epiphany: fix CVEs

Backport patch [1] to fix below CVEs:
 - CVE-2021-45085
 - CVE-2021-45086
 - CVE-2021-45087
 - CVE-2021-45088

[1] https://sources.debian.org/data/main/e/epiphany-browser/3.38.2-1+deb11u2/debian/patches/encode-untrusted-data.patch

(From OE-Core rev: 125c6f5770542c3b509336b92d6c45c0c955027e)

Signed-off-by: Mingli Yu <mingli.yu@windriver.com>
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-gnome/epiphany/epiphany_3.38.2.bb

@@ -18,6 +18,7 @@ SRC_URI = "${GNOME_MIRROR}/${GNOMEBN}/${@gnome_verdir("${PV}")}/${GNOMEBN}-${PV}
            file://0002-help-meson.build-disable-the-use-of-yelp.patch \
            file://migrator.patch \
            file://distributor.patch \
+           file://encode-untrusted-data.patch \
            "
 SRC_URI[archive.sha256sum] = "8b05f2bcc1e80ecf4a10f6f01b3285087eb4cbdf5741dffb8c0355715ef5116d"
 

meta/recipes-gnome/epiphany/files/encode-untrusted-data.patch

@@ -0,0 +1,707 @@
+From: Michael Catanzaro <mcatanzaro@redhat.com>
+Subject: Properly encode untrusted data when injecting into trusted pages
+
+CVE: CVE-2021-45085 CVE-2021-45086 CVE-2021-45087 CVE-2021-45088
+
+Upstream-Status: Backport [https://gitlab.gnome.org/GNOME/epiphany/-/compare/c27a8180e12e6ec92292dcf53b9243815ad9aa2e...abac58c5191b7d653fbefa8d44e5c2bd4d002825?from_project_id=1906]
+
+Signed-off-by: Mingli Yu <mingli.yu@windriver.com>
+Index: epiphany-browser/embed/ephy-about-handler.c
+===================================================================
+--- epiphany-browser.orig/embed/ephy-about-handler.c
++++ epiphany-browser/embed/ephy-about-handler.c
+@@ -27,6 +27,7 @@
+ #include "ephy-file-helpers.h"
+ #include "ephy-flatpak-utils.h"
+ #include "ephy-history-service.h"
++#include "ephy-output-encoding.h"
+ #include "ephy-prefs.h"
+ #include "ephy-settings.h"
+ #include "ephy-smaps.h"
+@@ -263,16 +264,34 @@ handle_applications_finished_cb (EphyAbo
+ 
+     for (p = applications; p; p = p->next) {
+       EphyWebApplication *app = (EphyWebApplication *)p->data;
+-
++      g_autofree char *html_encoded_id = NULL;
++      g_autofree char *encoded_icon_url = NULL;
++      g_autofree char *encoded_name = NULL;
++      g_autofree char *encoded_url = NULL;
++      g_autofree char *js_encoded_id = NULL;
++      g_autofree char *encoded_install_date = NULL;
++
++      /* Most of these fields are untrusted. The web app suggests its own title,
++       * which gets used in the app ID and icon URL. The main URL could contain
++       * anything. Install date is the only trusted field here in that it's
++       * constructed by Epiphany, but it's a freeform string and we're encoding
++       * everything else here anyway, so might as well encode this too.
