diff --git a/cdk/lib/constructs/cf-lambda-furl-service/service.ts b/cdk/lib/constructs/cf-lambda-furl-service/service.ts
index b1cbb6a..39fc7ae 100644
--- a/cdk/lib/constructs/cf-lambda-furl-service/service.ts
+++ b/cdk/lib/constructs/cf-lambda-furl-service/service.ts
@@ -1,6 +1,6 @@
 import { Construct } from 'constructs';
-import { Duration } from 'aws-cdk-lib';
-import { FunctionUrlAuthType, Function, InvokeMode } from 'aws-cdk-lib/aws-lambda';
+import { Aws, Duration } from 'aws-cdk-lib';
+import { FunctionUrlAuthType, Function, InvokeMode, CfnPermission } from 'aws-cdk-lib/aws-lambda';
 import {
   AllowedMethods,
   CacheCookieBehavior,
@@ -120,6 +120,18 @@ export class CloudFrontLambdaFunctionUrlService extends Construct {
       minimumProtocolVersion: SecurityPolicyProtocol.TLS_V1_2_2021,
     });
 
+    // Starting October 2025, new function URLs require both lambda:InvokeFunctionUrl
+    // and lambda:InvokeFunction permissions for CloudFront OAC.
+    // CDK's FunctionUrlOrigin.withOriginAccessControl only adds lambda:InvokeFunctionUrl,
+    // so we explicitly add lambda:InvokeFunction here.
+    // See: https://docs.aws.amazon.com/lambda/latest/dg/urls-auth.html
+    new CfnPermission(this, 'InvokeFunctionPermission', {
+      action: 'lambda:InvokeFunction',
+      functionName: handler.functionArn,
+      principal: 'cloudfront.amazonaws.com',
+      sourceArn: `arn:${Aws.PARTITION}:cloudfront::${Aws.ACCOUNT_ID}:distribution/${distribution.distributionId}`,
+    });
+
     if (hostedZone) {
       new ARecord(this, 'Record', {
         zone: hostedZone,
diff --git a/cdk/lib/main-stack.ts b/cdk/lib/main-stack.ts
index ac5db01..ef42305 100644
--- a/cdk/lib/main-stack.ts
+++ b/cdk/lib/main-stack.ts
@@ -4,7 +4,7 @@ import { Construct } from 'constructs';
 import { AsyncJob } from './constructs/async-job';
 import { Auth } from './constructs/auth/';
 import { Database } from './constructs/database';
-import { InstanceClass, InstanceSize, InstanceType, NatProvider, Vpc } from 'aws-cdk-lib/aws-ec2';
+import { InstanceClass, InstanceSize, InstanceType, NatProvider, UserData, Vpc } from 'aws-cdk-lib/aws-ec2';
 import { HostedZone } from 'aws-cdk-lib/aws-route53';
 import { ICertificate } from 'aws-cdk-lib/aws-certificatemanager';
 import { Webapp } from './constructs/webapp';
@@ -56,12 +56,31 @@ export class MainStack extends Stack {
       autoDeleteObjects: true,
     });
 
+    // Custom user data for NAT instance to support Amazon Linux 2023.
+    // CDK's default user data uses `route` command which requires net-tools package,
+    // but AL2023 doesn't have net-tools pre-installed. We use `ip route` instead.
+    // Retry yum install to handle RPM lock conflicts during boot.
+    const natUserData = UserData.forLinux();
+    natUserData.addCommands(
+      // Retry yum install up to 5 times with 10 second intervals
+      'for i in {1..5}; do yum install iptables-services -y && break || sleep 10; done',
+      'systemctl enable iptables',
+      'systemctl start iptables',
+      'echo "net.ipv4.ip_forward=1" > /etc/sysctl.d/custom-ip-forwarding.conf',
+      'sysctl -p /etc/sysctl.d/custom-ip-forwarding.conf',
+      "IFACE=$(ip route show default | awk '{print $5}')",
+      '/sbin/iptables -t nat -A POSTROUTING -o $IFACE -j MASQUERADE',
+      '/sbin/iptables -F FORWARD',
+      'service iptables save',
+    );
+
     const vpc = new Vpc(this, `Vpc`, {
       ...(useNatInstance
         ? {
             natGatewayProvider: NatProvider.instanceV2({
               instanceType: InstanceType.of(InstanceClass.T4G, InstanceSize.NANO),
               associatePublicIpAddress: true,
+              userData: natUserData,
             }),
             natGateways: 1,
           }
diff --git a/cdk/test/__snapshots__/serverless-fullstack-webapp-starter-kit-without-domain.test.ts.snap b/cdk/test/__snapshots__/serverless-fullstack-webapp-starter-kit-without-domain.test.ts.snap
index 4c6b442..7b58331 100644
--- a/cdk/test/__snapshots__/serverless-fullstack-webapp-starter-kit-without-domain.test.ts.snap
+++ b/cdk/test/__snapshots__/serverless-fullstack-webapp-starter-kit-without-domain.test.ts.snap
