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Lack of data validation - Header x-amzn-RequestId

Need​

Implementation of strict data validation for the x-amzn-RequestId Header

Context​

  • Usage of Go 1.16 for building efficient and scalable applications
  • Usage of Gin for building web applications in Go

Description​

Non compliant code​

package main

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

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

    r.POST("/data", func(c *gin.Context) {
        xAmznRequestId := c.GetHeader("x-amzn-RequestId")
        // process the request with the xAmznRequestId
    })

    r.Run()
}

In the code above, the server is using the Gin framework to handle HTTP requests. In the POST route handler for "/data", it is attempting to retrieve the value of the "x-amzn-RequestId" header from the request context.

The vulnerability lies in the fact that there is no validation performed on the value of the "x-amzn-RequestId" header. This means that a malicious user could potentially pass in a dangerous character string via this header, which could lead to various types of attacks such as SQL Injection, Cross-Site Scripting (XSS), or Remote Code Execution (RCE), depending on how the server uses this header value.

In addition, the server does not control server-side permission to modify certain fields, including the "x-amzn-RequestId" header. This means that a malicious user could potentially modify this header value in a way that could compromise the server's security or functionality.

To mitigate this vulnerability, the server should implement input validation for the "x-amzn-RequestId" header value, and control server-side permission to modify this header.

Steps​

  • Implement server-side validation for the x-amzn-RequestId header.
  • Define a whitelist of allowed characters for the x-amzn-RequestId header.
  • Reject or sanitize any input that contains potentially dangerous characters.
  • Use regular expressions or string manipulation functions to validate the input.
  • Consider using a middleware to handle the validation logic for all routes.
  • Return an appropriate error response if the input is invalid.

Compliant code​

package main

import (
    "github.com/gin-gonic/gin"
    "net/http"
    "regexp"
)

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

    r.Use(validateRequestId())

    r.POST("/data", func(c *gin.Context) {
        xAmznRequestId := c.GetHeader("x-amzn-RequestId")
        // process the request with the xAmznRequestId
    })

    r.Run()
}

func validateRequestId() gin.HandlerFunc {
    return func(c *gin.Context) {
        xAmznRequestId := c.GetHeader("x-amzn-RequestId")
        match, _ := regexp.MatchString("^[a-zA-Z0-9-]*$", xAmznRequestId)
        if !match {
            c.JSON(http.StatusBadRequest, gin.H{"error": "Invalid x-amzn-RequestId header"})
            c.Abort()
            return
        }
        c.Next()
    }
}

The updated code includes a middleware function validateRequestId() that validates the x-amzn-RequestId header for every request. This function is added to the Gin engine using the Use() function, which applies it to all routes.

The validateRequestId() function retrieves the x-amzn-RequestId header from the request context and checks it against a regular expression. The regular expression ^[a-zA-Z0-9-]*$ only allows alphanumeric characters and hyphens. This is a common pattern for request IDs, but you should adjust it according to your specific requirements.

If the x-amzn-RequestId header does not match the regular expression, the function responds with a 400 Bad Request status and an error message. It also calls c.Abort() to prevent further processing of the request.

If the x-amzn-RequestId header is valid, the function calls c.Next() to allow the next handler in the chain to process the request.

This approach ensures that all requests have a valid x-amzn-RequestId header before they are processed by your application. It helps to prevent injection attacks and other security vulnerabilities related to unvalidated input.

References​

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