++       */
++      html_encoded_id = ephy_encode_for_html_attribute (app->id);
++      encoded_icon_url = ephy_encode_for_html_attribute (app->icon_url);
++      encoded_name = ephy_encode_for_html_entity (app->name);
++      encoded_url = ephy_encode_for_html_entity (app->url);
++      js_encoded_id = ephy_encode_for_javascript (app->id);
++      encoded_install_date = ephy_encode_for_html_entity (app->install_date);
+       g_string_append_printf (data_str,
+                               "<tbody><tr id =\"%s\">"
+                               "<td class=\"icon\"><img width=64 height=64 src=\"file://%s\"></img></td>"
+                               "<td class=\"data\"><div class=\"appname\">%s</div><div class=\"appurl\">%s</div></td>"
+                               "<td class=\"input\"><input type=\"button\" value=\"%s\" onclick=\"deleteWebApp('%s');\"></td>"
+                               "<td class=\"date\">%s <br /> %s</td></tr></tbody>",
+-                              app->id, app->icon_url, app->name, app->url, _("Delete"), app->id,
++                              html_encoded_id, encoded_icon_url, encoded_name, encoded_url, _("Delete"), js_encoded_id,
+                               /* Note for translators: this refers to the installation date. */
+-                              _("Installed on:"), app->install_date);
++                              _("Installed on:"), encoded_install_date);
+     }
+ 
+     g_string_append (data_str, "</table></div></body></html>");
+@@ -407,7 +426,9 @@ history_service_query_urls_cb (EphyHisto
+     EphyHistoryURL *url = (EphyHistoryURL *)l->data;
+     const char *snapshot;
+     g_autofree char *thumbnail_style = NULL;
+-    g_autofree char *markup = NULL;
++    g_autofree char *entity_encoded_title = NULL;
++    g_autofree char *attribute_encoded_title = NULL;
++    g_autofree char *encoded_url = NULL;
+ 
+     snapshot = ephy_snapshot_service_lookup_cached_snapshot_path (snapshot_service, url->url);
+     if (snapshot)
+@@ -415,15 +436,19 @@ history_service_query_urls_cb (EphyHisto
+     else
+       ephy_embed_shell_schedule_thumbnail_update (shell, url);
+ 
+-    markup = g_markup_escape_text (url->title, -1);
++    /* Title and URL are controlled by web content and could be malicious. */
++    entity_encoded_title = ephy_encode_for_html_entity (url->title);
++    attribute_encoded_title = ephy_encode_for_html_attribute (url->title);
++    encoded_url = ephy_encode_for_html_attribute (url->url);
+     g_string_append_printf (data_str,
+                             "<a class=\"overview-item\" title=\"%s\" href=\"%s\">"
+                             "  <div class=\"overview-close-button\" title=\"%s\"></div>"
+                             "  <span class=\"overview-thumbnail\"%s></span>"
+                             "  <span class=\"overview-title\">%s</span>"
+                             "</a>",
+-                            markup, url->url, _("Remove from overview"),
+-                            thumbnail_style ? thumbnail_style : "", url->title);
++                            attribute_encoded_title, encoded_url, _("Remove from overview"),
++                            thumbnail_style ? thumbnail_style : "",
++                            entity_encoded_title);
+   }
+ 
+   data_str = g_string_append (data_str,
+Index: epiphany-browser/embed/ephy-pdf-handler.c
+===================================================================
+--- epiphany-browser.orig/embed/ephy-pdf-handler.c
++++ epiphany-browser/embed/ephy-pdf-handler.c
+@@ -23,6 +23,7 @@
+ 
+ #include "ephy-embed-container.h"
+ #include "ephy-embed-shell.h"
++#include "ephy-output-encoding.h"
+ #include "ephy-web-view.h"
+ 
+ #include <gio/gio.h>
+@@ -124,8 +125,9 @@ pdf_file_loaded (GObject      *source,
+   GBytes *html_file;
+   g_autoptr (GError) error = NULL;
+   g_autoptr (GString) html = NULL;
+-  g_autofree gchar *b64 = NULL;
+   g_autofree char *file_data = NULL;
++  g_autofree char *encoded_file_data = NULL;
++  g_autofree char *encoded_filename = NULL;
+   gsize len = 0;
+ 
+   if (!g_file_load_contents_finish (G_FILE (source), res, &file_data, &len, NULL, &error)) {
+@@ -134,13 +136,13 @@ pdf_file_loaded (GObject      *source,
+     return;
+   }
+ 
