Axios is a promise-based HTTP client for the browser and Node.js. From 1.12.0 until 1.20.0, ResolveConfig reads inherited Symbol.toStringTag, append, and getHeaders properties while resolving FormData headers. A separate same-process prototype-pollution flaw supplies an array or non-plain class instance whose inherited properties make it appear FormData-like; plain objects are blocked. The inherited getHeaders function can return attacker-controlled headers that resolveConfig merges into a fetch adapter request. Attacker-controlled headers can alter authorization, cache, metadata-service, or application-specific request behavior. This issue is fixed in version 1.20.0.

Affected: npm: axios

## Summary

Axios contains a guard in the Node HTTP adapter to avoid using an inherited `Object.prototype.getHeaders` as a FormData header source. The fetch adapter calls the shared `resolveConfig()` helper before dispatch, and that helper lacks the same guard. If another vulnerability pollutes `Object.prototype` with FormData-like properties and `getHeaders()`, the fetch adapter can merge attacker-controlled headers into the outbound request.

Axios does not create the prototype pollution source. This is a read-side gadget in the fetch adapter configuration path.

## Impact

An attacker with a prior same-process prototype-pollution primitive can inject headers into fetch-adapter requests. Depending on the target service, this may affect authorization, metadata-service access, cache behavior, conditional request handling, or other application-specific header logic.

Plain objects are blocked by current FormData detection. The confirmed path uses arrays or non-plain class instances whose prototype chain can resolve polluted FormData-like properties.

## Affected Functionality

Affected:

- Fetch adapter requests. - `resolveConfig()` handling of `utils.isFormData(data)`. - Request bodies that can be spoofed as FormData through inherited `Symbol.toStringTag`, `append`, and `getHeaders`.

Not affected:

- Node HTTP adapter's later FormData header path, which checks `data.getHeaders !== Object.prototype.getHeaders`. - Plain object request bodies rejected by current `isFormData()`…

hono: hono/jsx: Cross-Site Scripting via Unescaped Strings axios: axios: Security control bypass via unapplied HTTP/2 proxy and DNS settings axios: Axios: Outbound HTTP header injection via prototype pollution in fetch adapter axios: Axios: Denial of Service via unhandled error in HTTP/2 session initialization axios: axios: Unintended HTTP method override via prototype pollution gadget axios: Axios: Denial of Service via malformed data URLs axios: Axios: HTTP header injection via inherited prototype properties axios: axios: Request socket hijacking via inherited createConnection property axios: axios: Denial of Service via crafted redirect hostname axios: Axios: Server-Side Request Forgery via bypassed redirect restrictions in fetch adapter axios: Axios: Outbound HTTP request manipulation via fetch adapter prototype pollution axios: axios: Denial of Service via prototype pollution gadget in form serialization

Affected: Ubuntu:Pro:20.04:LTS: node-axios, Ubuntu:Pro:22.04:LTS: node-axios, Ubuntu:Pro:24.04:LTS: node-axios, Ubuntu:Pro:26.04:LTS: node-axios

Axios is a promise-based HTTP client for the browser and Node.js. From 1.12.0 until 1.20.0, ResolveConfig reads inherited Symbol.toStringTag, append, and getHeaders properties while resolving FormData headers. A separate same-process prototype-pollution flaw supplies an array or non-plain class instance whose inherited properties make it appear FormData-like; plain objects are blocked. The inherited getHeaders function can return attacker-controlled headers that resolveConfig merges into a fetch adapter request. Attacker-controlled headers can alter authorization, cache, metadata-service, or application-specific request behavior. This issue is fixed in version 1.20.0.