Broken Access Control in Buffalo with Dynamodb

Broken Access Control occurs when authorization checks are missing or bypassed, allowing one user to act on another user's resources. In a Buffalo application using Amazon DynamoDB as the persistence layer, this risk is pronounced if the backend constructs DynamoDB requests using user-supplied identifiers without validating that the authenticated subject owns those identifiers.

Consider a typical REST pattern in Buffalo: a route like /users/:user_id/profile maps to a handler that reads a DynamoDB item using a key expression built from params["user_id"]. If the handler skips ownership validation—such as confirming the requesting user’s ID (from the session or JWT) matches the user_id in the path—an attacker can modify the URL to access or modify another user’s profile. Because DynamoDB itself does not enforce application-level ownership, the database will return the requested item as long as the key exists, effectively exposing one user’s data to another.

This becomes more severe when secondary indexes or global tables are in use. A developer might query a Global Secondary Index (GSI) using a partition key derived from organization or tenant ID. If the application fails to also enforce that the requester belongs to the same organization, the GSI can act as a horizontal escalation path, returning records across tenant boundaries. In Buffalo, this often manifests as a missing check before calling GetItem or Query, where the constructed key includes the tenant or user context supplied by the client without server-side verification.

Moreover, HTTP method misuse can compound the issue. For example, allowing a non-idempotent operation like UpdateItem on a user-specific stream without confirming ownership enables BOLA (Broken Object Level Authorization) attacks. An attacker who guesses or enumerates valid DynamoDB keys can alter or delete data. The vulnerability is not in DynamoDB but in how Buffalo builds and authorizes requests against it: missing or inconsistent authorization checks at the handler level, reliance on client-provided keys, and failure to scope queries to the requesting subject’s context.

Remediation centers on enforcing ownership and scoping every DynamoDB operation to the authenticated subject. In Buffalo, this means validating the current user’s identity against the key attributes used in DynamoDB requests before issuing any API call.

First, ensure your session or token payload includes a stable user identifier (e.g., sub or user_id). Then, in each handler, derive the DynamoDB key from both the resource identifier in the URL and the authenticated subject, and assert they align. Below is an example of a safe profile handler using the AWS SDK for Go within Buffalo:

// handlers/profile.go
package handlers

import (
    "context"
    "net/http"

    "github.com/gobuffalo/buffalo"
    "github.com/aws/aws-sdk-go-v2/service/dynamodb"
    "github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
)

func ShowProfile(c buffalo.Context) error {
    svc := c.Value("dynamodb").(*dynamodb.Client)
    // authenticated subject from session or JWT
    subjectID := c.Session().GetString("user_id")
    if subjectID == "" {
        return c.Error(http.StatusUnauthorized, errors.New("unauthenticated"))
    }
    // resource identifier from route
    userID := c.Param("user_id")
    // enforce ownership: subject must match requested user
    if subjectID != userID {
        return c.Error(http.StatusForbidden, errors.New("access denied"))
    }
    out, err := svc.GetItem(c.Request().Context(), &dynamodb.GetItemInput{
        TableName: aws.String("UserProfiles"),
        Key: map[string]types.AttributeValue{
            "user_id": &types.AttributeValueMemberS{Value: userID},
        },
    })
    if err != nil {
        return c.Error(http.StatusInternalServerError, err)
    }
    if out.Item == nil {
        return c.Render(http.StatusNotFound, r.JSON(map[string]string{"error": "not found"}))
    }
    return c.Render(http.StatusOK, r.JSON(out.Item))
}

When using GSIs, scope queries with the subject’s organization or tenant attribute to prevent cross-tenant reads:

// handlers/org_data.go
package handlers

import (
    "context"
    "net/http"

    "github.com/gobuffalo/buffalo"
    "github.com/aws/aws-sdk-go-v2/service/dynamodb"
    "github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
)

func ListOrgItems(c buffalo.Context) error {
    svc := c.Value("dynamodb").(*dynamodb.Client)
    orgID := c.Session().GetString("org_id")
    subjectID := c.Session().GetString("user_id")
    if orgID == "" || subjectID == "" {
        return c.Error(http.StatusUnauthorized, errors.New("unauthenticated"))
    }
    // Ensure subject belongs to orgID (e.g., via a membership table) before querying
    out, err := svc.Query(c.Request().Context(), &dynamodb.QueryInput{
        TableName: aws.String("OrgItems"),
        IndexName: aws.String("OrgGSI"),
        KeyConditionExpression: aws.String("org_id = :org_val"),
        ExpressionAttributeValues: map[string]types.AttributeValue{
            ":org_val": &types.AttributeValueMemberS{Value: orgID},
        },
        Limit: aws.Int32(50),
    })
    if err != nil {
        return c.Error(http.StatusInternalServerError, err)
    }
    return c.Render(http.StatusOK, r.JSON(out.Items))
}

Additionally, avoid exposing raw DynamoDB keys in URLs when possible; use indirect references mapped server-side. Combine these practices with centralized authorization logic (e.g., a permission service) to keep ownership checks consistent across Buffalo handlers. Remember that middleBrick can validate your API’s exposed surface by scanning endpoints for missing authorization patterns; the Pro plan’s continuous monitoring can alert you if a new route lacks these checks.