineProperty in mergeConfig"]

    CLASS_A --> PRE_A["Precondition: header not set per-request by the app<br/>Injected via defaults.headers slot<br/>(common, delete, head, post, put, patch, query)"]

    PRE_A --> PA1["Response Suppression<br/>Trigger: common = {If-None-Match: *}<br/>Affects GET / HEAD"]
    PA1 --> SA1["DoS<br/>304 Not Modified empty"]

    PRE_A --> PA2["Server Hang<br/>Trigger: common = {Content-Length: 99999}<br/>Affects requests with body"]
    PA2 --> SA2["DoS<br/>connection hang"]

    PRE_A --> PA3["CL+TE Conflict<br/>Trigger: common = {Transfer-Encoding: chunked}<br/>Affects requests with body"]
    PA3 --> SA3["DoS<br/>400 Bad Request"]

    CLASS_B --> SB1["DoS<br/>TypeError: Getter / Setter must be a function<br/>Crashes every axios request, not only GET"]

    %% Styles
    style ROOT fill:#f87171,stroke:#991b1b,color:#fff
    style CLASS_A…

Axios is a promise based HTTP client for the browser and Node.js. Prior to 0.32.0 and 1.16.0, axios exposes two read-side prototype-pollution gadgets. When Object.prototype is polluted by an upstream dependency in the same process (e.g. lodash _.merge / CVE-2018-16487), axios silently picks up the polluted values. (1) lib/utils.js line 406 builds merge()'s accumulator as result = {}, so result[targetKey] (line 414) walks Object.prototype and the polluted bucket's own keys are copied into the merged headers and ride out on the wire. (2) lib/core/mergeConfig.js line 26 builds the hasOwnProperty descriptor as a plain-object literal. Object.defineProperty reads descriptor.get/descriptor.set via the prototype chain, so a polluted Object.prototype.get or Object.prototype.set makes the call throw TypeError synchronously on every axios request. This vulnerability is fixed in 0.32.0 and 1.16.0.

Axios is a promise based HTTP client for the browser and Node.js. Prior to 0.32.0 and 1.16.0, axios exposes two read-side prototype-pollution gadgets. When Object.prototype is polluted by an upstream dependency in the same process (e.g. lodash _.merge / CVE-2018-16487), axios silently picks up the polluted values. (1) lib/utils.js line 406 builds merge()'s accumulator as result = {}, so result[targetKey] (line 414) walks Object.prototype and the polluted bucket's own keys are copied into the merged headers and ride out on the wire. (2) lib/core/mergeConfig.js line 26 builds the hasOwnProperty descriptor as a plain-object literal. Object.defineProperty reads descriptor.get/descriptor.set via the prototype chain, so a polluted Object.prototype.get or Object.prototype.set makes the call throw TypeError synchronously on every axios request. This vulnerability is fixed in 0.32.0 and 1.16.0.

Axios is a promise based HTTP client for the browser and Node.js. Prior to 0.32.0 and 1.16.0, axios exposes two read-side prototype-pollution gadgets. When Object.prototype is polluted by an upstream dependency in the same process (e.g. lodash _.merge / CVE-2018-16487), axios silently picks up the polluted values. (1) lib/utils.js line 406 builds merge()'s accumulator as result = {}, so result[targetKey] (line 414) walks Object.prototype and the polluted bucket's own keys are copied into the merged headers and ride out on the wire. (2) lib/core/mergeConfig.js line 26 builds the hasOwnProperty descriptor as a plain-object literal. Object.defineProperty reads descriptor.get/descriptor.set via the prototype chain, so a polluted Object.prototype.get or Object.prototype.set makes the call throw TypeError synchronously on every axios request. This vulnerability is fixed in 0.32.0 and 1.16.0.