+-  html_file = g_resources_lookup_data ("/org/gnome/epiphany/pdfjs/web/viewer.html", 0, NULL);
+-
+-  b64 = g_base64_encode ((const guchar *)file_data, len);
+   g_file_delete_async (G_FILE (source), G_PRIORITY_DEFAULT, NULL, pdf_file_deleted, NULL);
+ 
+-  html = g_string_new ("");
+-  g_string_printf (html, g_bytes_get_data (html_file, NULL), b64, self->file_name ? self->file_name : "");
++  html = g_string_new (NULL);
++  html_file = g_resources_lookup_data ("/org/gnome/epiphany/pdfjs/web/viewer.html", 0, NULL);
++  encoded_file_data = g_base64_encode ((const guchar *)file_data, len);
++  encoded_filename = self->file_name ? ephy_encode_for_html_attribute (self->file_name) : g_strdup ("");
++  g_string_printf (html, g_bytes_get_data (html_file, NULL), encoded_file_data, encoded_filename);
+ 
+   finish_uri_scheme_request (self, g_strdup (html->str), NULL);
+ }
+Index: epiphany-browser/embed/ephy-reader-handler.c
+===================================================================
+--- epiphany-browser.orig/embed/ephy-reader-handler.c
++++ epiphany-browser/embed/ephy-reader-handler.c
+@@ -24,6 +24,7 @@
+ #include "ephy-embed-container.h"
+ #include "ephy-embed-shell.h"
+ #include "ephy-lib-type-builtins.h"
++#include "ephy-output-encoding.h"
+ #include "ephy-settings.h"
+ #include "ephy-web-view.h"
+ 
+@@ -156,7 +157,9 @@ readability_js_finish_cb (GObject      *
+   g_autoptr (WebKitJavascriptResult) js_result = NULL;
+   g_autoptr (GError) error = NULL;
+   g_autofree gchar *byline = NULL;
++  g_autofree gchar *encoded_byline = NULL;
+   g_autofree gchar *content = NULL;
++  g_autofree gchar *encoded_title = NULL;
+   g_autoptr (GString) html = NULL;
+   g_autoptr (GBytes) style_css = NULL;
+   const gchar *title;
+@@ -173,10 +176,14 @@ readability_js_finish_cb (GObject      *
+ 
+   byline = readability_get_property_string (js_result, "byline");
+   content = readability_get_property_string (js_result, "content");
++  title = webkit_web_view_get_title (web_view);
++
++  encoded_byline = byline ? ephy_encode_for_html_entity (byline) : g_strdup ("");
++  encoded_title = ephy_encode_for_html_entity (title);
+ 
+-  html = g_string_new ("");
++  html = g_string_new (NULL);
+   style_css = g_resources_lookup_data ("/org/gnome/epiphany/readability/reader.css", G_RESOURCE_LOOKUP_FLAGS_NONE, NULL);
+-  title = webkit_web_view_get_title (web_view);
++
+   font_style = enum_nick (EPHY_TYPE_PREFS_READER_FONT_STYLE,
+                           g_settings_get_enum (EPHY_SETTINGS_READER,
+                                                EPHY_PREFS_READER_FONT_STYLE));
+@@ -186,7 +193,8 @@ readability_js_finish_cb (GObject      *
+ 
+   g_string_append_printf (html, "<style>%s</style>"
+                           "<title>%s</title>"
+-                          "<meta http-equiv=\"Content-Type\" content=\"text/html;\" charset=\"UTF-8\">" \
++                          "<meta http-equiv='Content-Type' content='text/html;' charset='UTF-8'>" \
++                          "<meta http-equiv='Content-Security-Policy' content=\"script-src 'none'\">" \
+                           "<body class='%s %s'>"
+                           "<article>"
+                           "<h2>"
+@@ -197,13 +205,27 @@ readability_js_finish_cb (GObject      *
+                           "</i>"
+                           "<hr>",
+                           (gchar *)g_bytes_get_data (style_css, NULL),
+-                          title,
++                          encoded_title,
+                           font_style,
+                           color_scheme,
+-                          title,
+-                          byline != NULL ? byline : "");
++                          encoded_title,
++                          encoded_byline);
++
++  /* We cannot encode the page content because it contains HTML tags inserted by
++   * Readability.js. Upstream recommends that we use an XSS sanitizer like
++   * DOMPurify plus Content-Security-Policy, but I'm not keen on adding more
++   * bundled JS dependencies, and we have an advantage over Firefox in that we
++   * don't need scripts to work at this point. So instead the above CSP
++   * completely blocks all scripts, which should hopefully obviate the need for
++   * a DOM purifier.
