sources/saml: validate SAMLResponse signature

passbook/sources/saml/api.py

@@ -13,7 +13,7 @@ class SAMLSourceSerializer(ModelSerializer):
         model = SAMLSource
         fields = [
             "pk",
-            "entity_id",
+            "issuer",
             "idp_url",
             "idp_logout_url",
             "auto_logout",

passbook/sources/saml/exceptions.py

@@ -0,0 +1,9 @@
+"""passbook saml source exceptions"""
+
+
+class MissingSAMLResponse(Exception):
+    """Exception raised when request does not contain SAML Response."""
+
+
+class UnsupportedNameIDFormat(Exception):
+    """Exception raised when SAML Response contains NameID Format not supported."""

passbook/sources/saml/forms.py

@@ -22,7 +22,7 @@ class SAMLSourceForm(forms.ModelForm):
 
         model = SAMLSource
         fields = SOURCE_FORM_FIELDS + [
-            "entity_id",
+            "issuer",
             "idp_url",
             "idp_logout_url",
             "auto_logout",
@@ -31,7 +31,7 @@ class SAMLSourceForm(forms.ModelForm):
         widgets = {
             "name": forms.TextInput(),
             "policies": FilteredSelectMultiple(_("policies"), False),
-            "entity_id": forms.TextInput(),
+            "issuer": forms.TextInput(),
             "idp_url": forms.TextInput(),
             "idp_logout_url": forms.TextInput(),
         }

passbook/sources/saml/processors/base.py

@@ -0,0 +1,85 @@
+"""passbook saml source processor"""
+from typing import Optional
+from xml.etree.ElementTree import Element
+
+from defusedxml import ElementTree
+from django.http import HttpRequest
+from signxml import XMLVerifier
+from structlog import get_logger
+
+from passbook.core.models import User
+from passbook.providers.saml.utils.encoding import decode_base64_and_inflate
+from passbook.sources.saml.exceptions import (
+    MissingSAMLResponse,
+    UnsupportedNameIDFormat,
+)
+from passbook.sources.saml.models import SAMLSource
+
+LOGGER = get_logger()
+
+
+class Processor:
+    """SAML Response Processor"""
+
+    _source: SAMLSource
+
+    _root: Element
+    _root_xml: str
+
+    def __init__(self, source: SAMLSource):
+        self._source = source
+
+    def parse(self, request: HttpRequest):
+        """Check if `request` contains SAML Response data, parse and validate it."""
+        # First off, check if we have any SAML Data at all.
+        raw_response = request.POST.get("SAMLResponse", None)
+        if not raw_response:
+            raise MissingSAMLResponse("Request does not contain 'SAMLResponse'")
+        # relay_state = request.POST.get('RelayState', None)
+        # Check if response is compressed, b64 decode it
+        self._root_xml = response = decode_base64_and_inflate(raw_response)
+        self._root = ElementTree.fromstring(self._root_xml)
+        # Verify signed XML
+        self._verify_signed()
+
+    def _verify_signed(self):
+        """Verify SAML Response's Signature"""
+        verifier = XMLVerifier()
+        verifier.verify(self._root_xml, x509_cert=self._source.signing_cert)
+
+    def _get_email(self) -> Optional[str]:
+        """
+        Returns the email out of the response.
+
+        At present, response must pass the email address as the Subject, eg.:
+
+        <saml:Subject>
+                <saml:NameID Format="urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress"
+                            SPNameQualifier=""
+                            >email@example.com</saml:NameID>
+        """
+        assertion = self._root.find("{urn:oasis:names:tc:SAML:2.0:assertion}Assertion")
+        subject = assertion.find("{urn:oasis:names:tc:SAML:2.0:assertion}Subject")
+        name_id = subject.find("{urn:oasis:names:tc:SAML:2.0:assertion}NameID")
+        name_id_format = name_id.attrib["Format"]
+        if name_id_format != "urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress":
+            raise UnsupportedNameIDFormat(
+                f"Assertion contains NameID with unsupported format {name_id_format}."
+            )
+        return name_id.text
+
+    def get_user(self) -> User:
+        """
+        Gets info out of the response and locally logs in this user.
+        May create a local user account first.
+        Returns the user object that was created.
+        """
+        email = self._get_email()
+        try:
+            user = User.objects.get(email=email)
+        except User.DoesNotExist:
+            user = User.objects.create_user(username=email, email=email)
+            # TODO: Property Mappings
+            user.set_unusable_password()
+            user.save()
+        return user

passbook/sources/saml/utils.py

@@ -2,7 +2,6 @@
 from django.http import HttpRequest
 from django.shortcuts import reverse
 
-from passbook.core.models import User
 from passbook.sources.saml.models import SAMLSource
 
