feat(elb): add new check elb_desync_mitigation_mode (#5500)

Co-authored-by: Sergio <sergio@prowler.com>
2026-07-24 13:01:56 +00:00 · 2024-10-22 20:08:13 +02:00
parent 8ac28fbcfd
commit f36d23c9a7
10 changed files with 351 additions and 11 deletions
@@ -0,0 +1,32 @@
+{
+  "Provider": "aws",
+  "CheckID": "elb_desync_mitigation_mode",
+  "CheckTitle": "Classic Load Balancer should be configured with defensive or strictest desync mitigation mode",
+  "CheckType": [
+    "Software and Configuration Checks/AWS Security Best Practices"
+  ],
+  "ServiceName": "elb",
+  "SubServiceName": "",
+  "ResourceIdTemplate": "arn:aws:elasticloadbalancing:{region}:{account-id}:loadbalancer/{load-balancer-name}",
+  "Severity": "medium",
+  "ResourceType": "AwsElbLoadBalancer",
+  "Description": "This control checks whether a Classic Load Balancer is configured with defensive or strictest desync mitigation mode. The control fails if the Classic Load Balancer isn't configured with defensive or strictest desync mitigation mode.",
+  "Risk": "HTTP Desync issues can lead to request smuggling, making applications vulnerable to attacks such as request queue or cache poisoning, which could result in credential hijacking or unauthorized command execution.",
+  "RelatedUrl": "https://docs.aws.amazon.com/config/latest/developerguide/clb-desync-mode-check.html",
+  "Remediation": {
+    "Code": {
+      "CLI": "aws elb modify-load-balancer-attributes --load-balancer-name <load-balancer-name> --load-balancer-attributes '{\"DesyncMitigationMode\":\"defensive\"}'",
+      "NativeIaC": "",
+      "Other": "https://docs.aws.amazon.com/securityhub/latest/userguide/elb-controls.html#elb-14",
+      "Terraform": ""
+    },
+    "Recommendation": {
+      "Text": "Configure the Classic Load Balancer with defensive or strictest desync mitigation mode to prevent security issues caused by HTTP desync.",
+      "Url": "https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/config-desync-mitigation-mode.html#update-desync-mitigation-mode"
+    }
+  },
+  "Categories": [],
+  "DependsOn": [],
+  "RelatedTo": [],
+  "Notes": ""
+}
@@ -0,0 +1,26 @@
+from prowler.lib.check.models import Check, Check_Report_AWS
+from prowler.providers.aws.services.elb.elb_client import elb_client
+
+
+class elb_desync_mitigation_mode(Check):
+    def execute(self):
+        findings = []
+        for lb_arn, lb in elb_client.loadbalancers.items():
+            report = Check_Report_AWS(self.metadata())
+            report.region = lb.region
+            report.resource_id = lb.name
+            report.resource_arn = lb_arn
+            report.resource_tags = lb.tags
+            if (
+                lb.desync_mitigation_mode == "defensive"
+                or lb.desync_mitigation_mode == "strictest"
+            ):
+                report.status = "PASS"
+                report.status_extended = f"ELB {lb.name} has desync mitigation mode set to {lb.desync_mitigation_mode}."
+            else:
+                report.status = "FAIL"
+                report.status_extended = f"ELB {lb.name} has desync mitigation mode set to {lb.desync_mitigation_mode}, not to strictest or defensive."
