{"id":"GHSA-898c-q2cr-xwhg","summary":"axios has DoS & Header Injection via Prototype Pollution Read-Side Gadgets in axios merge functions","details":"## Summary\n\naxios `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](https://nvd.nist.gov/vuln/detail/CVE-2018-16487)), axios silently picks up the polluted values:\n\n1. **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.\n2. **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.\n\n## Affected Properties\n\n| Polluted slot | Effect |\n|---|---|\n| `Object.prototype.common` | injects headers on every method |\n| `Object.prototype.delete` / `.head` / `.post` / `.put` / `.patch` / `.query` | injects headers on the matching method |\n| `Object.prototype.get` | every axios request throws `TypeError: Getter must be a function` from `mergeConfig.js:26` |\n| `Object.prototype.set` | every axios request throws `TypeError: Setter must be a function` from `mergeConfig.js:26` |\n\nPer-request headers (`axios.request(url, { headers: {...} })`) overwrite polluted entries. Polluting `Object.prototype.get` triggers the crash before any header is built.\n\n## Proof of Concept\n\n```javascript\nconst axios = require('axios');\n\n// Finding A - header injection\nObject.prototype.common = { 'X-Poisoned': 'yes' };\nawait axios.get('http://api.example.com/users');\n// Wire request carries `X-Poisoned: yes`.\n\n// Finding B - crash DoS\nObject.prototype.get = { something: 'anything' };\nawait axios.get('http://api.example.com/users');\n// TypeError: Getter must be a function: #\u003cObject\u003e\n//     at Function.defineProperty (\u003canonymous\u003e)\n//     at mergeConfig (lib/core/mergeConfig.js:26:10)\n```\n\n## Impact\n\n- **Server hang** (`Content-Length: 99999`): receiver waits for a body that never arrives. Affects requests with a body.\n- **CL+TE conflict** (`Transfer-Encoding: chunked` rides alongside axios's auto `Content-Length`): receiver rejects with `400 Bad Request`. Affects requests with a body.\n- **Response suppression** (`If-None-Match: *`): receiver returns empty `304 Not Modified`. Affects GET / HEAD.\n- **Crash DoS** (`Object.prototype.get` / `.set`): every axios request fails synchronously with `TypeError`, not `AxiosError`, so handlers filtering on `error.isAxiosError` mishandle the failure.\n\n## Attack Flow\n\n```mermaid\nflowchart TD\n    ROOT[\"Polluted Object.prototype\u003cbr/\u003evia upstream gadget (e.g. lodash <= 4.17.10 _.merge / CVE-2018-16487)\u003cbr/\u003eaxios <= 1.15.2\"]\n\n    ROOT --\u003e CLASS_A[\"A. Arbitrary HTTP Header Injection\u003cbr/\u003ePolluted defaults.headers slot rides along on every outbound axios request\"]\n    ROOT --\u003e CLASS_B[\"B. Crash DoS via Object.prototype.get / .set\u003cbr/\u003ePolluted descriptor breaks Object.defineProperty in mergeConfig\"]\n\n    CLASS_A --\u003e PRE_A[\"Precondition: header not set per-request by the app\u003cbr/\u003eInjected via defaults.headers slot\u003cbr/\u003e(common, delete, head, post, put, patch, query)\"]\n\n    PRE_A --\u003e PA1[\"Response Suppression\u003cbr/\u003eTrigger: common = {If-None-Match: *}\u003cbr/\u003eAffects GET / HEAD\"]\n    PA1 --\u003e SA1[\"DoS\u003cbr/\u003e304 Not Modified empty\"]\n\n    PRE_A --\u003e PA2[\"Server Hang\u003cbr/\u003eTrigger: common = {Content-Length: 99999}\u003cbr/\u003eAffects requests with body\"]\n    PA2 --\u003e SA2[\"DoS\u003cbr/\u003econnection hang\"]\n\n    PRE_A --\u003e PA3[\"CL+TE Conflict\u003cbr/\u003eTrigger: common = {Transfer-Encoding: chunked}\u003cbr/\u003eAffects requests with body\"]\n    PA3 --\u003e SA3[\"DoS\u003cbr/\u003e400 Bad Request\"]\n\n    CLASS_B --\u003e SB1[\"DoS\u003cbr/\u003eTypeError: Getter / Setter must be a function\u003cbr/\u003eCrashes every axios request, not