Bola Idor in Chi with Dynamodb

Broken Object Level Authorization (BOLA) occurs when an API exposes references to objects without verifying that the requesting identity has permission to access them. In Chi, a lightweight Go web framework, developers often integrate with DynamoDB to store and retrieve application data. When authorization checks are omitted or incorrectly applied around DynamoDB operations, BOLA becomes likely.

Consider a typical endpoint in Chi that fetches a user profile by ID. If the route parameter (e.g., /profiles/{id}) is used directly as a DynamoDB key without confirming the profile belongs to the authenticated subject, an attacker can enumerate or manipulate IDs to access other users’ data. DynamoDB’s key-based model means items are uniquely identified by partition (and sort) keys; if those keys are predictable or weakly mapped to access controls, the risk increases. For example, using a simple integer user ID as the partition key without scoping queries to the authenticated user enables horizontal privilege escalation across accounts.

In Chi, middleware can extract claims (such as a subject identifier) from JWTs, but if that claim is not enforced at the DynamoDB request level, the vulnerability persists. An attacker making unauthenticated or low-privilege requests can send crafted requests with arbitrary IDs, and the backend will perform DynamoDB GetItem or Query operations without validating ownership. Because DynamoDB does not enforce row-level permissions natively, the application must enforce this in code. Without explicit checks, sensitive records are exposed, potentially including PII, payment information, or internal metadata, aligning with OWASP API Top 10 and categories such as Broken Object Level Authorization.

Real-world patterns include using DynamoDB with composite keys where the partition key incorporates the user tenant or subject, but the application fails to include that scope in queries. For instance, a user_id prefix might be intended to isolate data, yet the Chi handler might query using only the provided ID, inadvertently crossing tenant boundaries. This misconfiguration can also amplify risks in systems with fine-grained permissions, where an over-privileged service role or misapplied IAM policy allows broader reads than intended.

Additionally, indirect object references through secondary indexes can expose BOLA in Chi/DynamoDB setups. If a global secondary index (GSI) is used for querying without proper access controls, an attacker may leverage the index to retrieve items they should not see. Logging and error messages in Chi can inadvertently reveal item existence or structure, aiding enumeration. The combination of Chi’s flexible routing, DynamoDB’s key-based access model, and missing authorization logic creates a scenario where object-level authorization is bypassed, leading to unauthorized data exposure.

To remediate BOLA in Chi with DynamoDB, enforce ownership and scope checks on every data access operation. Always include the authenticated subject (and tenant, if applicable) as part of the key condition or filter, and avoid using user-supplied identifiers directly as keys without validation.

Example: Safe GetItem with subject scoping

import (
    "context"
    "github.com/go-chi/chi/v5"
    "github.com/aws/aws-sdk-go-v2/service/dynamodb"
    "github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
)

func getProfileHandler(db *dynamodb.Client) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        // Assume subject is extracted from JWT claims by middleware
        subject := r.Context().Value("subject").(string)
        profileID := chi.URLParam(r, "id")

        // Enforce that the requested profile belongs to the subject
        // Use a composite key: subject#profileID as partition key
        key := map[string]types.AttributeValue{
            "pk": &types.AttributeValueMemberS{Value: subject + "#" + profileID},
        }
        out, err := db.GetItem(r.Context(), &dynamodb.GetItemInput{
            TableName: aws.String("Profiles"),
            Key:       key,
        })
        if err != nil || out.Item == nil {
            http.Error(w, "not found", 404)
            return
        }
        // Marshal out.Item to JSON response
        // ...
    }
}

Example: Query with explicit ownership filter

func listUserItemsHandler(db *dynamodb.Client) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        subject := r.Context().Value("subject").(string)
        // Query only items scoped to the subject
        keyCondition := "pk = :pkval"
        expressionAttrValues := map[string]types.AttributeValue{
            ":pkval": &types.AttributeValueMemberS{Value: subject},
        }
        out, err := db.Query(r.Context(), &dynamodb.QueryInput{
            TableName:                 aws.String("UserData"),
            KeyConditionExpression:    aws.String(keyCondition),
            ExpressionAttributeValues: expressionAttrValues,
        })
        if err != nil {
            http.Error(w, "server error", 500)
            return
        }
        // Return out.Items
    }
}

Example: Validate tenant scope with DynamoDB condition expressions

func updateItemHandler(db *dynamodb.Client) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        subject := r.Context().Value("subject").(string)
        tenantID := r.Context().Value("tenant").(string)
        itemID := chi.URLParam(r, "itemid")

        // Ensure item belongs to tenant and subject
        condition := "attribute_exists(pk) AND tenant_id = :tid AND owner = :sub"
        exprAttrVals := map[string]types.AttributeValue{
            ":tid": &types.AttributeValueMemberS{Value: tenantID},
            ":sub": &types.AttributeValueMemberS{Value: subject},
        }
        _, err := db.UpdateItem(r.Context(), &dynamodb.UpdateItemInput{
            TableName:                 aws.String("Items"),
            Key:                       map[string]types.AttributeValue{"pk": &types.AttributeValueMemberS{Value: itemID}},
            UpdateExpression:          aws.String("set #st = :val"),
            ConditionExpression:       aws.String(condition),
            ExpressionAttributeNames:  map[string]string{"#st": "status"},
            ExpressionAttributeValues: exprAttrVals,
        })
        if err != nil {
            http.Error(w, "forbidden or not found", 403)
            return
        }
    }
}

General practices

• Always scope DynamoDB queries by authenticated subject and tenant.
• Use composite keys that embed the subject identifier rather than relying on sequential IDs.
• Validate and sanitize all user input before using it in key expressions or index queries.
• Leverage condition expressions to enforce ownership at the database level.
• Audit IAM policies to ensure least privilege; avoid broad dynamodb:GetItem permissions without resource-level constraints.