GHSA-pf86-5x62-jrwf

Summary

When Object.prototype has been polluted by any co-dependency with keys that axios reads without a hasOwnProperty guard, an attacker can (a) silently intercept and modify every JSON response before the application sees it, or (b) fully hijack the underlying HTTP transport, gaining access to request credentials, headers, and body. The precondition is prototype pollution from a separate source in the same process -- lodash < 4.17.21, or any of several other common npm packages with known PP vectors. The two gadgets confirmed here work independently.

Background: how mergeConfig builds the config object

Every axios request goes through Axios._request in lib/core/Axios.js#L76:

config = mergeConfig(this.defaults, config);

Inside mergeConfig, the merged config is built as a plain {} object (lib/core/mergeConfig.js#L20):

const config = {};

A plain {} inherits from Object.prototype. mergeConfig only iterates Object.keys({ ...config1, ...config2 }) (line 99), which is a spread of own properties. Any key that is absent from both this.defaults and the per-request config will never be set as an own property on the merged config. Reading that key later on the merged config falls through to Object.prototype. That is the root mechanism behind all gadgets below.

Gadget 1: parseReviver -- response tampering and exfiltration

Introduced in: v1.12.0 (commit 2a97634, PR #5926) Affected range: >= 1.12.0, <= 1.13.6

Root cause

The default transformResponse function calls JSON.parse(data, this.parseReviver):

return JSON.parse(data, this.parseReviver);

this is the merged config. parseReviver...