fix: mitigate "sequential @import chaining" vulnerability (#5616)

* `test/e2e-cypress/tests/features/xss/` -> `test/e2e-cypress/tests/security`

* add tests

* filter <style> tags out of Markdown fields

* initialize OAuth inputs without applying `value` attribute

Author: shockey

src/core/components/auth/oauth2.jsx

@@ -96,6 +96,7 @@ export default class Oauth2 extends React.Component {
     const AuthError = getComponent("authError")
     const JumpToPath = getComponent("JumpToPath", true)
     const Markdown = getComponent( "Markdown" )
+    const InitializedInput = getComponent("InitializedInput")
 
     const { isOAS3 } = specSelectors
 
@@ -170,10 +171,10 @@ export default class Oauth2 extends React.Component {
             {
               isAuthorized ? <code> ****** </code>
                            : <Col tablet={10} desktop={10}>
-                               <input id="client_id"
+                               <InitializedInput id="client_id"
                                       type="text"
                                       required={ flow === PASSWORD }
-                                      value={ this.state.clientId }
+                                      initialValue={ this.state.clientId }
                                       data-name="clientId"
                                       onChange={ this.onInputChange }/>
                              </Col>
@@ -187,8 +188,8 @@ export default class Oauth2 extends React.Component {
             {
               isAuthorized ? <code> ****** </code>
                            : <Col tablet={10} desktop={10}>
-                               <input id="client_secret"
-                                      value={ this.state.clientSecret }
+                               <InitializedInput id="client_secret"
+                                      initialValue={ this.state.clientSecret }
                                       type="text"
                                       data-name="clientSecret"
                                       onChange={ this.onInputChange }/>

src/core/components/initialized-input.jsx

@@ -0,0 +1,36 @@
+// This component provides an interface that feels like an uncontrolled input
+// to consumers, while providing a `defaultValue` interface that initializes
+// the input's value using JavaScript value property APIs instead of React's 
+// vanilla[0] implementation that uses HTML value attributes.
+//
+// This is useful in situations where we don't want to surface an input's value
+// into the HTML/CSS-exposed side of the DOM, for example to avoid sequential
+// input chaining attacks[1].
+// 
+// [0]: https://github.com/facebook/react/blob/baff5cc2f69d30589a5dc65b089e47765437294b/fixtures/dom/src/components/fixtures/text-inputs/README.md
+// [1]: https://github.com/d0nutptr/sic
+
+import React from "react"
+import PropTypes from "prop-types"
+
+export default class InitializedInput extends React.Component {
+  componentDidMount() {
+    // Set the element's `value` property (*not* the `value` attribute)
+    // once, on mount, if an `initialValue` is provided.
+    if(this.props.initialValue) {
+      this.inputRef.value = this.props.initialValue
+    }
+  }
+
+  render() {
+    // Filter out `value` and `defaultValue`, since we have our own
+    // `initialValue` interface that we provide.
+    // eslint-disable-next-line no-unused-vars, react/prop-types
+    const { value, defaultValue, ...otherProps } = this.props
+    return <input {...otherProps} ref={c => this.inputRef = c} />
+  }
+}
+
+InitializedInput.propTypes = {
+  initialValue: PropTypes.string
+}

src/core/components/providers/markdown.jsx

@@ -51,6 +51,7 @@ export default Markdown
 
 export function sanitizer(str) {
   return DomPurify.sanitize(str, {
-    ADD_ATTR: ["target"]
+    ADD_ATTR: ["target"],
+    FORBID_TAGS: ["style"],
   })
 }

src/core/presets/base.js

@@ -53,6 +53,7 @@ import Headers from "core/components/headers"
 import Errors from "core/components/errors"
 import ContentType from "core/components/content-type"
 import Overview from "core/components/overview"
+import InitializedInput from "core/components/initialized-input"
 import Info, {
   InfoUrl,
   InfoBasePath
@@ -105,6 +106,7 @@ export default function() {
       basicAuth: BasicAuth,
       clear: Clear,
       liveResponse: LiveResponse,
+      InitializedInput,
       info: Info,
       InfoContainer,
       JumpToPath,

test/e2e-cypress/static/documents/petstore-expanded.openapi.yaml

@@ -13,6 +13,8 @@ info:
     url: https://www.apache.org/licenses/LICENSE-2.0.html
 servers:
   - url: http://petstore.swagger.io/api
+security:
+  - Petstore: []
 paths:
   /pets:
     get:
@@ -152,4 +154,13 @@ components:
           type: integer
           format: int32
         message:
-          type: string
+          type: string
+  securitySchemes:
+    Petstore:
+      type: oauth2
+      flows: 
+        implicit:
+          authorizationUrl: https://example.com/api/oauth/dialog
+          scopes:
+            write:pets: modify pets in your account
+            read:pets: read your pets

test/e2e-cypress/static/documents/security/sequential-import-chaining/injection.css

@@ -0,0 +1,7 @@
+* {
+  color: red !important; /* for humans */
+}
+
+h4 {
+  display: none; /* for machines, used to trace whether this sheet is applied */
+}

test/e2e-cypress/static/documents/security/sequential-import-chaining/openapi.yaml

@@ -0,0 +1,10 @@
+openapi: "3.0.0"
+
+info:
+  title: Sequential Import Chaining
+  description: >
+    <h4>This h4 would be hidden by the injected CSS</h4>
+
+    This document tests the ability of a `<style>` tag in a Markdown field to pull in a remote stylesheet using an `@import` directive.
+
+    <style>@import url(/documents/security/sequential-import-chaining/injection.css);</style>

test/e2e-cypress/static/documents/security/sequential-import-chaining/swagger.yaml

@@ -0,0 +1,10 @@
+swagger: "2.0"
+
+info:
+  title: Sequential Import Chaining
+  description: >
+    <h4>This h4 would be hidden by the injected CSS</h4>
+
+    This document tests the ability of a `<style>` tag in a Markdown field to pull in a remote stylesheet using an `@import` directive.
+
+    <style>@import url(/documents/security/sequential-import-chaining/injection.css);</style>

test/e2e-cypress/static/documents/xss/oauth2.yaml renamed to test/e2e-cypress/static/documents/security/xss-oauth2.yaml

@@ -1,6 +1,6 @@
 describe("XSS: OAuth2 authorizationUrl sanitization", () => {
   it("should filter out a javascript URL", () => {
-    cy.visit("/?url=/documents/xss/oauth2.yaml")
+    cy.visit("/?url=/documents/security/xss-oauth2.yaml")
       .window()
       .then(win => {
         let args = null