+
+            findings.append(report)
+
+        return findings
@@ -36,9 +36,9 @@ class ELB(AWSService):
                                Listener(
                                    protocol=listener["Listener"]["Protocol"],
                                    policies=listener["PolicyNames"],
-                                    certificate_arn=listener["Listener"][
-                                        "SSLCertificateId"
-                                    ],
+                                    certificate_arn=listener["Listener"].get(
+                                        "SSLCertificateId", ""
+                                    ),
                                )
                            )

@@ -70,6 +70,10 @@ class ELB(AWSService):
            load_balancer.connection_draining = attributes.get(
                "ConnectionDraining", {}
            ).get("Enabled", False)
+            additional_attributes = attributes.get("AdditionalAttributes", [])
+            for attribute in additional_attributes:
+                if attribute["Key"] == "elb.http.desyncmitigationmode":
+                    load_balancer.desync_mitigation_mode = attribute["Value"]

        except Exception as error:
            logger.error(
@@ -109,4 +113,5 @@ class LoadBalancer(BaseModel):
    cross_zone_load_balancing: Optional[bool]
    availability_zones: set[str]
    connection_draining: Optional[bool]
+    desync_mitigation_mode: Optional[str]
    tags: Optional[list] = []
@@ -5,11 +5,11 @@
  "CheckType": [
    "Software and Configuration Checks/Vulnerabilities/NIST 800-53 Controls (USA)"
  ],
-  "ServiceName": "elasticloadbalancing",
+  "ServiceName": "elb",
  "SubServiceName": "",
  "ResourceIdTemplate": "arn:aws:elasticloadbalancing:{region}:{account-id}:loadbalancer/{loadbalancer-name}",
  "Severity": "medium",
-  "ResourceType": "AwsElasticLoadBalancingLoadBalancer",
+  "ResourceType": "AwsElbLoadBalancer",
  "Description": "This control checks whether the Classic Load Balancer uses HTTPS/SSL certificates provided by AWS Certificate Manager (ACM). The control fails if the Classic Load Balancer does not use a certificate provided by ACM.",
  "Risk": "If Classic Load Balancers are not using ACM certificates, it increases the risk of using self-signed or expired certificates, which can impact secure communication and lead to compliance issues.",
  "RelatedUrl": "https://docs.aws.amazon.com/config/latest/developerguide/elb-acm-certificate-required.html",
@@ -17,7 +17,8 @@ class elb_ssl_listeners_use_acm_certificate(Check):
            report.status_extended = f"ELB {lb.name} HTTPS/SSL listeners are using certificates managed by ACM."
            for listener in lb.listeners:
                if (
-                    listener.protocol in secure_protocols
+                    listener.certificate_arn
+                    and listener.protocol in secure_protocols
                    and acm_client.certificates[listener.certificate_arn].type
                    != "AMAZON_ISSUED"
                ):
@@ -14,12 +14,15 @@ class elbv2_desync_mitigation_mode(Check):
                report.resource_tags = lb.tags
                report.status = "PASS"
                report.status_extended = f"ELBv2 ALB {lb.name} is configured with correct desync mitigation mode."
-                if lb.desync_mitigation_mode != "strictest":
+                if (
+                    lb.desync_mitigation_mode != "strictest"
+                    or lb.desync_mitigation_mode != "defensive"
+                ):
                    if lb.drop_invalid_header_fields == "false":
                        report.status = "FAIL"
-                        report.status_extended = f"ELBv2 ALB {lb.name} does not have desync mitigation mode set as strictest and is not dropping invalid header fields."
+                        report.status_extended = f"ELBv2 ALB {lb.name} does not have desync mitigation mode set as strictest/defensive and is not dropping invalid header fields."
                    elif lb.drop_invalid_header_fields == "true":
-                        report.status_extended = f"ELBv2 ALB {lb.name} does not have desync mitigation mode set as strictest but is dropping invalid header fields."
+                        report.status_extended = f"ELBv2 ALB {lb.name} does not have desync mitigation mode set as strictest/defensive but is dropping invalid header fields."
