fix(security): use defusedxml for untrusted XML parsing (#259)

Detected by Aeon + Semgrep (5x use-defused-xml ERROR).
Severity: medium
CWE-776 (billion laughs) / CWE-611 (XML external entity)

Five XML parse sites pass response bodies into the Python stdlib
xml.etree.ElementTree without protection against entity expansion
attacks. Python's ElementTree still permits internal entity references
by default (per the docs vulnerabilities table), so a malicious or
compromised upstream can ship a "billion laughs"-style payload that
expands to gigabytes in memory.

The user-controllable site is sb_monitor._parse_rss: the OpenClaw skill
exposes add_custom_feed(name, url, ...) to the agent, then
poll_custom_feeds fetches feed.url and passes the body to
xml.etree.ElementTree.fromstring with no host allowlist or
entity-bomb defence. The other four sites (psk_reporter_fetcher,
aircraft_database, cctv_pipeline x2) parse XML from hard-coded
upstreams (pskreporter.info, s3.opensky-network.org,
datos.madrid.es); defence-in-depth for upstream-compromise/MITM.

Switch all five call sites to defusedxml.ElementTree. Same
fromstring/find/findall/iter/findtext API, but rejects entity
references by default (raises defusedxml.EntitiesForbidden).
Confirmed locally that a 4-deep billion-laughs payload that
expands to 3000 chars under stdlib ET is rejected by defusedxml.

Added defusedxml>=0.7.1 to backend/pyproject.toml dependencies.

Co-authored-by: aeonframework <aeon-bot@aaronjmars.com>

backend/pyproject.toml

@@ -15,6 +15,7 @@ dependencies = [
     "cachetools==5.5.2",
     "cloudscraper==1.2.71",
     "cryptography>=41.0.0",
+    "defusedxml>=0.7.1",
     "fastapi==0.115.12",
     "feedparser==6.0.10",
     "httpx==0.28.1",

backend/services/cctv_pipeline.py

@@ -987,7 +987,7 @@ _KML_NS = {"kml": "http://www.opengis.net/kml/2.2"}
 
 def _find_kml_element(element, tag):
     """Find first descendant matching tag, ignoring XML namespace prefix."""
-    import xml.etree.ElementTree as ET
+    import defusedxml.ElementTree as ET
     el = element.find(f".//{tag}")
     if el is not None:
         return el
@@ -1015,7 +1015,7 @@ class MadridCityIngestor(BaseCCTVIngestor):
     KML_URL = "http://datos.madrid.es/egob/catalogo/202088-0-trafico-camaras.kml"
 
     def fetch_data(self) -> List[Dict[str, Any]]:
-        import xml.etree.ElementTree as ET
+        import defusedxml.ElementTree as ET
 
         try:
             response = fetch_with_curl(self.KML_URL, timeout=20)

backend/services/fetchers/aircraft_database.py

@@ -16,9 +16,9 @@ import csv
 import logging
 import threading
 import time
-import xml.etree.ElementTree as ET
 from typing import Any
 
+import defusedxml.ElementTree as ET
 import requests
 
 logger = logging.getLogger(__name__)

backend/services/psk_reporter_fetcher.py

@@ -6,8 +6,8 @@ Docs: https://pskreporter.info/pskdev.html
 """
 
 import logging
-import xml.etree.ElementTree as ET
 
+import defusedxml.ElementTree as ET
 import requests
 from cachetools import TTLCache, cached
 

openclaw-skills/shadowbroker/sb_monitor.py

@@ -701,7 +701,7 @@ async def _fetch_feed(feed: CustomFeed) -> list[dict]:
 
 def _parse_rss(xml_text: str, feed: CustomFeed) -> list[dict]:
     """Parse an RSS/Atom feed into normalized items."""
-    import xml.etree.ElementTree as ET
+    import defusedxml.ElementTree as ET
 
     items = []
     try: