CVE-2026-101904: Axios: Header Injection via Inherited headers After Minimal Interceptor

Axios request interceptors may return a replacement config object. If an interceptor returns a plain object without an own headers property, dispatchRequest() later evaluates config.headers and can resolve an inherited Object.prototype.headers value. In a process where another vulnerability has polluted Object.prototype.headers, axios can send attacker-controlled headers.

Axios does not create the prototype pollution source, and the interceptor itself is trusted caller code. The vulnerable behavior is the post-interceptor axios config read that reopens a prototype-pollution gadget after earlier null-prototype config hardening.

Axios 1.17.0 blocks the old Object.prototype.common header bucket gadget. However, if a request interceptor rebuilds a minimal config object and omits headers, dispatchRequest() reads inherited Object.prototype.headers.

This allows attacker-controlled headers to be placed on the wire.