                findings.append(report)

        return findings
@@ -0,0 +1,272 @@
+from unittest import mock
+
+import botocore
+from boto3 import client, resource
+from moto import mock_aws
+
+from tests.providers.aws.utils import (
+    AWS_REGION_EU_WEST_1,
+    AWS_REGION_EU_WEST_1_AZA,
+    AWS_REGION_US_EAST_1,
+    set_mocked_aws_provider,
+)
+
+make_api_call = botocore.client.BaseClient._make_api_call
+
+
+def mock_make_api_call(self, operation_name, kwarg):
+    if operation_name == "DescribeLoadBalancerAttributes":
+        if kwarg["LoadBalancerName"] == "my-lb-strictest":
+            return {
+                "LoadBalancerAttributes": {
+                    "CrossZoneLoadBalancing": {"Enabled": True},
+                    "AccessLog": {
+                        "Enabled": False,
+                        "EmitInterval": 60,
+                    },
+                    "ConnectionDraining": {"Enabled": False, "Timeout": 300},
+                    "ConnectionSettings": {
+                        "IdleTimeout": 60,
+                    },
+                    "AdditionalAttributes": [
+                        {
+                            "Key": "elb.http.desyncmitigationmode",
+                            "Value": "strictest",
+                        }
+                    ],
+                }
+            }
+        if kwarg["LoadBalancerName"] == "my-lb-defensive":
+            return {
+                "LoadBalancerAttributes": {
+                    "CrossZoneLoadBalancing": {"Enabled": True},
+                    "AccessLog": {
+                        "Enabled": False,
+                        "EmitInterval": 60,
+                    },
+                    "ConnectionDraining": {"Enabled": False, "Timeout": 300},
+                    "ConnectionSettings": {
+                        "IdleTimeout": 60,
+                    },
+                    "AdditionalAttributes": [
+                        {
+                            "Key": "elb.http.desyncmitigationmode",
+                            "Value": "defensive",
+                        }
+                    ],
+                }
+            }
+        if kwarg["LoadBalancerName"] == "my-lb-monitor":
+            return {
+                "LoadBalancerAttributes": {
+                    "CrossZoneLoadBalancing": {"Enabled": True},
+                    "AccessLog": {
+                        "Enabled": False,
+                        "EmitInterval": 60,
+                    },
+                    "ConnectionDraining": {"Enabled": False, "Timeout": 300},
+                    "ConnectionSettings": {
+                        "IdleTimeout": 60,
+                    },
+                    "AdditionalAttributes": [
+                        {
+                            "Key": "elb.http.desyncmitigationmode",
+                            "Value": "monitor",
+                        }
+                    ],
+                }
+            }
+
+    return make_api_call(self, operation_name, kwarg)
+
+
+class Test_elb_desync_mitigation_mode:
+    @mock_aws
+    def test_elb_no_balancers(self):
+        from prowler.providers.aws.services.elb.elb_service import ELB
+
+        with mock.patch(
+            "prowler.providers.common.provider.Provider.get_global_provider",
+            return_value=set_mocked_aws_provider(
+                [AWS_REGION_EU_WEST_1, AWS_REGION_US_EAST_1]
+            ),
+        ), mock.patch(
+            "prowler.providers.aws.services.elb.elb_desync_mitigation_mode.elb_desync_mitigation_mode.elb_client",
+            new=ELB(
+                set_mocked_aws_provider([AWS_REGION_EU_WEST_1, AWS_REGION_US_EAST_1])
+            ),
+        ):
+            # Test Check
+            from prowler.providers.aws.services.elb.elb_desync_mitigation_mode.elb_desync_mitigation_mode import (
+                elb_desync_mitigation_mode,
+            )
+
+            check = elb_desync_mitigation_mode()
+            result = check.execute()
+
+            assert len(result) == 0
+
+    @mock_aws
+    @mock.patch("botocore.client.BaseClient._make_api_call", new=mock_make_api_call)
+    def test_elb_with_monitor_desync_mode(self):