++   *
++   * Note the encoding for page title and byline is still required, as they're
++   * not supposed to contain markup, and Readability.js unescapes them before
++   * returning them to us.
++   */
+   g_string_append (html, content);
+   g_string_append (html, "</article>");
++  g_string_append (html, "</body>");
+ 
+   finish_uri_scheme_request (request, g_strdup (html->str), NULL);
+ }
+Index: epiphany-browser/embed/ephy-view-source-handler.c
+===================================================================
+--- epiphany-browser.orig/embed/ephy-view-source-handler.c
++++ epiphany-browser/embed/ephy-view-source-handler.c
+@@ -23,6 +23,7 @@
+ 
+ #include "ephy-embed-container.h"
+ #include "ephy-embed-shell.h"
++#include "ephy-output-encoding.h"
+ #include "ephy-web-view.h"
+ 
+ #include <gio/gio.h>
+@@ -109,7 +110,9 @@ web_resource_data_cb (WebKitWebResource
+                       EphyViewSourceRequest *request)
+ {
+   g_autofree guchar *data = NULL;
+-  g_autofree char *escaped_str = NULL;
++  g_autofree char *data_str = NULL;
++  g_autofree char *encoded_str = NULL;
++  g_autofree char *encoded_uri = NULL;
+   g_autoptr (GError) error = NULL;
+   g_autofree char *html = NULL;
+   gsize length;
+@@ -120,8 +123,13 @@ web_resource_data_cb (WebKitWebResource
+     return;
+   }
+ 
+-  /* Warning: data is not a string, so we pass length here because it's not NUL-terminated. */
+-  escaped_str = g_markup_escape_text ((const char *)data, length);
++  /* Convert data to a string */
++  data_str = g_malloc (length + 1);
++  memcpy (data_str, data, length);
++  data_str[length] = '\0';
++
++  encoded_str = ephy_encode_for_html_entity (data_str);
++  encoded_uri = ephy_encode_for_html_entity (webkit_web_resource_get_uri (resource));
+ 
+   html = g_strdup_printf ("<head>"
+                           "  <link rel='stylesheet' href='ephy-resource:///org/gnome/epiphany/highlightjs/nnfx.css' media='(prefers-color-scheme: no-preference), (prefers-color-scheme: light)'>"
+@@ -136,8 +144,8 @@ web_resource_data_cb (WebKitWebResource
+                           "          hljs.initLineNumbersOnLoad();</script>"
+                           "  <pre><code class='html'>%s</code></pre>"
+                           "</body>",
+-                          webkit_web_resource_get_uri (resource),
+-                          escaped_str);
++                          encoded_uri,
++                          encoded_str);
+ 
+   finish_uri_scheme_request (request, g_steal_pointer (&html), NULL);
+ }
+Index: epiphany-browser/embed/ephy-web-view.c
+===================================================================
+--- epiphany-browser.orig/embed/ephy-web-view.c
++++ epiphany-browser/embed/ephy-web-view.c
+@@ -38,6 +38,7 @@
+ #include "ephy-gsb-utils.h"
+ #include "ephy-history-service.h"
+ #include "ephy-lib-type-builtins.h"
++#include "ephy-output-encoding.h"
+ #include "ephy-permissions-manager.h"
+ #include "ephy-prefs.h"
+ #include "ephy-reader-handler.h"
+@@ -1772,9 +1773,11 @@ format_network_error_page (const char  *
+                            const char **icon_name,
+                            const char **style)
+ {
+-  char *formatted_origin;
+-  char *formatted_reason;
+-  char *first_paragraph;
++  g_autofree char *encoded_uri = NULL;
++  g_autofree char *encoded_origin = NULL;
++  g_autofree char *formatted_origin = NULL;
++  g_autofree char *formatted_reason = NULL;
++  g_autofree char *first_paragraph = NULL;
+   const char *second_paragraph;
+ 
+   /* Page title when a site cannot be loaded due to a network error. */
+@@ -1783,7 +1786,8 @@ format_network_error_page (const char  *
+   /* Message title when a site cannot be loaded due to a network error. */
+   *message_title = g_strdup (_("Unable to display this website"));
+ 
+-  formatted_origin = g_strdup_printf ("<strong>%s</strong>", origin);
++  encoded_origin = ephy_encode_for_html_entity (origin);
++  formatted_origin = g_strdup_printf ("<strong>%s</strong>", encoded_origin);
+   /* Error details when a site cannot be loaded due to a network error. */
+   first_paragraph = g_strdup_printf (_("The site at %s seems to be "
+                                        "unavailable."),
+@@ -1805,16 +1809,13 @@ format_network_error_page (const char  *
+ 
+   /* The button on the network error page. DO NOT ADD MNEMONICS HERE. */
+   *button_label = g_strdup (_("Reload"));
+-  *button_action = g_strdup_printf ("window.location = '%s';", uri);
++  encoded_uri = ephy_encode_for_javascript (uri);
++  *button_action = g_strdup_printf ("window.location = '%s';", encoded_uri);
+   /* Mnemonic for the Reload button on browser error pages. */
+   *button_accesskey = C_("reload-access-key", "R");
+ 
+   *icon_name = "network-error-symbolic.svg";
+   *style = "default";
+-
+-  g_free (formatted_origin);
+-  g_free (formatted_reason);
+-  g_free (first_paragraph);
+ }
+ 
+ static void
+@@ -1828,10 +1829,12 @@ format_crash_error_page (const char  *ur
+                          const char **icon_name,
+                          const char **style)
+ {
+-  char *formatted_uri;
+-  char *formatted_distributor;
+-  char *first_paragraph;
+-  char *second_paragraph;
++  g_autofree char *html_encoded_uri = NULL;
++  g_autofree char *js_encoded_uri = NULL;
++  g_autofree char *formatted_uri = NULL;
++  g_autofree char *formatted_distributor = NULL;
++  g_autofree char *first_paragraph = NULL;
++  g_autofree char *second_paragraph = NULL;
+ 
+   /* Page title when a site cannot be loaded due to a page crash error. */
+   *page_title = g_strdup_printf (_("Problem Loading Page"));
+@@ -1839,7 +1842,8 @@ format_crash_error_page (const char  *ur
+   /* Message title when a site cannot be loaded due to a page crash error. */
+   *message_title = g_strdup (_("Oops! There may be a problem"));
+ 
+-  formatted_uri = g_strdup_printf ("<strong>%s</strong>", uri);
++  html_encoded_uri = ephy_encode_for_html_entity (uri);
++  formatted_uri = g_strdup_printf ("<strong>%s</strong>", html_encoded_uri);
+   /* Error details when a site cannot be loaded due to a page crash error. */
+   first_paragraph = g_strdup_printf (_("The page %s may have caused Web to "
+                                        "close unexpectedly."),
+@@ -1858,17 +1862,13 @@ format_crash_error_page (const char  *ur
+ 
+   /* The button on the page crash error page. DO NOT ADD MNEMONICS HERE. */
+   *button_label = g_strdup (_("Reload"));
+-  *button_action = g_strdup_printf ("window.location = '%s';", uri);
++  js_encoded_uri = ephy_encode_for_javascript (uri);
++  *button_action = g_strdup_printf ("window.location = '%s';", js_encoded_uri);
+   /* Mnemonic for the Reload button on browser error pages. */
+   *button_accesskey = C_("reload-access-key", "R");
+ 
+   *icon_name = "computer-fail-symbolic.svg";
