Zone Transfer in Chi with Dynamodb

In a DNS context, a zone transfer is a mechanism by which secondary nameservers obtain a copy of the zone data from a primary nameserver. When DNS is misconfigured to allow zone transfers to unauthorized hosts, an attacker can retrieve the full DNS record set for a domain, including internal hostnames and IPs. In Chi, a lightweight Go HTTP router commonly used to build APIs, developers sometimes integrate with external data stores such as DynamoDB to serve or store DNS configuration and zone data. If the API endpoints in Chi that interact with DynamoDB do not enforce proper authorization, an unauthenticated or low-privileged actor may trigger logic that exports zone data, effectively enabling a zone transfer through the API layer.

The combination creates risk when:

• The Chi application exposes an administrative or debug endpoint (e.g., /debug/zone-transfer or /export/dns) that queries DynamoDB for DNS zone records without verifying the caller’s permissions.
• DynamoDB table policies or IAM roles assigned to the Chi service are over-permissive, allowing read access to sensitive zone data from untrusted network locations.
• The Chi application does not enforce rate limiting or strong authentication on DNS-export endpoints, allowing enumeration or bulk data extraction that mirrors a traditional DNS zone transfer via an API.

This scenario maps to the BOLA/IDOR and BFLA/Privilege Escalation checks run by middleBrick, where an unauthenticated attacker can retrieve sensitive data that should be restricted. For example, an endpoint like GET /api/v1/export-zone?domain=example.com that directly forwards the query to a DynamoDB table without validating the requester’s scope can disclose internal hostnames, mail servers, and infrastructure details. Such findings are surfaced by middleBrick under Data Exposure and Property Authorization, with remediation guidance to enforce strict authorization, scope-bound access, and least privilege.

To remediate zone transfer risks when using DynamoDB with Chi, focus on tightening authorization at the API layer and the data layer. In Chi, use middleware to enforce authentication and scoped authorization before allowing any export or debug functionality. Ensure that DynamoDB queries are scoped to the minimal required data and that table policies restrict who can perform dynamodb:Query or dynamodb:Scan on sensitive tables.

Example secure Chi route with scoped access checks:

// Chi route with scoped authorization and no export of full zone on unauthenticated paths
func exportZoneHandler(db *dynamodb.Client) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		// Verify request-level authentication and scope
		user, ok := r.Context().Value("user").(*User)
		if !ok {
			http.Error(w, `{"error": "unauthorized"}`, http.StatusUnauthorized)
			return
		}
		// Enforce scope: only allow export for domains the user is permitted to view
		domain := chi.URLParam(r, "domain")
		if !user.CanExportDomain(domain) {
			http.Error(w, `{"error": "forbidden"}`, http.StatusForbidden)
			return
		}

		// Query DynamoDB with a scoped key condition to avoid full table scan
		input := &dynamodb.QueryInput{
			TableName: aws.String("DNSZoneTable"),
			KeyConditionExpression: aws.String("domain = :val"),
			ExpressionAttributeValues: map[string]types.AttributeValue{
				":val": &types.AttributeValueMemberS{Value: domain},
			},
		}
		out, err := db.Query(r.Context(), input)
		if err != nil {
			http.Error(w, `{"error": "internal server error"}`, http.StatusInternalServerError)
			return
		}

		// Return only permitted records; avoid returning the entire zone file
		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(out.Items)
	}
}

On the DynamoDB side, ensure your table policies and IAM roles follow least privilege:

• Use condition keys such as dynamodb:LeadingKeys to ensure queries are scoped to the partition key owned or accessible to the requester.
• Avoid wildcard actions like dynamodb:Scan on tables that contain zone data; prefer indexed queries with explicit key conditions.
• Enable DynamoDB encryption at rest and use VPC endpoints or private links to prevent data exposure in transit, which aligns with the Encryption and Data Exposure checks performed by middleBrick.

Additionally, apply rate limiting and authentication at the Chi middleware layer to prevent enumeration that could be used for a covert zone transfer. middleBrick’s checks for Rate Limiting, Authentication, and Property Authorization will highlight missing guards on these endpoints.