From a08847ab39bb512d500cf196981a3e8780c83600 Mon Sep 17 00:00:00 2001
From: "Christoph M. Becker" <cmbecker69@gmx.de>
Date: Mon, 15 Mar 2021 10:26:50 +0100
Subject: Fix #66783: UAF when appending DOMDocument to element

According to the DOM standard, elements may only contain element, text,
processing instruction and comment nodes[1].  It is also specified that
a HierarchyRequestError should be thrown if a document is to be
inserted[2].  We follow that standard, and prevent the use-after-free
this way.

[1] <https://dom.spec.whatwg.org/#node-trees>
[2] <https://dom.spec.whatwg.org/#mutation-algorithms>

Closes GH-6765.
---
 NEWS                        |  2 ++
 ext/dom/php_dom.c           | 10 +++++++---
 ext/dom/tests/bug66783.phpt | 19 +++++++++++++++++++
 3 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 ext/dom/tests/bug66783.phpt

diff --git a/NEWS b/NEWS
index 2b7c2f91be..0584f6504c 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,8 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? 2021, PHP 7.4.18
 
+- DOM:
+  . Fixed bug #66783 (UAF when appending DOMDocument to element). (cmb)
 
 01 Apr 2021, PHP 7.4.17
 
diff --git a/ext/dom/php_dom.c b/ext/dom/php_dom.c
index 6bc72e9f97..2f2878d5e1 100644
--- a/ext/dom/php_dom.c
+++ b/ext/dom/php_dom.c
@@ -1302,9 +1302,13 @@ int dom_hierarchy(xmlNodePtr parent, xmlNodePtr child)
 {
 	xmlNodePtr nodep;
 
-    if (parent == NULL || child == NULL || child->doc != parent->doc) {
-        return SUCCESS;
-    }
+	if (parent == NULL || child == NULL || child->doc != parent->doc) {
+		return SUCCESS;
+	}
+
+	if (child->type == XML_DOCUMENT_NODE) {
+		return FAILURE;
+	}
 
 	nodep = parent;
 
diff --git a/ext/dom/tests/bug66783.phpt b/ext/dom/tests/bug66783.phpt
new file mode 100644
index 0000000000..98981a88f6
--- /dev/null
+++ b/ext/dom/tests/bug66783.phpt
@@ -0,0 +1,19 @@
+--TEST--
+Bug #66783 (UAF when appending DOMDocument to element)
+--SKIPIF--
+<?php
+if (!extension_loaded('dom')) die('skip dom extension not available');
+?>
+--FILE--
+<?php
+$doc = new DomDocument;
+$doc->loadXML('<root></root>');
+$e = $doc->createElement('e');
+try {
+    $e->appendChild($doc);
+} catch (DOMException $ex) {
+    echo $ex->getMessage(), PHP_EOL;
+}
+?>
+--EXPECTF--
+Hierarchy Request Error
-- 
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