use subresource integrity attributes to guard against CDNs being used as an attack vector; drop external resources that we can't protect this way (fonts); fixes #234

tools/update-subresource-integrity.py

@@ -0,0 +1,24 @@
+#!/usr/bin/python3
+# Updates subresource integrity attributes in management/templates/index.html
+# to prevent CDN-hosted resources from being used as an attack vector. Run this
+# after updating the Bootstrap and jQuery <link> and <script> to compute the
+# appropriate hash and insert it into the template.
+
+import re, urllib.request, hashlib, base64
+
+fn = "management/templates/index.html"
+
+with open(fn, 'r') as f:
+	content = f.read()
+
+def make_integrity(url):
+	resource = urllib.request.urlopen(url).read()
+	return "sha256-" + base64.b64encode(hashlib.sha256(resource).digest()).decode('ascii')
+
+content = re.sub(
+	r'<(link rel="stylesheet" href|script src)="(.*?)" integrity="(.*?)"',
+	lambda m : '<' + m.group(1) + '="' + m.group(2) + '" integrity="' + make_integrity(m.group(2)) + '"',
+	content)
+
+with open(fn, 'w') as f:
+	f.write(content)