+   *style = "default";
+-
+-  g_free (formatted_uri);
+-  g_free (formatted_distributor);
+-  g_free (first_paragraph);
+-  g_free (second_paragraph);
+ }
+ 
+ static void
+@@ -1882,6 +1882,7 @@ format_process_crash_error_page (const c
+                                  const char **icon_name,
+                                  const char **style)
+ {
++  g_autofree char *encoded_uri = NULL;
+   const char *first_paragraph;
+ 
+   /* Page title when a site cannot be loaded due to a process crash error. */
+@@ -1897,7 +1898,8 @@ format_process_crash_error_page (const c
+ 
+   /* The button on the process crash error page. DO NOT ADD MNEMONICS HERE. */
+   *button_label = g_strdup (_("Reload"));
+-  *button_action = g_strdup_printf ("window.location = '%s';", uri);
++  encoded_uri = ephy_encode_for_javascript (uri);
++  *button_action = g_strdup_printf ("window.location = '%s';", encoded_uri);
+   /* Mnemonic for the Reload button on browser error pages. */
+   *button_accesskey = C_("reload-access-key", "R");
+ 
+@@ -1921,8 +1923,9 @@ format_tls_error_page (EphyWebView  *vie
+                        const char  **icon_name,
+                        const char  **style)
+ {
+-  char *formatted_origin;
+-  char *first_paragraph;
++  g_autofree char *encoded_origin = NULL;
++  g_autofree char *formatted_origin = NULL;
++  g_autofree char *first_paragraph = NULL;
+ 
+   /* Page title when a site is not loaded due to an invalid TLS certificate. */
+   *page_title = g_strdup_printf (_("Security Violation"));
+@@ -1930,7 +1933,8 @@ format_tls_error_page (EphyWebView  *vie
+   /* Message title when a site is not loaded due to an invalid TLS certificate. */
+   *message_title = g_strdup (_("This Connection is Not Secure"));
+ 
+-  formatted_origin = g_strdup_printf ("<strong>%s</strong>", origin);
++  encoded_origin = ephy_encode_for_html_entity (origin);
++  formatted_origin = g_strdup_printf ("<strong>%s</strong>", encoded_origin);
+   /* Error details when a site is not loaded due to an invalid TLS certificate. */
+   first_paragraph = g_strdup_printf (_("This does not look like the real %s. "
+                                        "Attackers might be trying to steal or "
+@@ -1956,9 +1960,6 @@ format_tls_error_page (EphyWebView  *vie
+ 
+   *icon_name = "channel-insecure-symbolic.svg";
+   *style = "danger";
+-
+-  g_free (formatted_origin);
+-  g_free (first_paragraph);
+ }
+ 
+ static void
+@@ -1978,8 +1979,9 @@ format_unsafe_browsing_error_page (EphyW
+                                    const char  **icon_name,
+                                    const char  **style)
+ {
+-  char *formatted_origin;
+-  char *first_paragraph;
++  g_autofree char *encoded_origin = NULL;
++  g_autofree char *formatted_origin = NULL;
++  g_autofree char *first_paragraph = NULL;
+ 
+   /* Page title when a site is flagged by Google Safe Browsing verification. */
+   *page_title = g_strdup_printf (_("Security Warning"));
+@@ -1987,7 +1989,8 @@ format_unsafe_browsing_error_page (EphyW
+   /* Message title on the unsafe browsing error page. */
+   *message_title = g_strdup (_("Unsafe website detected!"));
+ 
+-  formatted_origin = g_strdup_printf ("<strong>%s</strong>", origin);
++  encoded_origin = ephy_encode_for_html_entity (origin);
++  formatted_origin = g_strdup_printf ("<strong>%s</strong>", encoded_origin);
+   /* Error details on the unsafe browsing error page.