+        elb = client("elb", region_name=AWS_REGION_EU_WEST_1)
+        ec2 = resource("ec2", region_name=AWS_REGION_EU_WEST_1)
+
+        security_group = ec2.create_security_group(
+            GroupName="sg01", Description="Test security group sg01"
+        )
+
+        elb.create_load_balancer(
+            LoadBalancerName="my-lb-monitor",
+            Listeners=[
+                {"Protocol": "tcp", "LoadBalancerPort": 80, "InstancePort": 8080},
+                {"Protocol": "http", "LoadBalancerPort": 81, "InstancePort": 9000},
+            ],
+            AvailabilityZones=[AWS_REGION_EU_WEST_1_AZA],
+            Scheme="internal",
+            SecurityGroups=[security_group.id],
+        )
+
+        from prowler.providers.aws.services.elb.elb_service import ELB
+
+        with mock.patch(
+            "prowler.providers.common.provider.Provider.get_global_provider",
+            return_value=set_mocked_aws_provider(
+                [AWS_REGION_EU_WEST_1, AWS_REGION_US_EAST_1]
+            ),
+        ), mock.patch(
+            "prowler.providers.aws.services.elb.elb_desync_mitigation_mode.elb_desync_mitigation_mode.elb_client",
+            new=ELB(
+                set_mocked_aws_provider([AWS_REGION_EU_WEST_1, AWS_REGION_US_EAST_1])
+            ),
+        ):
+            from prowler.providers.aws.services.elb.elb_desync_mitigation_mode.elb_desync_mitigation_mode import (
+                elb_desync_mitigation_mode,
+            )
+
+            check = elb_desync_mitigation_mode()
+            result = check.execute()
+
+            assert len(result) == 1
+            assert result[0].status == "FAIL"
+            assert (
+                result[0].status_extended
+                == "ELB my-lb-monitor has desync mitigation mode set to monitor, not to strictest or defensive."
+            )
+            assert result[0].resource_id == "my-lb-monitor"
+            assert (
+                result[0].resource_arn
+                == "arn:aws:elasticloadbalancing:eu-west-1:123456789012:loadbalancer/my-lb-monitor"
+            )
+            assert result[0].region == AWS_REGION_EU_WEST_1
+            assert result[0].resource_tags == []
+
+    @mock_aws
+    @mock.patch("botocore.client.BaseClient._make_api_call", new=mock_make_api_call)
+    def test_elb_with_defensive_desync_mode(self):
+        elb = client("elb", region_name=AWS_REGION_EU_WEST_1)
+        ec2 = resource("ec2", region_name=AWS_REGION_EU_WEST_1)
+
+        security_group = ec2.create_security_group(
+            GroupName="sg01", Description="Test security group sg01"
+        )
+
+        elb.create_load_balancer(
+            LoadBalancerName="my-lb-defensive",
+            Listeners=[
+                {"Protocol": "tcp", "LoadBalancerPort": 80, "InstancePort": 8080},
+                {"Protocol": "http", "LoadBalancerPort": 81, "InstancePort": 9000},
+            ],
+            AvailabilityZones=[AWS_REGION_EU_WEST_1_AZA],
+            Scheme="internal",
+            SecurityGroups=[security_group.id],
+        )
+
+        from prowler.providers.aws.services.elb.elb_service import ELB
+
+        with mock.patch(
+            "prowler.providers.common.provider.Provider.get_global_provider",
+            return_value=set_mocked_aws_provider(
+                [AWS_REGION_EU_WEST_1, AWS_REGION_US_EAST_1]
+            ),
+        ), mock.patch(
+            "prowler.providers.aws.services.elb.elb_desync_mitigation_mode.elb_desync_mitigation_mode.elb_client",
+            new=ELB(
+                set_mocked_aws_provider([AWS_REGION_EU_WEST_1, AWS_REGION_US_EAST_1])
+            ),
+        ):
+            from prowler.providers.aws.services.elb.elb_desync_mitigation_mode.elb_desync_mitigation_mode import (
+                elb_desync_mitigation_mode,
+            )
+
+            check = elb_desync_mitigation_mode()
+            result = check.execute()
+
+            assert len(result) == 1
+            assert result[0].status == "PASS"
+            assert (
+                result[0].status_extended
+                == "ELB my-lb-defensive has desync mitigation mode set to defensive."
