Fix CVE-2021-21238 - SAML XML Signature wrapping

All users of pysaml2 that use the default `CryptoBackendXmlSec1` backend and need to
verify signed SAML documents are impacted. `pysaml2 <= 6.4.1` does not validate the SAML
document against an XML schema. This allows invalid XML documents to trick the
verification process, by presenting elements with a valid signature inside elements
whose content has been malformed. The verification is offloaded to `xmlsec1` and
`xmlsec1` will not validate every signature in the given document, but only the first it
finds in the given scope.

Credits for the report:

- Victor Schönfelder Garcia (isits AG International School of IT Security)
- Juraj Somorovsky (Paderborn University)
- Vladislav Mladenov (Ruhr University Bochum)

Signed-off-by: Ivan Kanakarakis <ivan.kanak@gmail.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/tests/test_xsw.py b/tests/test_xsw.py
index cb756f76..0e92a5bd 100644
--- a/tests/test_xsw.py
+++ b/tests/test_xsw.py
@@ -18,6 +18,8 @@ SIGNED_XSW_ASSERTION_WRAPPER = full_path("xsw/signed-xsw-assertion-wrapper.xml")
 SIGNED_XSW_ASSERTION_EXTENSIONS = full_path("xsw/signed-xsw-assertion-extensions.xml")
 SIGNED_XSW_ASSERTION_ASSERTION = full_path("xsw/signed-xsw-assertion-assertion.xml")
 
+SIGNED_ASSERTION_FIRST_SIG = full_path("xsw/signed-xsw-assertion-in-assertion-first-sig.xml")
+SIGNED_REPONSE_FIRST_SIG = full_path("xsw/signed-xsw-response-in-response-first-sig.xml")
 
 
 class TestXSW:
@@ -87,3 +89,42 @@ class TestXSW:
 
         assert self.ar.ava is None
         assert self.ar.name_id is None
+
+
+class TestInvalidDepthFirstSig:
+    def setup_class(self):
+        self.conf = config_factory("sp", dotname("server_conf"))
+        self.ar = authn_response(self.conf, return_addrs="https://example.org/acs/post")
+
+    @patch('saml2.response.validate_on_or_after', return_value=True)
+    def test_signed_assertion_first_sig_should_fail(self, mock_validate_on_or_after):
+        self.ar.issue_instant_ok = Mock(return_value=True)
+
+        with open(SIGNED_ASSERTION_FIRST_SIG) as fp:
+            xml_response = fp.read()
+
+        self.ar.outstanding_queries = {"id-abc": "http://localhost:8088/sso"}
+        self.ar.timeslack = 10000
+        self.ar.loads(xml_response, decode=False)
+
+        assert self.ar.came_from == 'http://localhost:8088/sso'
+        assert self.ar.session_id() == "id-abc"
+        assert self.ar.issuer() == 'urn:mace:example.com:saml:roland:idp'
+
+        with raises(SignatureError):
+            self.ar.verify()
+
+        assert self.ar.ava is None
+        assert self.ar.name_id is None
+
+    @patch('saml2.response.validate_on_or_after', return_value=True)
+    def test_signed_response_first_sig_should_fail(self, mock_validate_on_or_after):
+        self.ar.issue_instant_ok = Mock(return_value=True)
+
+        with open(SIGNED_REPONSE_FIRST_SIG) as fp:
+            xml_response = fp.read()
+
+        self.ar.outstanding_queries = {"id-abc": "http://localhost:8088/sso"}
+        self.ar.timeslack = 10000
+        with raises(SignatureError):
+            self.ar.loads(xml_response, decode=False)