Nosql Injection in Buffalo with Bearer Tokens

Buffalo is a web framework for Go that encourages structure and security best practices. When an endpoint accepts a Bearer Token from an Authorization header and uses request-derived values to build NoSQL queries (for example, MongoDB or Couchbase), the combination can expose injection risks if the input is not strictly validated. A common pattern is to extract the token and use it to scope database queries, such as filtering records by owner ID extracted from the token claims. If the application directly interpolates user-controlled parameters into the query without proper handling, an attacker can manipulate the query logic through injection.

Consider an endpoint that retrieves a user’s profile. The Bearer Token is parsed to obtain a user ID, which is then used to filter documents. If an attacker supplies a malformed query parameter that alters the constructed query, they may be able to bypass intended filters or read other users’ data. For instance, if the query is built using string concatenation or an unsafe DSL, a specially crafted parameter could change the semantics of the query. This can lead to unauthorized access to other users’ data or enumeration of resources, which aligns with BOLA/IDOR findings that middleBrick detects during its 12 security checks.

During a scan, middleBrick tests the unauthenticated attack surface and the authenticated surface when tokens are supplied. It checks for improper query construction, missing validation on parameters used in NoSQL filters, and whether the token is treated as an immutable identifier that cannot be overridden by user input. The tool’s LLM/AI Security checks do not apply directly here, but the authentication and BOLA/IDOR assessments highlight whether the token is correctly used to enforce ownership boundaries. A finding may indicate that the application does not enforce strict schema validation on query inputs, allowing an attacker to inject operators such as $where or manipulate JSON paths to escape intended filters.

Real-world examples include the use of regex patterns that inadvertently allow injection or the use of framework helpers that do not sanitize nested fields. For instance, if a query uses a map function that dynamically includes keys from user input, an attacker might supply a key like __proto__ or use dot notation to traverse object boundaries. middleBrick’s property authorization checks help identify whether field-level permissions are consistently enforced across the API surface, which is especially important when tokens are used to scope data access.

Because Buffalo applications often rely on structured data formats, developers must ensure that NoSQL queries are built using typed structures and strict validation rather than string manipulation. The framework provides middleware for authentication, but it is the developer’s responsibility to bind the token’s claims to query filters safely. middleBrick’s scan results can map findings to relevant compliance frameworks such as OWASP API Top 10, highlighting A01:2023 Broken Object Level Authorization that may arise from weak token-to-query binding.

Remediation focuses on strict validation, parameterized queries, and avoiding direct concatenation of user input into NoSQL filters. When using Bearer Tokens in Buffalo, extract claims early and use them to construct query arguments that are passed as values, not as part of the query structure. Below are concrete code examples demonstrating safe patterns.

Example 1: Safe query construction with a Bearer Token

Assume the token contains a subject claim (sub) representing the user ID. Use this to filter records without allowing user parameters to modify the filter logic.

import (
    "github.com/gobuffalo/buffalo"
    "github.com/gobuffalo/packd"
    "go.mongodb.org/mongo-driver/bson"
    "net/http"
)

func GetUserProfile(c buffalo.Context) error {
    tokenString := c.Request().Header.Get("Authorization")
    if len(tokenString) < 7 || tokenString[:7] != "Bearer " {
        return c.Error(http.StatusUnauthorized, errors.New("missing or invalid bearer token"))
    }
    tokenString = tokenString[7:]

    claims, err := parseTokenClaims(tokenString) // returns map or struct with sub
    if err != nil {
        return c.Error(http.StatusUnauthorized, errors.New("invalid token"))
    }
    userID, ok := claims["sub"].(string)
    if !ok || userID == "" {
        return c.Error(http.StatusBadRequest, errors.New("invalid user identifier"))
    }

    // Safe: using userID as a value, not concatenated into the query string
    filter := bson.M{"user_id": userID, "deleted": false}
    var profile Profile
    err = db.Collection("profiles").FindOne(c.Request().Context(), filter).Decode(&profile)
    if err != nil {
        return c.Error(http.StatusNotFound, errors.New("profile not found"))
    }
    return c.Render(http.StatusOK, r.JSON(profile))
}

func parseTokenClaims(token string) (map[string]interface{}, error) {
    // Implement proper JWT parsing and validation
    return map[string]interface{}{"sub": "user-123"}, nil
}

Example 2: Validating and using query parameters with token-based scoping

If the endpoint accepts an additional parameter (e.g., profile_id), ensure it is validated and combined with the token-derived filter using an AND condition, never by altering the token filter.

func GetSharedProfile(c buffalo.Context) error {
    tokenString := c.Request().Header.Get("Authorization")
    // token extraction as above...

    profileID := c.Param("profile_id")
    if !isValidID(profileID) {
        return c.Error(http.StatusBadRequest, errors.New("invalid profile ID format"))
    }

    // Combine token scope with parameter using AND; do not embed parameter in the token filter logic
    filter := bson.M{
        "user_id":   userIDFromToken,
        "profile_id": profileID,
        "active":    true,
    }
    var details SharedProfile
    if err := db.Collection("shared_profiles").FindOne(c.Request().Context(), filter).Decode(&details); err != nil {
        return c.Error(http.StatusNotFound, errors.New("resource not accessible"))
    }
    return c.Render(http.StatusOK, r.JSON(details))
}

func isValidID(id string) bool {
    // Use a strict pattern, e.g., hex string of fixed length
    return len(id) == 24 && regexp.MustCompile(`^[a-f0-9]+$`).MatchString(id)
}

General remediation checklist

• Always treat the Bearer Token as an authentication scope, not as a query modifier.
• Use typed, parameterized queries and avoid string interpolation of user input into database filters.
• Validate and sanitize all incoming parameters independently before combining them with token-derived values.
• Apply principle of least privilege: ensure the token’s claims do not grant broader access than necessary.
• Leverage middleware to centralize token parsing and attach user context securely to the request.

By following these patterns, developers reduce the risk of NoSQL injection and BOLA/IDOR issues. middleBrick’s scans can verify that such controls are in place by checking authentication handling, property authorization, and input validation across the API surface.