@@ -2712,14 +2712,15 @@ exports.handler = async function (event, context) {
         ],
         "UserData": {
           "Fn::Base64": "#!/bin/bash
-yum install iptables-services -y
+for i in {1..5}; do yum install iptables-services -y && break || sleep 10; done
 systemctl enable iptables
 systemctl start iptables
 echo "net.ipv4.ip_forward=1" > /etc/sysctl.d/custom-ip-forwarding.conf
-sudo sysctl -p /etc/sysctl.d/custom-ip-forwarding.conf
-sudo /sbin/iptables -t nat -A POSTROUTING -o $(route | awk '/^default/{print $NF}') -j MASQUERADE
-sudo /sbin/iptables -F FORWARD
-sudo service iptables save",
+sysctl -p /etc/sysctl.d/custom-ip-forwarding.conf
+IFACE=$(ip route show default | awk '{print $5}')
+/sbin/iptables -t nat -A POSTROUTING -o $IFACE -j MASQUERADE
+/sbin/iptables -F FORWARD
+service iptables save",
         },
       },
       "Type": "AWS::EC2::Instance",
@@ -3684,6 +3685,38 @@ sudo service iptables save",
       },
       "Type": "AWS::IAM::Policy",
     },
+    "WebappInvokeFunctionPermission8F3F2610": {
+      "Properties": {
+        "Action": "lambda:InvokeFunction",
+        "FunctionName": {
+          "Fn::GetAtt": [
+            "WebappHandler8DD158A3",
+            "Arn",
+          ],
+        },
+        "Principal": "cloudfront.amazonaws.com",
+        "SourceArn": {
+          "Fn::Join": [
+            "",
+            [
+              "arn:",
+              {
+                "Ref": "AWS::Partition",
+              },
+              ":cloudfront::",
+              {
+                "Ref": "AWS::AccountId",
+              },
+              ":distribution/",
+              {
+                "Ref": "Webapp107041BD",
+              },
+            ],
+          ],
+        },
+      },
+      "Type": "AWS::Lambda::Permission",
+    },
     "WebappMigrationRunnerAC67C012": {
       "DependsOn": [
         "VpcPrivateSubnet1DefaultRouteBE02A9ED",
diff --git a/cdk/test/__snapshots__/serverless-fullstack-webapp-starter-kit.test.ts.snap b/cdk/test/__snapshots__/serverless-fullstack-webapp-starter-kit.test.ts.snap
index 4cb5db9..d02589b 100644
--- a/cdk/test/__snapshots__/serverless-fullstack-webapp-starter-kit.test.ts.snap
+++ b/cdk/test/__snapshots__/serverless-fullstack-webapp-starter-kit.test.ts.snap
@@ -2544,14 +2544,15 @@ exports[`Snapshot test 2`] = `
         ],
         "UserData": {
           "Fn::Base64": "#!/bin/bash
-yum install iptables-services -y
+for i in {1..5}; do yum install iptables-services -y && break || sleep 10; done
 systemctl enable iptables
 systemctl start iptables
 echo "net.ipv4.ip_forward=1" > /etc/sysctl.d/custom-ip-forwarding.conf
-sudo sysctl -p /etc/sysctl.d/custom-ip-forwarding.conf
-sudo /sbin/iptables -t nat -A POSTROUTING -o $(route | awk '/^default/{print $NF}') -j MASQUERADE
-sudo /sbin/iptables -F FORWARD
-sudo service iptables save",
+sysctl -p /etc/sysctl.d/custom-ip-forwarding.conf
+IFACE=$(ip route show default | awk '{print $5}')
+/sbin/iptables -t nat -A POSTROUTING -o $IFACE -j MASQUERADE
+/sbin/iptables -F FORWARD
+service iptables save",
         },
       },
       "Type": "AWS::EC2::Instance",
@@ -3490,6 +3491,38 @@ sudo service iptables save",
       },
       "Type": "AWS::IAM::Policy",
     },
+    "WebappInvokeFunctionPermission8F3F2610": {
+      "Properties": {
+        "Action": "lambda:InvokeFunction",
+        "FunctionName": {
+          "Fn::GetAtt": [
+            "WebappHandler8DD158A3",
+            "Arn",
+          ],
+        },
+        "Principal": "cloudfront.amazonaws.com",
+        "SourceArn": {
+          "Fn::Join": [
+            "",
+            [
+              "arn:",
+              {
+                "Ref": "AWS::Partition",
+              },
+              ":cloudfront::",
+              {
+                "Ref": "AWS::AccountId",
+              },
+              ":distribution/",
+              {
+                "Ref": "Webapp107041BD",
+              },
+            ],
+          ],
+        },
+      },
+      "Type": "AWS::Lambda::Permission",
+    },
     "WebappMigrationRunnerAC67C012": {
       "DependsOn": [
         "VpcPrivateSubnet1DefaultRouteBE02A9ED",