+    * https://developers.google.com/safe-browsing/v4/usage-limits#UserWarnings
+    */
+@@ -2045,9 +2048,6 @@ format_unsafe_browsing_error_page (EphyW
+ 
+   *icon_name = "security-high-symbolic.svg";
+   *style = "danger";
+-
+-  g_free (formatted_origin);
+-  g_free (first_paragraph);
+ }
+ 
+ static void
+@@ -2061,7 +2061,8 @@ format_no_such_file_error_page (EphyWebV
+                                 const char  **icon_name,
+                                 const char  **style)
+ {
+-  g_autofree gchar *formatted_origin = NULL;
++  g_autofree gchar *encoded_address = NULL;
++  g_autofree gchar *formatted_address = NULL;
+   g_autofree gchar *first_paragraph = NULL;
+   g_autofree gchar *second_paragraph = NULL;
+ 
+@@ -2071,10 +2072,11 @@ format_no_such_file_error_page (EphyWebV
+   /* Message title on the no such file error page. */
+   *message_title = g_strdup (_("File not found"));
+ 
+-  formatted_origin = g_strdup_printf ("<strong>%s</strong>", view->address);
++  encoded_address = ephy_encode_for_html_entity (view->address);
++  formatted_address = g_strdup_printf ("<strong>%s</strong>", encoded_address);
+ 
+   first_paragraph = g_strdup_printf (_("%s could not be found."),
+-                                     formatted_origin);
++                                     formatted_address);
+   second_paragraph = g_strdup_printf (_("Please check the file name for "
+                                         "capitalization or other typing errors. Also check if "
+                                         "it has been moved, renamed, or deleted."));
+@@ -2109,19 +2111,19 @@ ephy_web_view_load_error_page (EphyWebVi
+                                GError               *error,
+                                gpointer              user_data)
+ {
+-  GBytes *html_file;
+-  GString *html = g_string_new ("");
+-  char *origin = NULL;
+-  char *lang = NULL;
+-  char *page_title = NULL;
+-  char *msg_title = NULL;
+-  char *msg_body = NULL;
+-  char *msg_details = NULL;
+-  char *button_label = NULL;
+-  char *hidden_button_label = NULL;
+-  char *button_action = NULL;
+-  char *hidden_button_action = NULL;
+-  char *style_sheet = NULL;
++  g_autoptr (GBytes) html_file = NULL;
++  g_autoptr (GString) html = g_string_new (NULL);
++  g_autofree char *origin = NULL;
++  g_autofree char *lang = NULL;
++  g_autofree char *page_title = NULL;
++  g_autofree char *msg_title = NULL;
++  g_autofree char *msg_body = NULL;
++  g_autofree char *msg_details = NULL;
++  g_autofree char *button_label = NULL;
++  g_autofree char *hidden_button_label = NULL;
++  g_autofree char *button_action = NULL;
++  g_autofree char *hidden_button_action = NULL;
++  g_autofree char *style_sheet = NULL;
+   const char *button_accesskey = NULL;
+   const char *hidden_button_accesskey = NULL;
+   const char *icon_name = NULL;
+@@ -2261,23 +2263,9 @@ ephy_web_view_load_error_page (EphyWebVi
+                    button_accesskey, button_label);
+ #pragma GCC diagnostic pop
+ 
+-  g_bytes_unref (html_file);
+-  g_free (origin);
+-  g_free (lang);
+-  g_free (page_title);
+-  g_free (msg_title);
+-  g_free (msg_body);
+-  g_free (msg_details);
+-  g_free (button_label);
+-  g_free (button_action);
+-  g_free (hidden_button_label);
+-  g_free (hidden_button_action);
+-  g_free (style_sheet);
+-
+   /* Make our history backend ignore the next page load, since it will be an error page. */
+   ephy_web_view_freeze_history (view);
+   webkit_web_view_load_alternate_html (WEBKIT_WEB_VIEW (view), html->str, uri, 0);
+-  g_string_free (html, TRUE);
+ }
+ 
+ static gboolean
+Index: epiphany-browser/lib/ephy-output-encoding.c
+===================================================================
+--- /dev/null
++++ epiphany-browser/lib/ephy-output-encoding.c
+@@ -0,0 +1,117 @@
++/* -*- Mode: C; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
++/*
++ *  Copyright © Red Hat Inc.
++ *
++ *  This file is part of Epiphany.
++ *
++ *  Epiphany is free software: you can redistribute it and/or modify
++ *  it under the terms of the GNU General Public License as published by
++ *  the Free Software Foundation, either version 3 of the License, or
++ *  (at your option) any later version.
++ *
++ *  Epiphany is distributed in the hope that it will be useful,
++ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
++ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
++ *  GNU General Public License for more details.
++ *
++ *  You should have received a copy of the GNU General Public License
++ *  along with Epiphany.  If not, see <http://www.gnu.org/licenses/>.
