diff --git a/.github/workflows/deploy.yaml b/.github/workflows/deploy.yaml
index dca9c15..9da1991 100644
--- a/.github/workflows/deploy.yaml
+++ b/.github/workflows/deploy.yaml
@@ -56,7 +56,7 @@ jobs:
     uses: Sea-Haven-Industries/.github/.github/workflows/cd-cdk.yaml@7ac3528750b346f181347bb09f6af927a1c0aa14 # v1.0.6
     with:
       node-version: "24"
-      stacks: "prod-baseline dynamodb-cmk-prod alarm-topic-prod deploy-substrate-prod terraform-substrate-prod"
+      stacks: "prod-baseline dynamodb-cmk-prod alarm-topic-prod deploy-substrate-prod terraform-substrate-prod app-web-acl-prod"
       stack-name: "seahaven-prod-baseline"
     secrets:
       deploy-role-arn: ${{ secrets.AWS_DEPLOY_ROLE_ARN_PROD }}
diff --git a/README.md b/README.md
index adb9d50..57c4fdc 100644
--- a/README.md
+++ b/README.md
@@ -69,6 +69,7 @@ the TypeScript source — no separate compile step needed for `cdk synth` /
 | `deploy-substrate-dev` | `seahaven-deploy-substrate` | 710827005802 | us-east-1 | `lib/deploy-substrate-stack.ts` |
 | `dynamodb-cmk-prod` | `seahaven-dynamodb-cmk` | 011934824531 | us-east-1 | `lib/dynamodb-cmk-stack.ts` |
 | `alarm-topic-prod` | `seahaven-alarm-topic` | 011934824531 | us-east-1 | `lib/alarm-topic-stack.ts` |
+| `app-web-acl-prod` | `seahaven-app-web-acl` | 011934824531 | us-east-1 | `lib/app-web-acl-stack.ts` |
 
 Member-account stacks deploy with per-account credentials — the CD workflow
 runs one job per account, each assuming that account's OIDC deploy role. Local
diff --git a/bin/app.ts b/bin/app.ts
index af49987..b42a902 100644
--- a/bin/app.ts
+++ b/bin/app.ts
@@ -9,6 +9,7 @@ import { RegionalBaselineStack } from "../lib/regional-baseline-stack";
 import { DeploySubstrateStack } from "../lib/deploy-substrate-stack";
 import { TerraformSubstrateStack } from "../lib/terraform-substrate-stack";
 import { DynamoDbCmkStack } from "../lib/dynamodb-cmk-stack";
+import { AppWebAclStack } from "../lib/app-web-acl-stack";
 import { MemberBaselineStack } from "../lib/member-baseline-stack";
 import { OrgGovernanceStack } from "../lib/org-governance-stack";
 
@@ -207,6 +208,15 @@ const terraformSubstrateProd = new TerraformSubstrateStack(
 );
 terraformSubstrateProd.addStackDependency(deploySubstrateProd);
 
+// Shared CloudFront WAF for seahaven-prod (PLAT-92). Same AppWebAcl construct
+// as mgmt account-baseline; thin stack so prod does not inherit the full
+// mgmt baseline. Publishes /seahaven/waf/app-web-acl-arn for in-account
+// CloudFront associations (same-account only).
+new AppWebAclStack(app, "app-web-acl-prod", {
+  stackName: "seahaven-app-web-acl",
+  env: { account: PROD_ACCOUNT, region: "us-east-1" },
+});
+
 const terraformSubstrateDev = new TerraformSubstrateStack(
   app,
   "terraform-substrate-dev",
diff --git a/lib/app-web-acl-stack.ts b/lib/app-web-acl-stack.ts
new file mode 100644
index 0000000..30d7ae2
--- /dev/null
+++ b/lib/app-web-acl-stack.ts
@@ -0,0 +1,25 @@
+import * as cdk from "aws-cdk-lib";
+import { Construct } from "constructs";
+import { AppWebAcl } from "./web-acl";
+
+/**
+ * Thin per-account stack that owns the shared CloudFront WAFv2 WebACL (M-17)
+ * and publishes its ARN to SSM `/seahaven/waf/app-web-acl-arn`.
+ *
+ * Mgmt already has this ACL inside `AccountBaselineStack`. Workload accounts
+ * (starting with seahaven-prod / PLAT-92) get a dedicated stack so we do not
+ * pull the full mgmt baseline (trail, budgets, flow logs, …) into prod just
+ * to share a CloudFront WAF. App stacks associate by reading the SSM param
+ * in-account — WAFv2 CloudFront associations are same-account only.
+ */
+export class AppWebAclStack extends cdk.Stack {
+  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
+    super(scope, id, props);
+
+    new AppWebAcl(this, "AppWebAcl");
+
+    cdk.Tags.of(this).add("Project", "account-baseline");
+    cdk.Tags.of(this).add("Owner", "adam@seahavenind.com");
+    cdk.Tags.of(this).add("ManagedBy", "cdk");
+  }
+}
diff --git a/lib/terraform-substrate/terraform-substrate.template.yaml b/lib/terraform-substrate/terraform-substrate.template.yaml
index dbe482d..ab93017 100644
--- a/lib/terraform-substrate/terraform-substrate.template.yaml
+++ b/lib/terraform-substrate/terraform-substrate.template.yaml
@@ -1482,6 +1482,19 @@ Resources:
                   - acm:ListTagsForCertificate
                   - acm:GetCertificate
                 Resource: "*"
+              - Sid: RefreshAppWebAclSsm
+                Effect: Allow
+                Action:
+                  - ssm:GetParameter
+                  - ssm:GetParameters
+                Resource:
+                  - !Sub "arn:aws:ssm:us-east-1:${AWS::AccountId}:parameter/seahaven/waf/app-web-acl-arn"
+              - Sid: RefreshWafWebAcl
+                Effect: Allow
+                Action:
+                  - wafv2:GetWebACL
+                  - wafv2:ListWebACLs
+                Resource: "*"
 
   HcptfSeahavenSiteApplyRole:
     Type: AWS::IAM::Role
@@ -1554,3 +1567,21 @@ Resources:
                 Condition:
                   StringEquals:
                     "aws:ResourceTag/Project": seahaven-site
+              # CloudFront web_acl_id is set via UpdateDistribution (cloudfront:*
+              # above). Read the shared ACL ARN from SSM (PLAT-92) and allow
+              # WAFv2 describe so plans/applies can validate the association.
+              - Sid: ReadAppWebAclSsm
+                Effect: Allow
+                Action:
+                  - ssm:GetParameter
+                  - ssm:GetParameters
+                Resource:
+                  - !Sub "arn:aws:ssm:us-east-1:${AWS::AccountId}:parameter/seahaven/waf/app-web-acl-arn"
+              - Sid: ReadWafWebAcl
+                Effect: Allow
+                Action:
+                  - wafv2:GetWebACL
+                  - wafv2:GetWebACLForResource
+                  - wafv2:ListWebACLs
+                  - wafv2:ListResourcesForWebACL
+                Resource: "*"