Security - Hardening XML parser against XXE

changedetectionio/html_tools.py

@@ -282,7 +282,7 @@ def xpath_filter(xpath_filter, html_content, append_pretty_line_formatting=False
     try:
         if is_xml:
             # So that we can keep CDATA for cdata_in_document_to_text() to process
-            parser = etree.XMLParser(strip_cdata=False)
+            parser = etree.XMLParser(strip_cdata=False, resolve_entities=False, no_network=True)
             # For XML/RSS content, use etree.fromstring to properly handle XML declarations
             tree = etree.fromstring(html_content.encode('utf-8') if isinstance(html_content, str) else html_content, parser=parser)
         else:
@@ -346,7 +346,7 @@ def xpath1_filter(xpath_filter, html_content, append_pretty_line_formatting=Fals
     try:
         if is_xml:
             # So that we can keep CDATA for cdata_in_document_to_text() to process
-            parser = etree.XMLParser(strip_cdata=False)
+            parser = etree.XMLParser(strip_cdata=False, resolve_entities=False, no_network=True)
             # For XML/RSS content, use etree.fromstring to properly handle XML declarations
             tree = etree.fromstring(html_content.encode('utf-8') if isinstance(html_content, str) else html_content, parser=parser)
         else:

changedetectionio/tests/unit/test_xml_security.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python3
+
+# run from dir above changedetectionio/ dir
+# python3 -m pytest changedetectionio/tests/unit/test_xml_security.py
+
+import pytest
+from changedetectionio import html_tools
+
+
+def _xxe_payload(file_path: str) -> str:
+    return f"""<?xml version="1.0"?>
+<!DOCTYPE root [
+  <!ENTITY xxe SYSTEM "file://{file_path}">
+]>
+<root><item>&xxe;</item></root>"""
+
+
+def test_xxe_not_expanded_xpath_filter(tmp_path):
+    """xpath_filter must not expand external entities (CVE-2026-41895)."""
+    sentinel_file = tmp_path / "sentinel.txt"
+    sentinel = "xxe_sentinel_should_never_appear_in_output"
+    sentinel_file.write_text(sentinel)
+
+    result = html_tools.xpath_filter("//item", _xxe_payload(sentinel_file), is_xml=True)
+    assert sentinel not in result
+
+
+def test_xxe_not_expanded_xpath1_filter(tmp_path):
+    """xpath1_filter must not expand external entities (CVE-2026-41895)."""
+    sentinel_file = tmp_path / "sentinel.txt"
+    sentinel = "xxe_sentinel_should_never_appear_in_output"
+    sentinel_file.write_text(sentinel)
+
+    result = html_tools.xpath1_filter("//item", _xxe_payload(sentinel_file), is_xml=True)
+    assert sentinel not in result