Check timestamp of signed EC2 token request

EC2 token requests contain a signature that signs the entire request,
including the access timestamp. While the signature is checked, the
timestamp is not, and so these signed requests remain valid
indefinitely, leaving the token API vulnerable to replay attacks. This
change introduces a configurable TTL for signed token requests and
ensures that the timestamp is actually validated against it.

The check will work for either an AWS Signature v1/v2 'Timestamp'
parameter[1] or the AWS Signature v4 'X-Aws-Date' header or
parameter[2].

Although this technically adds a new feature and the default value of
the feature changes behavior, this change is required to protect
credential holders and therefore must be backported to all supported
branches.

[1] https://docs.aws.amazon.com/general/latest/gr/signature-version-2.html
[2] https://docs.aws.amazon.com/general/latest/gr/sigv4-date-handling.html

Change-Id: Idb10267338b4204b435df233c636046a1ce5711f
Closes-bug: #1872737

keystone/api/_shared/EC2_S3_Resource.py

@@ -12,15 +12,20 @@
 
 # Common base resource for EC2 and S3 Authentication
 
+import datetime
+
 from oslo_serialization import jsonutils
+from oslo_utils import timeutils
 from werkzeug import exceptions
 
 from keystone.common import provider_api
 from keystone.common import utils
+import keystone.conf
 from keystone import exception as ks_exceptions
 from keystone.i18n import _
 from keystone.server import flask as ks_flask
 
+CONF = keystone.conf.CONF
 PROVIDERS = provider_api.ProviderAPIs
 CRED_TYPE_EC2 = 'ec2'
 
@@ -36,6 +41,31 @@ class ResourceBase(ks_flask.ResourceBase):
         # the ABC module.
         raise NotImplementedError()
 
+    @staticmethod
+    def _check_timestamp(credentials):
+        timestamp = (
+            # AWS Signature v1/v2
+            credentials.get('params', {}).get('Timestamp') or
+            # AWS Signature v4
+            credentials.get('headers', {}).get('X-Amz-Date') or
+            credentials.get('params', {}).get('X-Amz-Date')
+        )
+        if not timestamp:
+            # If the signed payload doesn't include a timestamp then the signer
+            # must have intentionally left it off
+            return
+        try:
+            timestamp = timeutils.parse_isotime(timestamp)
+            timestamp = timeutils.normalize_time(timestamp)
+        except Exception as e:
+            raise ks_exceptions.Unauthorized(
+                _('Credential timestamp is invalid: %s') % e)
+        auth_ttl = datetime.timedelta(minutes=CONF.credential.auth_ttl)
+        current_time = timeutils.normalize_time(timeutils.utcnow())
+        if current_time > timestamp + auth_ttl:
+            raise ks_exceptions.Unauthorized(
+                _('Credential is expired'))
+
     def handle_authenticate(self):
         # TODO(morgan): convert this dirty check to JSON Schema validation
         # this mirrors the previous behavior of the webob system where an
@@ -101,6 +131,7 @@ class ResourceBase(ks_flask.ResourceBase):
         except AssertionError as e:
             raise ks_exceptions.Unauthorized from e
 
+        self._check_timestamp(credentials)
         roles = PROVIDERS.assignment_api.get_roles_for_user_and_project(
             user_ref['id'], project_ref['id'])
 

keystone/conf/credential.py

@@ -61,6 +61,14 @@ Time to cache credential data in seconds. This has no effect unless global
 caching is enabled.
 """))
 
+auth_ttl = cfg.IntOpt(
+    'auth_ttl',
+    default=15,
+    help=utils.fmt("""
+The length of time in minutes for which a signed EC2 or S3 token request is
+valid from the timestamp contained in the token request.
+"""))
+
 
 GROUP_NAME = __name__.split('.')[-1]
 ALL_OPTS = [
@@ -68,7 +76,8 @@ ALL_OPTS = [
     provider,
     key_repository,
     caching,
-    cache_time
+    cache_time,
+    auth_ttl
 ]
 
