Need

Implementation of input length validation

Context

• Usage of Go 1.16 for building high-performance and scalable applications
• Usage of gin-gonic/gin for building web applications and APIs in Go

Description

Non compliant code

        package main

import (
	"github.com/gin-gonic/gin"
)

func main() {
	r := gin.Default()

	r.POST("/endpoint", func(c *gin.Context) {
		var json struct {
			Data string `json:"data"`
		}

		if c.Bind(&json) == nil {
			// process the data
		}
	})

	r.Run()
}
        
        

The above code represents a simple POST endpoint in a Go application using the Gin framework. The /endpoint takes a JSON object with a data field in the request body and binds it to a local variable json.

The vulnerability lies in the lack of data validation on the length of the data field. The application does not check if the length of the data field exceeds a certain limit, thus allowing an attacker to send a massive amount of characters in the data field. This could potentially lead to various types of attacks such as Buffer Overflow, Denial of Service (DoS), and could also lead to other potential vulnerabilities due to the excessive processing of large amounts of data.

The application should always validate the length of the input data to prevent such vulnerabilities. This could be achieved by adding a simple length check before processing the data.

Steps

• Implement input length validation for the 'data' field in the JSON payload.
• Define a maximum allowed length for the 'data' field and check if the length of the input exceeds this limit.
• If the input length exceeds the limit, return an appropriate error response to the client.
• You can use the 'c.ShouldBindJSON' function to bind the JSON payload to the struct and validate the input length.
• Ensure that the error response does not reveal sensitive information about the application or its internals.

Compliant code

        package main

import (
	"github.com/gin-gonic/gin"
)

const MaxDataLength = 1000 // Define your maximum allowed length

func main() {
	r := gin.Default()

	r.POST("/endpoint", func(c *gin.Context) {
		var json struct {
			Data string `json:"data" binding:"required,max=1000"` // Add length validation
		}

		if err := c.ShouldBindJSON(&json); err != nil {
			c.JSON(400, gin.H{"error": "Data field is required and should not exceed 1000 characters"})
			return
		}

		// process the data
	})

	r.Run()
}
        
        

The updated code includes a length validation for the 'data' field in the JSON payload. This is done by adding a binding:"required,max=1000" tag to the 'Data' field in the struct. This tag tells Gin to bind the JSON payload to the struct and validate that the 'Data' field is present and does not exceed 1000 characters in length.

If the 'Data' field is missing or exceeds the maximum allowed length, the c.ShouldBindJSON(&json) function will return an error. In this case, the code returns a 400 status code and an error message to the client. The error message is generic and does not reveal any sensitive information about the application or its internals.

The MaxDataLength constant is used to define the maximum allowed length for the 'Data' field. This value can be adjusted according to the specific requirements of your application.

By implementing this length validation, the application is protected against attacks that involve sending massive amounts of characters to the endpoint.

References

• 194. Lack of data validation - Input Length