only GET\"]\n\n    %% Styles\n    style ROOT fill:#f87171,stroke:#991b1b,color:#fff\n    style CLASS_A fill:#fb923c,stroke:#9a3412,color:#fff\n    style CLASS_B fill:#fb923c,stroke:#9a3412,color:#fff\n    style PRE_A fill:#e2e8f0,stroke:#64748b,color:#1e293b\n    style PA1 fill:#fbbf24,stroke:#92400e,color:#000\n    style PA2 fill:#fbbf24,stroke:#92400e,color:#000\n    style PA3 fill:#fbbf24,stroke:#92400e,color:#000\n    style SA1 fill:#ef4444,stroke:#991b1b,color:#fff\n    style SA2 fill:#ef4444,stroke:#991b1b,color:#fff\n    style SA3 fill:#ef4444,stroke:#991b1b,color:#fff\n    style SB1 fill:#ef4444,stroke:#991b1b,color:#fff\n```\n\n## Root Cause\n\n**Finding A.** `lib/utils.js:404-429`'s `merge()` creates `result = {}` at line 406. The dangerous-keys filter on lines 408-411 blocks the write side, but the read at line 414 (`isPlainObject(result[targetKey])`) still walks the prototype chain. When `targetKey` matches a polluted slot, `result[targetKey]` returns the polluted nested object, and the recursive `merge(result[targetKey], val)` on line 415 iterates that object's own keys via `forEach` and copies them as own properties into the new accumulator. Those keys flow through `mergeConfig.js:35` → `Axios.js:148` (`utils.merge(headers.common, headers[config.method])`) → `Axios.js:155` (`AxiosHeaders.concat(...)`) → onto the wire via `http.js:677` (`headers: headers.toJSON()`) → `http.js:767` (`transport.request(options, ...)`).\n\n**Finding B.** `lib/core/mergeConfig.js:25` correctly makes `config = Object.create(null)`, but the descriptor passed on line 26 is a plain-object literal - its `get`/`set` lookups walk `Object.prototype`. A polluted non-function `Object.prototype.get` or `.set` makes `Object.defineProperty` throw `TypeError: Getter must be a function` (or `Setter must be a function`) before the call returns. The descriptor is built unconditionally on every `mergeConfig` invocation, so every axios request throws - POST, PUT, DELETE, PATCH, HEAD, QUERY, not only GET.\n\n## Suggested Fix\n\nUse null-prototype objects in place of the plain-object literals at `lib/utils.js:406` and `lib/core/mergeConfig.js:26-31`. The same descriptor pattern recurs at `lib/core/AxiosError.js:37`, `lib/core/AxiosHeaders.js:100`, `lib/utils.js:447/454/492/498`, and `lib/adapters/adapters.js:28/32`.\n\n## Resources\n\n- [CVE-2018-16487](https://nvd.nist.gov/vuln/detail/CVE-2018-16487) - `lodash.merge` prototype pollution in `lodash \u003c= 4.17.10`\n- [CWE-1321](https://cwe.mitre.org/data/definitions/1321.html) - Improperly Controlled Modification of Object Prototype Attributes","aliases":["CVE-2026-44490"],"modified":"2026-07-17T21:06:47.520497328Z","published":"2026-05-29T15:54:57Z","database_specific":{"nvd_published_at":"2026-06-11T17:16:33Z","cwe_ids":["CWE-1321"],"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2026-05-29T15:54:57Z"},"references":[{"type":"WEB","url":"https://github.com/axios/axios/security/advisories/GHSA-898c-q2cr-xwhg"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2018-16487"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-44490"},{"type":"PACKAGE","url":"https://github.com/axios/axios"}],"affected":[{"package":{"name":"axios","ecosystem":"npm","purl":"pkg:npm/axios"},"ranges":[{"type":"SEMVER","events":[{"introduced":"1.0.0"},{"fixed":"1.16.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-898c-q2cr-xwhg/GHSA-898c-q2cr-xwhg.json"}},{"package":{"name":"axios","ecosystem":"npm","purl":"pkg:npm/axios"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.32.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-898c-q2cr-xwhg/GHSA-898c-q2cr-xwhg.json","last_known_affected_version_range":"\u003c= 0.31.1"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L"}]}