From fd44e4ba74b7615e196dcafa4f1eddc634c0b44d Mon Sep 17 00:00:00 2001
From: Dan Brown <ssddanbrown@googlemail.com>
Date: Fri, 3 Sep 2021 23:32:42 +0100
Subject: [PATCH] Started application of CSP headers

---
 app/Http/Kernel.php                           |  2 +-
 app/Http/Middleware/ApplyCspRules.php         | 69 +++++++++++++++++++
 app/Http/Middleware/ControlIframeSecurity.php | 37 ----------
 app/Util/HtmlContentFilter.php                |  2 +-
 app/Util/HtmlNonceApplicator.php              | 52 ++++++++++++++
 resources/views/common/custom-head.blade.php  |  2 +-
 6 files changed, 124 insertions(+), 40 deletions(-)
 create mode 100644 app/Http/Middleware/ApplyCspRules.php
 delete mode 100644 app/Http/Middleware/ControlIframeSecurity.php
 create mode 100644 app/Util/HtmlNonceApplicator.php

diff --git a/app/Http/Kernel.php b/app/Http/Kernel.php
index 4b8cdfba4..a98528d0f 100644
--- a/app/Http/Kernel.php
+++ b/app/Http/Kernel.php
@@ -24,7 +24,7 @@ class Kernel extends HttpKernel
      */
     protected $middlewareGroups = [
         'web' => [
-            \BookStack\Http\Middleware\ControlIframeSecurity::class,
+            \BookStack\Http\Middleware\ApplyCspRules::class,
             \BookStack\Http\Middleware\EncryptCookies::class,
             \Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class,
             \Illuminate\Session\Middleware\StartSession::class,
diff --git a/app/Http/Middleware/ApplyCspRules.php b/app/Http/Middleware/ApplyCspRules.php
new file mode 100644
index 000000000..2889d80b0
--- /dev/null
+++ b/app/Http/Middleware/ApplyCspRules.php
@@ -0,0 +1,69 @@
+<?php
+
+namespace BookStack\Http\Middleware;
+
+use Closure;
+use Illuminate\Http\Request;
+use Illuminate\Support\Str;
+use Symfony\Component\HttpFoundation\Response;
+
+
+class ApplyCspRules
+{
+    /**
+     * Handle an incoming request.
+     *
+     * @param Request $request
+     * @param Closure $next
+     *
+     * @return mixed
+     */
+    public function handle($request, Closure $next)
+    {
+        $nonce = Str::random(24);
+        view()->share('cspNonce', $nonce);
+
+        // TODO - Assess whether image/style/iframe CSP rules should be set
+        // TODO - Extract nonce application to custom head content in a way that's cacheable.
+        // TODO - Fix remaining CSP issues and test lots
+
+        $response = $next($request);
+
+        $this->setFrameAncestors($response);
+        $this->setScriptSrc($response, $nonce);
+
+        return $response;
+    }
+
+    /**
+     * Sets CSP 'script-src' headers to restrict the forms of script that can
+     * run on the page.
+     */
+    public function setScriptSrc(Response $response, string $nonce)
+    {
+        $parts = [
+            '\'self\'',
+            '\'nonce-' . $nonce . '\'',
+            '\'strict-dynamic\'',
+        ];
+        $response->headers->set('Content-Security-Policy', 'script-src ' . implode(' ', $parts));
+    }
+
+    /**
+     * Sets CSP "frame-ancestors" headers to restrict the hosts that BookStack can be
+     * iframed within. Also adjusts the cookie samesite options so that cookies will
+     * operate in the third-party context.
+     */
+    protected function setFrameAncestors(Response $response)
+    {
+        $iframeHosts = collect(explode(' ', config('app.iframe_hosts', '')))->filter();
+
+        if ($iframeHosts->count() > 0) {
+            config()->set('session.same_site', 'none');
+        }
+
+        $iframeHosts->prepend("'self'");
+        $cspValue = 'frame-ancestors ' . $iframeHosts->join(' ');
+        $response->headers->set('Content-Security-Policy', $cspValue);
+    }
+}
diff --git a/app/Http/Middleware/ControlIframeSecurity.php b/app/Http/Middleware/ControlIframeSecurity.php
deleted file mode 100644
index 11d9e6d4c..000000000
--- a/app/Http/Middleware/ControlIframeSecurity.php
+++ /dev/null
@@ -1,37 +0,0 @@
-<?php
-
-namespace BookStack\Http\Middleware;
-
-use Closure;
-
-/**
- * Sets CSP headers to restrict the hosts that BookStack can be
- * iframed within. Also adjusts the cookie samesite options
- * so that cookies will operate in the third-party context.