+            )
+            assert result[0].resource_id == "my-lb-defensive"
+            assert (
+                result[0].resource_arn
+                == "arn:aws:elasticloadbalancing:eu-west-1:123456789012:loadbalancer/my-lb-defensive"
+            )
+            assert result[0].region == AWS_REGION_EU_WEST_1
+            assert result[0].resource_tags == []
+
+    @mock_aws
+    @mock.patch("botocore.client.BaseClient._make_api_call", new=mock_make_api_call)
+    def test_elb_with_strictest_desync_mode(self):
+        elb = client("elb", region_name=AWS_REGION_EU_WEST_1)
+        ec2 = resource("ec2", region_name=AWS_REGION_EU_WEST_1)
+
+        security_group = ec2.create_security_group(
+            GroupName="sg01", Description="Test security group sg01"
+        )
+
+        elb.create_load_balancer(
+            LoadBalancerName="my-lb-strictest",
+            Listeners=[
+                {"Protocol": "tcp", "LoadBalancerPort": 80, "InstancePort": 8080},
+                {"Protocol": "http", "LoadBalancerPort": 81, "InstancePort": 9000},
+            ],
+            AvailabilityZones=[AWS_REGION_EU_WEST_1_AZA],
+            Scheme="internal",
+            SecurityGroups=[security_group.id],
+        )
+
+        from prowler.providers.aws.services.elb.elb_service import ELB
+
+        with mock.patch(
+            "prowler.providers.common.provider.Provider.get_global_provider",
+            return_value=set_mocked_aws_provider(
+                [AWS_REGION_EU_WEST_1, AWS_REGION_US_EAST_1]
+            ),
+        ), mock.patch(
+            "prowler.providers.aws.services.elb.elb_desync_mitigation_mode.elb_desync_mitigation_mode.elb_client",
+            new=ELB(
+                set_mocked_aws_provider([AWS_REGION_EU_WEST_1, AWS_REGION_US_EAST_1])
+            ),
+        ):
+            from prowler.providers.aws.services.elb.elb_desync_mitigation_mode.elb_desync_mitigation_mode import (
+                elb_desync_mitigation_mode,
+            )
+
+            check = elb_desync_mitigation_mode()
+            result = check.execute()
+
+            assert len(result) == 1
+            assert result[0].status == "PASS"
+            assert (
+                result[0].status_extended
+                == "ELB my-lb-strictest has desync mitigation mode set to strictest."
+            )
+            assert result[0].resource_id == "my-lb-strictest"
+            assert (
+                result[0].resource_arn
+                == "arn:aws:elasticloadbalancing:eu-west-1:123456789012:loadbalancer/my-lb-strictest"
+            )
+            assert result[0].region == AWS_REGION_EU_WEST_1
+            assert result[0].resource_tags == []
@@ -136,6 +136,7 @@ class Test_ELB_Service:
        assert elb.loadbalancers[elb_arn].access_logs
        assert elb.loadbalancers[elb_arn].cross_zone_load_balancing
        assert elb.loadbalancers[elb_arn].connection_draining
+        assert elb.loadbalancers[elb_arn].desync_mitigation_mode is None

    # Test ELB Describe Tags
    @mock_aws
@@ -101,7 +101,7 @@ class Test_elbv2_desync_mitigation_mode:
            assert len(result) == 1
            assert result[0].status == "FAIL"
            assert search(
-                "does not have desync mitigation mode set as strictest and is not dropping invalid header fields",
+                "does not have desync mitigation mode set as strictest/defensive and is not dropping invalid header fields",
                result[0].status_extended,
            )
            assert result[0].resource_id == "my-lb"
@@ -169,7 +169,7 @@ class Test_elbv2_desync_mitigation_mode:
            assert len(result) == 1
            assert result[0].status == "PASS"
            assert search(
-                "does not have desync mitigation mode set as strictest but is dropping invalid header fields",
+                "does not have desync mitigation mode set as strictest/defensive but is dropping invalid header fields",
                result[0].status_extended,
            )
            assert result[0].resource_id == "my-lb"