++ */
++
++#include "config.h"
++#include "ephy-output-encoding.h"
++
++#include <glib.h>
++
++#if !GLIB_CHECK_VERSION(2, 68, 0)
++static guint
++g_string_replace (GString     *string,
++                  const gchar *find,
++                  const gchar *replace,
++                  guint        limit)
++{
++  gsize f_len, r_len, pos;
++  gchar *cur, *next;
++  guint n = 0;
++
++  g_return_val_if_fail (string != NULL, 0);
++  g_return_val_if_fail (find != NULL, 0);
++  g_return_val_if_fail (replace != NULL, 0);
++
++  f_len = strlen (find);
++  r_len = strlen (replace);
++  cur = string->str;
++
++  while ((next = strstr (cur, find)) != NULL)
++    {
++      pos = next - string->str;
++      g_string_erase (string, pos, f_len);
++      g_string_insert (string, pos, replace);
++      cur = string->str + pos + r_len;
++      n++;
++      /* Only match the empty string once at any given position, to
++       * avoid infinite loops */
++      if (f_len == 0)
++        {
++          if (cur[0] == '\0')
++            break;
++          else
++            cur++;
++        }
++      if (n == limit)
++        break;
++    }
++
++  return n;
++}
++#endif
++
++char *
++ephy_encode_for_html_entity (const char *input)
++{
++  GString *str = g_string_new (input);
++
++  g_string_replace (str, "&", "&amp;", 0);
++  g_string_replace (str, "<", "&lt;", 0);
++  g_string_replace (str, ">", "&gt;", 0);
++  g_string_replace (str, "\"", "&quot;", 0);
++  g_string_replace (str, "'", "&#x27;", 0);
++  g_string_replace (str, "/", "&#x2F;", 0);
++
++  return g_string_free (str, FALSE);
++}
++
++static char *
++encode_all_except_alnum (const char *input,
++                         const char *format)
++{
++  GString *str;
++  const char *c = input;
++
++  if (!g_utf8_validate (input, -1, NULL))
++    return g_strdup ("");
++
++  str = g_string_new (NULL);
++  do {
++    gunichar u = g_utf8_get_char (c);
++    if (g_unichar_isalnum (u))
++      g_string_append_unichar (str, u);
++    else
++      g_string_append_printf (str, format, u);
++    c = g_utf8_next_char (c);
++  } while (*c);
++
++  return g_string_free (str, FALSE);
++}
++
++char *
++ephy_encode_for_html_attribute (const char *input)
++{
++  return encode_all_except_alnum (input, "&#x%02x;");
++}
++
++char *
++ephy_encode_for_javascript (const char *input)
++{
++  return encode_all_except_alnum (input, "\\u%04u;");
++}
+Index: epiphany-browser/lib/ephy-output-encoding.h
+===================================================================
+--- /dev/null
++++ epiphany-browser/lib/ephy-output-encoding.h
+@@ -0,0 +1,38 @@
++/* -*- Mode: C; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
++/*
++ *  Copyright © 2021 Red Hat Inc.
++ *
++ *  This file is part of Epiphany.
++ *
++ *  Epiphany is free software: you can redistribute it and/or modify
++ *  it under the terms of the GNU General Public License as published by
++ *  the Free Software Foundation, either version 3 of the License, or
++ *  (at your option) any later version.
++ *
++ *  Epiphany is distributed in the hope that it will be useful,
++ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
++ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
++ *  GNU General Public License for more details.
++ *
++ *  You should have received a copy of the GNU General Public License
++ *  along with Epiphany.  If not, see <http://www.gnu.org/licenses/>.
++ */
++
++#pragma once
++
++#include <glib.h>
++
++G_BEGIN_DECLS
++
++/* These functions implement the OWASP XSS prevention output encoding rules:
++ * https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html#output-encoding-rules-summary
++ *
++ * You must *carefully* read that document to safely inject untrusted data into
++ * web content. Here be dragons.
++ */
++
++char *ephy_encode_for_html_entity    (const char *input);
++char *ephy_encode_for_html_attribute (const char *input);
++char *ephy_encode_for_javascript     (const char *input);
++
++G_END_DECLS
+Index: epiphany-browser/lib/meson.build
+===================================================================
+--- epiphany-browser.orig/lib/meson.build
++++ epiphany-browser/lib/meson.build
+@@ -21,6 +21,7 @@ libephymisc_sources = [
+   'ephy-langs.c',
+   'ephy-notification.c',
+   'ephy-notification-container.c',
++  'ephy-output-encoding.c',
+   'ephy-permissions-manager.c',
+   'ephy-profile-utils.c',
+   'ephy-search-engine-manager.c',