 
@@ -19,65 +18,3 @@ def build_full_url(view: str, request: HttpRequest, source: SAMLSource) -> str:
     return request.build_absolute_uri(
         reverse(f"passbook_sources_saml:{view}", kwargs={"source_slug": source.slug})
     )
-
-
-def _get_email_from_response(root):
-    """
-    Returns the email out of the response.
-
-    At present, response must pass the email address as the Subject, eg.:
-
-    <saml:Subject>
-            <saml:NameID Format="urn:oasis:names:tc:SAML:2.0:nameid-format:email"
-                         SPNameQualifier=""
-                         >email@example.com</saml:NameID>
-    """
-    assertion = root.find("{urn:oasis:names:tc:SAML:2.0:assertion}Assertion")
-    subject = assertion.find("{urn:oasis:names:tc:SAML:2.0:assertion}Subject")
-    name_id = subject.find("{urn:oasis:names:tc:SAML:2.0:assertion}NameID")
-    return name_id.text
-
-
-def _get_attributes_from_response(root):
-    """
-    Returns the SAML Attributes (if any) that are present in the response.
-
-    NOTE: Technically, attribute values could be any XML structure.
-          But for now, just assume a single string value.
-    """
-    flat_attributes = {}
-    assertion = root.find("{urn:oasis:names:tc:SAML:2.0:assertion}Assertion")
-    attributes = assertion.find(
-        "{urn:oasis:names:tc:SAML:2.0:assertion}AttributeStatement"
-    )
-    for attribute in attributes.getchildren():
-        name = attribute.attrib.get("Name")
-        children = attribute.getchildren()
-        if not children:
-            # Ignore empty-valued attributes. (I think these are not allowed.)
-            continue
-        if len(children) == 1:
-            # See NOTE:
-            flat_attributes[name] = children[0].text
-        else:
-            # It has multiple values.
-            for child in children:
-                # See NOTE:
-                flat_attributes.setdefault(name, []).append(child.text)
-    return flat_attributes
-
-
-def _get_user_from_response(root):
-    """
-    Gets info out of the response and locally logs in this user.
-    May create a local user account first.
-    Returns the user object that was created.
-    """
-    email = _get_email_from_response(root)
-    try:
-        user = User.objects.get(email=email)
-    except User.DoesNotExist:
-        user = User.objects.create_user(username=email, email=email)
-        user.set_unusable_password()
-        user.save()
-    return user

passbook/sources/saml/views.py

@@ -1,7 +1,4 @@
 """saml sp views"""
-import base64
-
-from defusedxml import ElementTree
 from django.contrib.auth import login, logout
 from django.http import Http404, HttpRequest, HttpResponse
 from django.shortcuts import get_object_or_404, redirect, render, reverse
@@ -10,15 +7,17 @@ from django.views import View
 from django.views.decorators.csrf import csrf_exempt
 from signxml.util import strip_pem_header
 
+from passbook.lib.views import bad_request_message
 from passbook.providers.saml.utils import get_random_id, render_xml
 from passbook.providers.saml.utils.encoding import nice64
 from passbook.providers.saml.utils.time import get_time_string
-from passbook.sources.saml.models import SAMLSource
-from passbook.sources.saml.utils import (
-    _get_user_from_response,
-    build_full_url,
-    get_issuer,
+from passbook.sources.saml.exceptions import (
+    MissingSAMLResponse,
+    UnsupportedNameIDFormat,
 )
+from passbook.sources.saml.models import SAMLSource
+from passbook.sources.saml.processors.base import Processor
+from passbook.sources.saml.utils import build_full_url, get_issuer
 from passbook.sources.saml.xml_render import get_authnrequest_xml
 
 
@@ -62,14 +61,18 @@ class ACSView(View):
         source: SAMLSource = get_object_or_404(SAMLSource, slug=source_slug)
         if not source.enabled:
             raise Http404
-        # sso_session = request.POST.get('RelayState', None)
-        data = request.POST.get("SAMLResponse", None)
-        response = base64.b64decode(data)
-        root = ElementTree.fromstring(response)
-        user = _get_user_from_response(root)
-        # attributes = _get_attributes_from_response(root)
-        login(request, user, backend="django.contrib.auth.backends.ModelBackend")
-        return redirect(reverse("passbook_core:overview"))
+        processor = Processor(source)
+        try:
+            processor.parse(request)
+        except MissingSAMLResponse as exc:
+            return bad_request_message(request, str(exc))
+
+        try:
+            user = processor.get_user()
+            login(request, user, backend="django.contrib.auth.backends.ModelBackend")
+            return redirect(reverse("passbook_core:overview"))
+        except UnsupportedNameIDFormat as exc:
+            return bad_request_message(request, str(exc))
 
 
 class SLOView(View):