- */
-class ControlIframeSecurity
-{
-    /**
-     * Handle an incoming request.
-     *
-     * @param \Illuminate\Http\Request $request
-     * @param \Closure                 $next
-     *
-     * @return mixed
-     */
-    public function handle($request, Closure $next)
-    {
-        $iframeHosts = collect(explode(' ', config('app.iframe_hosts', '')))->filter();
-        if ($iframeHosts->count() > 0) {
-            config()->set('session.same_site', 'none');
-        }
-
-        $iframeHosts->prepend("'self'");
-
-        $response = $next($request);
-        $cspValue = 'frame-ancestors ' . $iframeHosts->join(' ');
-        $response->headers->set('Content-Security-Policy', $cspValue);
-
-        return $response;
-    }
-}
diff --git a/app/Util/HtmlContentFilter.php b/app/Util/HtmlContentFilter.php
index f3f29ae04..aa395cc45 100644
--- a/app/Util/HtmlContentFilter.php
+++ b/app/Util/HtmlContentFilter.php
@@ -10,7 +10,7 @@ use DOMXPath;
 class HtmlContentFilter
 {
     /**
-     * Remove all of the script elements from the given HTML.
+     * Remove all the script elements from the given HTML.
      */
     public static function removeScripts(string $html): string
     {
diff --git a/app/Util/HtmlNonceApplicator.php b/app/Util/HtmlNonceApplicator.php
new file mode 100644
index 000000000..eb2cf2687
--- /dev/null
+++ b/app/Util/HtmlNonceApplicator.php
@@ -0,0 +1,52 @@
+<?php
+
+namespace BookStack\Util;
+
+use DOMDocument;
+use DOMElement;
+use DOMNodeList;
+use DOMXPath;
+
+class HtmlNonceApplicator
+{
+    /**
+     * Apply the given nonce to all scripts and styles in the given html.
+     */
+    public static function apply(string $html, string $nonce): string
+    {
+        if (empty($html)) {
+            return $html;
+        }
+
+        $html = '<body>' . $html . '</body>';
+        libxml_use_internal_errors(true);
+        $doc = new DOMDocument();
+        $doc->loadHTML(mb_convert_encoding($html, 'HTML-ENTITIES', 'UTF-8'));
+        $xPath = new DOMXPath($doc);
+
+        // Apply to scripts
+        $scriptElems = $xPath->query('//script');
+        static::addNonceAttributes($scriptElems, $nonce);
+
+        // Apply to styles
+        $styleElems = $xPath->query('//style');
+        static::addNonceAttributes($styleElems, $nonce);
+
+        $returnHtml = '';
+        $topElems = $doc->documentElement->childNodes->item(0)->childNodes;
+        foreach ($topElems as $child) {
+            $returnHtml .= $doc->saveHTML($child);
+        }
+
+        return $returnHtml;
+    }
+
+    protected static function addNonceAttributes(DOMNodeList $nodes, string $nonce): void
+    {
+        /** @var DOMElement $node */
+        foreach ($nodes as $node) {
+            $node->setAttribute('nonce', $nonce);
+        }
+    }
+
+}
diff --git a/resources/views/common/custom-head.blade.php b/resources/views/common/custom-head.blade.php
index fa5ba0cc4..3199fc179 100644
--- a/resources/views/common/custom-head.blade.php
+++ b/resources/views/common/custom-head.blade.php
@@ -1,5 +1,5 @@
 @if(setting('app-custom-head') && \Route::currentRouteName() !== 'settings')
 <!-- Custom user content -->
-{!! setting('app-custom-head') !!}
+{!! \BookStack\Util\HtmlNonceApplicator::apply(setting('app-custom-head'), $cspNonce) !!}
 <!-- End custom user content -->
 @endif
\ No newline at end of file