 

keystone/tests/unit/test_contrib_ec2_core.py

@@ -12,10 +12,15 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import datetime
+import hashlib
+
 import http.client
 from keystoneclient.contrib.ec2 import utils as ec2_utils
+from oslo_utils import timeutils
 
 from keystone.common import provider_api
+from keystone.common import utils
 from keystone.tests import unit
 from keystone.tests.unit import test_v3
 
@@ -34,6 +39,7 @@ class EC2ContribCoreV3(test_v3.RestfulTestCase):
 
     def test_valid_authentication_response_with_proper_secret(self):
         signer = ec2_utils.Ec2Signer(self.cred_blob['secret'])
+        timestamp = utils.isotime(timeutils.utcnow())
         credentials = {
             'access': self.cred_blob['access'],
             'secret': self.cred_blob['secret'],
@@ -43,7 +49,7 @@ class EC2ContribCoreV3(test_v3.RestfulTestCase):
             'params': {
                 'SignatureVersion': '2',
                 'Action': 'Test',
-                'Timestamp': '2007-01-31T23:59:59Z'
+                'Timestamp': timestamp
             },
         }
         credentials['signature'] = signer.generate(credentials)
@@ -53,6 +59,48 @@ class EC2ContribCoreV3(test_v3.RestfulTestCase):
             expected_status=http.client.OK)
         self.assertValidProjectScopedTokenResponse(resp, self.user)
 
+    def test_valid_authentication_response_with_signature_v4(self):
+        signer = ec2_utils.Ec2Signer(self.cred_blob['secret'])
+        timestamp = utils.isotime(timeutils.utcnow())
+        hashed_payload = (
+            'GET\n'
+            '/\n'
+            'Action=Test\n'
+            'host:localhost\n'
+            'x-amz-date:' + timestamp + '\n'
+            '\n'
+            'host;x-amz-date\n'
+            'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855'
+        )
+        body_hash = hashlib.sha256(hashed_payload.encode()).hexdigest()
+        amz_credential = (
+            'AKIAIOSFODNN7EXAMPLE/%s/us-east-1/iam/aws4_request,' %
+            timestamp[:8])
+
+        credentials = {
+            'access': self.cred_blob['access'],
+            'secret': self.cred_blob['secret'],
+            'host': 'localhost',
+            'verb': 'GET',
+            'path': '/',
+            'params': {
+                'Action': 'Test',
+                'X-Amz-Algorithm': 'AWS4-HMAC-SHA256',
+                'X-Amz-SignedHeaders': 'host,x-amz-date,',
+                'X-Amz-Credential': amz_credential
+            },
+            'headers': {
+                'X-Amz-Date': timestamp
+            },
+            'body_hash': body_hash
+        }
+        credentials['signature'] = signer.generate(credentials)
+        resp = self.post(
+            '/ec2tokens',
+            body={'credentials': credentials},
+            expected_status=http.client.OK)
+        self.assertValidProjectScopedTokenResponse(resp, self.user)
+
     def test_authenticate_with_empty_body_returns_bad_request(self):
         self.post(
             '/ec2tokens',
@@ -72,6 +120,7 @@ class EC2ContribCoreV3(test_v3.RestfulTestCase):
 
