Broken Access Control in Gin with Dynamodb

Broken Access Control occurs when an API fails to enforce proper authorization between subjects and resources. In a Gin-based service that uses DynamoDB as the data store, the risk is the intersection of HTTP routing and per-request data access decisions. If authorization checks are performed only at the HTTP handler level and not re-validated against the data model, attackers can manipulate identifiers (IDs) in URLs or headers to access other users' records stored in DynamoDB.

Consider a Gin endpoint like /users/:userID/profile. A typical vulnerability pattern is to look up the profile in DynamoDB using :userID directly without confirming that the authenticated subject is allowed to view that specific userID. Because DynamoDB is a NoSQL key-value store, if the primary key (e.g., userID) is attacker-controlled and the service does not enforce a binding between the authenticated session and the requested key, horizontal privilege escalation occurs. This maps to BOLA/IDOR in the 12 security checks and commonly maps to OWASP API Top 10 A1: Broken Object Level Authorization.

DynamoDB-specific factors amplify the risk. In relational databases, row-level security or views may implicitly limit exposure; with DynamoDB, access patterns are explicit in application code. If the service uses a shared table for multiple tenants and relies only on client-supplied keys, an attacker can iterate or guess valid keys (e.g., UUIDs or incremental integers) to enumerate data. This is a BFLA/Privilege Escalation concern when one user can change IDs to access another’s data. Additionally, if the service uses IAM credentials associated with broad read/write permissions for DynamoDB, the blast radius is larger; compromised application logic can lead to wider data exposure.

An example vulnerable Gin handler:

// GET /users/:userID/profile
func GetUserProfile(c *gin.Context) {
    userID := c.Param("userID")
    // Vulnerable: no check that currentUser matches userID
    item, err := dynamo.GetItem(&dynamodb.GetItemInput{
        TableName: aws.String("Users"),
        Key: map[string]types.AttributeValue{
            "userID": &types.AttributeValueMemberS{Value: userID},
        },
    })
    if err != nil {
        c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
        return
    }
    c.JSON(http.StatusOK, item.Item)
}

In this pattern, an authenticated user can change userID to any value and retrieve another profile if the backend does not enforce that the requesting subject’s identity matches the requested userID. The scan’s Authorization and BOLA/IDOR checks would flag this, and findings would include guidance to bind the session subject to the data key and to apply per-request authorization.

Remediation centers on ensuring that every DynamoDB read or write is gated by a server-side authorization check that binds the authenticated subject to the data key. Do not trust client-supplied identifiers alone; derive keys from the authenticated identity or enforce ownership checks after retrieval.

1) Bind the authenticated subject to the DynamoDB key. Instead of using the client-supplied ID as the key, derive the key from the authenticated session and validate that the requested ID matches.

// Secure version: bind session userID to the request
func GetUserProfileSecure(c *gin.Context) {
    // Assume authMiddleware sets currentUser from session/JWT
    currentUser := c.MustGet("user").(models.User)
    requestedID := c.Param("userID")

    if currentUser.ID != requestedID {
        c.JSON(http.StatusForbidden, gin.H{"error": "access denied"})
        return
    }

    item, err := dynamo.GetItem(&dynamodb.GetItemInput{
        TableName: aws.String("Users"),
        Key: map[string]types.AttributeValue{
            "userID": &types.AttributeValueMemberS{Value: requestedID},
        },
    })
    if err != nil {
        c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
        return
    }
    if item.Item == nil {
        c.JSON(http.StatusNotFound, gin.H{"error": "not found"})
        return
    }
    c.JSON(http.StatusOK, item.Item)
}

2) Use a composite key design to isolate tenant or user data. Store a partition key that includes the subject identifier (e.g., USER#<userID>) and require that queries include this full key. This prevents enumeration across users even if IDs are guessable.

// Using a composite key: PK = USER#userID
func GetUserOrders(c *gin.Context) {
    currentUser := c.MustGet("user").(models.User)
    pk := "USER#" + currentUser.ID

    // Query using the composite partition key; sort key could be timestamp or orderID
    out, err := dynamo.Query(&dynamodb.QueryInput{
        TableName: aws.String("Orders"),
        KeyConditionExpression: aws.String("PK = :pk"),
        ExpressionAttributeValues: map[string]types.AttributeValue{
            ":pk": &types.AttributeValueMemberS{Value: pk},
        },
    })
    if err != nil {
        c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
        return
    }
    c.JSON(http.StatusOK, out.Items)
}

3) Enforce least privilege IAM roles for DynamoDB. Ensure the service role used by Gin does not have broad dynamodb:GetItem or dynamodb:Scan permissions scoped to the entire table; scope to keys that the application owns (e.g., prefix-based policies). While this does not replace application-level checks, it limits impact if logic is misused.

4) Validate and canonicalize IDs to avoid injection-style mistakes. Ensure userID is of expected format (e.g., UUID regex) before using it in a DynamoDB key to avoid accidental key mismatch or injection of special characters.

// Basic format validation before using as key
var uuidRegex = regexp.MustCompile(`^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$`)
if !uuidRegex.MatchString(userID) {
    c.JSON(http.StatusBadRequest, gin.H{"error": "invalid user ID format"})
    return
}

These steps ensure that authorization is enforced server-side, that data keys are bound to the authenticated subject, and that DynamoDB access patterns do not expose BOLA/IDOR or privilege escalation paths. The scan’s Authorization and BOLA/IDOR checks will verify these controls, and findings will include remediation guidance tied to the specific Gin and DynamoDB context.