GHSA-3g43-6gmg-66jw axios Vulnerable to Credential Theft and Response Hijacking via Prototype Pollution Gadget in Config Merge

• npm axios: >= 1.0.0, < 1.15.2 → fixed in 1.15.2 • npm axios: >= 0.19.0, < 0.31.1 → fixed in 0.31.1

Summary Axios versions before the fixed releases contain prototype-pollution gadgets in request config processing. If another vulnerability in the same JavaScript process has already polluted `Object.prototype.transformResponse`, affected Axios versions may treat that inherited value as request configuration or as an option validator. Axios does not itself create the prototype pollution. Exploitability requires a separate prototype-pollution vulnerability or equivalent attacker control over `Object.prototype` before Axios creates a request. Impact For ordinary prototype-pollution primitives that can only assign JSON-like values, this issue primarily results in request failures or denial-of-service attacks. If the attacker can pollute `Object.prototype.transformResponse` with a function, affected versions of Axios may execute it. In fully affected versions, the function can observe response data and request config, including URL, headers, and `auth`, and can change the response data returned to application code. This function-valued condition is important. Most query-string or JSON parser prototype-pollution bugs cannot create JavaScript functions on their own, so credential exposure and response tampering are conditional rather than automatic consequences of such bugs. Affected Functionality The affected functionality is Axios request config processing and response transformation. Affected use requires all of the following: • An affected Axios version. • A polluted `Object.prototype` in the same process or browser context. • Pollution before Axios merges or validates the request config. • A polluted key relevant to Axios config, especially `transformResponse`. This is not specific to the Node HTTP adapter. Browser and Node usage can both pass through the shared config/transform pipeline, though real-world exploitability depends on the surrounding application and any helper vulnerabilities. Technical Details In affected versions, `mergeConfig()` reads config values through normal property access. For config keys present in Axios defaults, including `transformResponse`, a missing own property on the request config can fall through to `Object.prototype`. In the fully affected path, this means `Object.prototype.transformResponse` can replace Axios's default response transform. The selected transform is later executed by `transformData()` with the request config as `this`. Some later affected v1 releases guarded the merge path but still used inherited properties while looking up validators in `validator.assertOptions()`. In that narrower case, a polluted function can still run during config validation and inspect the config argument, but it does not replace the response transform. Fixed versions use own-property checks and null-prototype config objects, so inherited `Object.prototype` values are not treated as Axios config or validator schema entries. Proof of Concept of Attack ```js import http from 'http'; import axios from 'axios'; const seen = []; const server = http.createServer((req, res) => { res.setHeader('Content-Type', 'application/json'); res.end(JSON.stringify({ secret: 'response-secret' })); }); await new Promise(resolve => server.listen(0, '127.0.0.1', resolve)); Object.prototype.transformResponse = function pollutedTransform(data, headers, status) { if (headers && typeof status === 'number') { seen.push({ url: this.url, username: this.auth && this.auth.username, password: this.auth && this.auth.password, responseData: data }); return { hijacked: true }; } return true; }; try { const { port } = server.address(); const response = await axios.get(`http://127.0.0.1:${port}/users`, { auth: { username: 'svc-account', password: 'prod-secret-key-123' } }); console.log(response.data); // { hijacked: true } console.log(seen[0]); // request config plus original response body } finally { delete Object.prototype.transformResponse; server.close(); } ``` Expected result on fully affected versions: the polluted transform runs, captures request config and response data, and replaces the response returned to the caller. Expected result on fixed versions: the polluted transform is ignored, and the original response is returned. Original source report Summary The Axios library is vulnerable to a Prototype Pollution "Gadget" attack that allows any `Object.prototype` pollution in the application's dependency tree to be escalated into credential theft and response hijacking across all Axios requests. The `mergeConfig()` function reads config properties via standard property access (`config2[prop]`), which traverses the JavaScript prototype chain. When `Object.prototype.transformResponse` is polluted with a function, it overrides the default JSON response parser for every request. The injected function executes with `this = config`, exposing `auth.username`, `auth.password`, request URL, and all headers. Severity: High (CVSS 8.2) Affected Versions: All versions (v0.x - v1.x including v1.15.0) Vulnerable Component: `lib/core/mergeConfig.js` (Config Merge) + `lib/core/transformData.js` (Transform Execution) CWE • CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') CVSS 3.1 Score: 9.4 (High) Vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:H` | Metric | Value | Justification | |---|---|---| | Attack Vector | Network | PP is triggered remotely via any vulnerable dependency | | Attack Complexity | Low | Once PP exists, a single property assignment exploits axios. Consistent with GHSA-fvcv-3m26-pcqx scoring | | Privileges Required | None | No authentication needed | | User Interaction | None | No user interaction required | | Scope | Unchanged | Credential theft occurs within the same application process | | Confidentiality | High | `this.auth.password`, `this.url`, original response data all exfiltrated | | Integrity | Low | Response data is replaced with `true` — attacker cannot return arbitrary data due to `assertOptions` constraint (see below) | | Availability | High | Polluting with an array value causes `TypeError: validator is not a function` crash (DoS) on every request | Relationship to GHSA-fvcv-3m26-pcqx This vulnerability is in the same class as GHSA-fvcv-3m26-pcqx ("Unrestricted Cloud Metadata Exfiltration via Header Injection Chain"), which was also a PP gadget in axios rated Critical. Both require zero direct user input and exploit `mergeConfig`'s prototype chain traversal. | Factor | GHSA-fvcv-3m26-pcqx | This Vulnerability | |---|---|---| | Attack vector | PP → Header injection → Request smuggling | PP → Transform function override → Credential theft | | Fixed by 1.15.0 header sanitization? | Yes | No — different code path | | Affects | Requests using form-data package | All requests (transformResponse is in defaults) | | Impact | AWS IMDSv2 bypass, cloud compromise | Credential theft (auth, API keys), response hijacking, DoS | Usage of "Helper" Vulnerabilities This vulnerability requires Zero Direct User Input. If an attacker can pollute `Object.prototype` via any other library in the stack (e.g., `qs`, `minimist`, `lodash`, `body-parser`), Axios will automatically pick up the polluted `transformResponse` property during its config merge. The critical difference from GHSA-fvcv-3m26-pcqx: this vector was NOT fixed by the header sanitization patch in v1.15.0, because it does not use headers at all — it injects a function into the response processing pipeline. Proof of Concept 1. The Setup (Simulated Pollution) Imagine a scenario where a known vulnerability exists in a query parser. The attacker sends a payload that sets: ```javascript Object.prototype.transformResponse = function(data, headers, status) { // Steal credentials via this context (this = full request config) if (this && this.url && typeof dat…