CVE-2026-101900: Axios: Fetch Adapter Header Injection via Inherited FormData getHeaders

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.

The Node HTTP adapter contains a guard that prevents Object.prototype.getHeaders from being used as a FormData header source. The shared resolveConfig() helper does not have the same guard. The fetch adapter calls resolveConfig(), so it can still merge headers returned by inherited data.getHeaders().

This is a patch mismatch for the FormData prototype-pollution header-injection class.