     def test_authenticate_without_proper_secret_returns_unauthorized(self):
         signer = ec2_utils.Ec2Signer('totally not the secret')
+        timestamp = utils.isotime(timeutils.utcnow())
         credentials = {
             'access': self.cred_blob['access'],
             'secret': 'totally not the secret',
@@ -81,7 +130,7 @@ class EC2ContribCoreV3(test_v3.RestfulTestCase):
             'params': {
                 'SignatureVersion': '2',
                 'Action': 'Test',
-                'Timestamp': '2007-01-31T23:59:59Z'
+                'Timestamp': timestamp
             },
         }
         credentials['signature'] = signer.generate(credentials)
@@ -89,3 +138,75 @@ class EC2ContribCoreV3(test_v3.RestfulTestCase):
             '/ec2tokens',
             body={'credentials': credentials},
             expected_status=http.client.UNAUTHORIZED)
+
+    def test_authenticate_expired_request(self):
+        self.config_fixture.config(
+            group='credential',
+            auth_ttl=5
+        )
+        signer = ec2_utils.Ec2Signer(self.cred_blob['secret'])
+        past = timeutils.utcnow() - datetime.timedelta(minutes=10)
+        timestamp = utils.isotime(past)
+        credentials = {
+            'access': self.cred_blob['access'],
+            'secret': self.cred_blob['secret'],
+            'host': 'localhost',
+            'verb': 'GET',
+            'path': '/',
+            'params': {
+                'SignatureVersion': '2',
+                'Action': 'Test',
+                'Timestamp': timestamp
+            },
+        }
+        credentials['signature'] = signer.generate(credentials)
+        self.post(
+            '/ec2tokens',
+            body={'credentials': credentials},
+            expected_status=http.client.UNAUTHORIZED)
+
+    def test_authenticate_expired_request_v4(self):
+        self.config_fixture.config(
+            group='credential',
+            auth_ttl=5
+        )
+        signer = ec2_utils.Ec2Signer(self.cred_blob['secret'])
+        past = timeutils.utcnow() - datetime.timedelta(minutes=10)
+        timestamp = utils.isotime(past)
+        hashed_payload = (
+            'GET\n'
+            '/\n'
+            'Action=Test\n'
+            'host:localhost\n'
+            'x-amz-date:' + timestamp + '\n'
+            '\n'
+            'host;x-amz-date\n'
+            'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855'
+        )
+        body_hash = hashlib.sha256(hashed_payload.encode()).hexdigest()
+        amz_credential = (
+            'AKIAIOSFODNN7EXAMPLE/%s/us-east-1/iam/aws4_request,' %
+            timestamp[:8])
+
+        credentials = {
+            'access': self.cred_blob['access'],
+            'secret': self.cred_blob['secret'],
+            'host': 'localhost',
+            'verb': 'GET',
+            'path': '/',
+            'params': {
+                'Action': 'Test',
+                'X-Amz-Algorithm': 'AWS4-HMAC-SHA256',
+                'X-Amz-SignedHeaders': 'host,x-amz-date,',
+                'X-Amz-Credential': amz_credential
+            },
+            'headers': {
+                'X-Amz-Date': timestamp
+            },
+            'body_hash': body_hash
+        }
+        credentials['signature'] = signer.generate(credentials)
+        self.post(
+            '/ec2tokens',
+            body={'credentials': credentials},
+            expected_status=http.client.UNAUTHORIZED)

releasenotes/notes/bug-1872737-f8e1ad3b6705b766.yaml

@@ -0,0 +1,28 @@
+---
+feature:
+  - |
+    [`bug 1872737 <https://bugs.launchpad.net/keystone/+bug/1872737>`_]
+    Added a new config option ``auth_ttl`` in the ``[credential]`` config
+    section to allow configuring the period for which a signed token request
+    from AWS is valid. The default is 15 minutes in accordance with the AWS
+    Signature V4 API reference.
+upgrade:
+  - |
+    [`bug 1872737 <https://bugs.launchpad.net/keystone/+bug/1872737>`_]
+    Added a default TTL of 15 minutes for signed EC2 credential requests,
+    where previously an EC2 signed token request was valid indefinitely. This
+    change in behavior is needed to protect against replay attacks.
+security:
+  - |
+    [`bug 1872737 <https://bugs.launchpad.net/keystone/+bug/1872737>`_]
+    Fixed an incorrect EC2 token validation implementation in which the
+    timestamp of the signed request was ignored, which made EC2 and S3 token
+    requests vulnerable to replay attacks. The default TTL is 15 minutes but
+    is configurable.
+fixes:
+  - |
+    [`bug 1872737 <https://bugs.launchpad.net/keystone/+bug/1872737>`_]
+    Fixed an incorrect EC2 token validation implementation in which the
+    timestamp of the signed request was ignored, which made EC2 and S3 token
+    requests vulnerable to replay attacks. The default TTL is 15 minutes but
+    is configurable.