Vulnerable Components in Fiber with Mongodb
Vulnerable Components in Fiber with Mongodb — how this specific combination creates or exposes the vulnerability
When building APIs with Fiber and MongoDB, several common patterns introduce security weaknesses that middleBrick detects as part of its 12 security checks. Because Fiber is a fast, unopinionated web framework and MongoDB is a flexible, schema-less database, developers must explicitly enforce validation, authorization, and safe data handling. Without strict controls, endpoints can expose Insecure Direct Object References (IDOR), Broken Object Level Authorization (BOLA), and unsafe data consumption.
IDOR/BOLA and route parameters. In Fiber, route parameters such as :id are often bound directly to database queries. If a handler uses the parameter to construct a MongoDB filter without verifying that the requesting user has permission to access that document, an attacker can change the ID to access or modify other users’ data. middleBrick tests this by probing endpoints with different identifiers and inspecting whether authorization checks are enforced.
Input validation and NoSQL injection. Because MongoDB queries are built programmatically, unsanitized user input can alter query structure. For example, passing user-controlled objects into Find or Aggregate can lead to injection-like behavior, including field poisoning or bypassing intended filters. In a Fiber route, failing to validate and sanitize fields like filter or projection can expose sensitive fields or enable authentication bypass. middleBrick’s input validation checks look for unsafe deserialization and missing schema validation.
Excessive data exposure and projection mistakes. A frequent mistake is returning full MongoDB documents directly to clients, which may contain sensitive fields such as password hashes, tokens, or internal metadata. In Fiber, if a handler calls Find without specifying a projection to exclude sensitive keys, those fields are included in the HTTP response. middleBrick’s Data Exposure check scans responses for credentials, PII, and API keys to highlight these leaks.
Unsafe consumption of user-supplied data in update operations. Using Map or raw bson.M constructed from context.FormValue or JSON bodies without validation can allow an attacker to supply update operators like $set on fields they should not modify, or to inject unexpected operators that escalate privileges or corrupt data. This pattern maps to the BFLA/Privilege Escalation and Unsafe Consumption checks in middleBrick, which analyze whether update handlers enforce strict field allowlists.
Overly broad query filters in list endpoints. When an endpoint exposes query parameters that are forwarded directly to MongoDB, such as a search or filter interface, missing length and type checks can lead to unexpectedly large result sets or server-side resource exhaustion. middleBrick’s Rate Limiting and Inventory Management checks look for missing pagination and unbounded queries that can degrade availability.
LLM/AI Security in API workflows. If your Fiber service returns data to LLM-based clients or uses LLM-generated content derived from MongoDB documents, middleBrick’s LLM/AI Security checks detect System Prompt Leakage, prompt injection attempts, and outputs containing API keys or PII. This is especially relevant when model responses include data retrieved from or influenced by database content.
Mongodb-Specific Remediation in Fiber — concrete code fixes
Remediation centers on explicit allowlists, strict validation, and separation of concerns between route parameters and database logic. The following examples assume you are using the official MongoDB Go driver and have a user context that identifies the requester.
1. Enforce ownership checks with ID validation. Always resolve the requesting user’s identity from authentication (e.g., JWT) and include it in the filter. Do not rely solely on the route parameter.
import (
"context"
"github.com/gofiber/fiber/v2"
"go.mongodb.org/mongo-driver/bson"
"go.mongodb.org/mongo-driver/mongo"
)
func GetUserProfile(c *fiber.Ctx) error {
userID := c.Params("id")
// authenticatedID comes from your auth middleware
authenticatedID, ok := c.Locals("userID").(string)
if !ok || userID != authenticatedID {
return c.Status(fiber.StatusForbidden).JSON(fiber.Map{"error": "access denied"})
}
var profile UserProfile
filter := bson.M{"_id": userID, "owner_id": authenticatedID}
err := usersCollection.FindOne(c.Context(), filter).Decode(&profile)
if err != nil {
return c.Status(fiber.StatusNotFound).JSON(fiber.Map{"error": "not found"})
}
return c.JSON(profile)
}
2. Validate and sanitize input before building queries. Use structured input types and server-side validation instead of passing raw maps from the client.
import "github.com/go-playground/validator/v10"
type SearchParams struct {
Email string `validate:"required,email"`
Limit int `validate:"min=1,max=50"`
}
func SearchUsers(c *fiber.Ctx) error {
var p SearchParams
if err := c.BodyParser(&p); err != nil {
return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "invalid payload"})
}
validate := validator.New()
if err := validate.Struct(p); err != nil {
return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": err.Error()})
}
cursor, err := usersCollection.Find(c.Context(), bson.M{"email": p.Email})
if err != nil {
return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": "search failed"})
}
var results []UserProfile
if err = cursor.All(c.Context(), &results); err != nil {
return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": "decoding failed"})
}
return c.JSON(results)
}
3. Use projections to limit returned fields. Never return full documents when only a subset is needed.
func GetPublicProfile(c *fiber.Ctx) error {
userID := c.Params("id")
var result struct {
ID string `bson:"_id"`
Name string `bson:"name"`
Email string `bson:"email"`
}
err := usersCollection.FindOne(c.Context(),
bson.M{"_id": userID},
mongo.FindOneAndUpdateOptions{Projection: bson.D{{"name", 1}, {"email", 1}, {"_id", 1}}},
).Decode(&result)
if err != nil {
return c.Status(fiber.StatusNotFound).JSON(fiber.Map{"error": "not found"})
}
return c.JSON(result)
}
4. Whitelist allowed update operators and fields. Reject raw user input that could contain update operators like $set on sensitive paths.
type UpdateProfileRequest struct {
DisplayName *string `json:"displayName"`
Bio *string `json:"bio"`
}
func UpdateProfile(c *fiber.Ctx) error {
userID, ok := c.Locals("userID").(string)
if !ok {
return c.SendStatus(fiber.StatusUnauthorized)
}
var req UpdateProfileRequest
if err := c.BodyParser(&req); err != nil {
return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "invalid body"})
}
updateFields := bson.M{}
if req.DisplayName != nil {
updateFields["profile.displayName"] = *req.DisplayName
}
if req.Bio != nil {
updateFields["profile.bio"] = *req.Bio
}
if len(updateFields) == 0 {
return c.SendStatus(fiber.StatusBadRequest)
}
_, err := usersCollection.UpdateOne(
c.Context(),
bson.M{"_id": userID},
bson.M{"$set": updateFields},
)
if err != nil {
return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": "update failed"})
}
return c.SendStatus(fiber.StatusOK)
}
5. Apply pagination and limits to list endpoints. Prevent unbounded queries by enforcing page and size parameters with strict boundaries.
func ListItems(c *fiber.Ctx) error {
page := c.QueryInt("page", 1)
size := c.QueryInt("size", 20)
if page < 1 || size < 1 || size > 100 {
return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "invalid pagination"})
}
cursor, err := itemsCollection.Find(c.Context(),
bson.M{},
options.Find().SetSkip(int64((page - 1) * size)).SetLimit(size),
)
if err != nil {
return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": "failed to list"})
}
var results []Item
if err = cursor.All(c.Context(), &results); err != nil {
return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": "decoding failed"})
}
return c.JSON(results)
}