CVE-2018-10895: Fix CSRF issues with qute://settings/set URLv1.3.x

In ffc29ee043ae7336d9b9dcc029a05bf7a3f994e8 (part of v1.0.0), a
qute://settings/set URL was added to change settings.

Contrary to what I apparently believed at the time, it *is* possible for
websites to access `qute://*` URLs (i.e., neither QtWebKit nor QtWebEngine
prohibit such requests, other than the usual cross-origin rules).

In other words, this means a website can e.g. have an `<img>` tag which loads a
`qute://settings/set` URL, which then sets `editor.command` to a bash script.
The result of that is arbitrary code execution.

Fixes #4060
See #2332

(cherry picked from commit 43e58ac865ff862c2008c510fc5f7627e10b4660)

1 files changed, 24 insertions, 5 deletions

diff --git a/qutebrowser/browser/webkit/network/webkitqutescheme.py b/qutebrowser/browser/webkit/network/webkitqutescheme.py
index d732b6ab0..b6f99437a 100644
--- a/qutebrowser/browser/webkit/network/webkitqutescheme.py
+++ b/qutebrowser/browser/webkit/network/webkitqutescheme.py
@@ -21,27 +21,46 @@
 
 import mimetypes
 
-from PyQt5.QtNetwork import QNetworkReply
+from PyQt5.QtCore import QUrl
+from PyQt5.QtNetwork import QNetworkReply, QNetworkAccessManager
 
 from qutebrowser.browser import pdfjs, qutescheme
 from qutebrowser.browser.webkit.network import networkreply
 from qutebrowser.utils import log, usertypes, qtutils
 
 
-def handler(request):
+def handler(request, operation, current_url):
     """Scheme handler for qute:// URLs.
 
     Args:
         request: QNetworkRequest to answer to.
+        operation: The HTTP operation being done.
+        current_url: The page we're on currently.
 
     Return:
         A QNetworkReply.
     """
+    if operation != QNetworkAccessManager.GetOperation:
+        return networkreply.ErrorNetworkReply(
+            request, "Unsupported request type",
+            QNetworkReply.ContentOperationNotPermittedError)
+
+    url = request.url()
+
+    if ((url.scheme(), url.host(), url.path()) ==
+            ('qute', 'settings', '/set')):
+        if current_url != QUrl('qute://settings/'):
+            log.webview.warning("Blocking malicious request from {} to {}"
+                                .format(current_url.toDisplayString(),
+                                        url.toDisplayString()))
+            return networkreply.ErrorNetworkReply(
+                request, "Invalid qute://settings request",
+                QNetworkReply.ContentAccessDenied)
+
     try:
-        mimetype, data = qutescheme.data_for_url(request.url())
+        mimetype, data = qutescheme.data_for_url(url)
     except qutescheme.NoHandlerFound:
-        errorstr = "No handler found for {}!".format(
-            request.url().toDisplayString())
+        errorstr = "No handler found for {}!".format(url.toDisplayString())
         return networkreply.ErrorNetworkReply(
             request, errorstr, QNetworkReply.ContentNotFoundError)
     except qutescheme.QuteSchemeOSError as e: