Need

Ensure data authenticity through proper checksum verification

Context

• Usage of Scala for building scalable and functional applications
• Usage of play.api.libs.ws for making HTTP requests in a Play Framework application

Description

Non compliant code

        import play.api.libs.ws._

val ws: WSClient

def fetchResource(url: String) = {
  val futureResponse: Future[WSResponse] = ws.url(url).get()
  futureResponse.map { response =>
    // Process the response
    val resourceData = response.body
    // Do something with the resourceData
  }
}
        
        

The above Scala code represents a function fetchResource in a Play framework application that fetches resources from an external server using a GET request. The ws.url(url).get() function is used to send a GET request to the specified URL, and the response is processed to extract the resource data.

However, this code is vulnerable due to insufficient data authenticity validation. Specifically, it does not validate the integrity of the loaded resources, which means it does not check whether the data has been tampered with during transmission.

This vulnerability can lead to serious security issues. For instance, an attacker could intercept the request and modify the resource data, leading to the application processing incorrect or malicious data.

The proper way to mitigate this vulnerability is to implement a checksum verification mechanism. This involves generating a checksum for the original data on the server side, transmitting this checksum along with the data, and then comparing this checksum with the checksum generated from the received data on the client side. If the two checksums match, it can be assumed that the data has not been tampered with during transmission.

Steps

• Implement data authenticity validation by verifying the checksum of the resource.
• Retrieve the checksum of the resource from a trusted source.
• Calculate the checksum of the downloaded resource.
• Compare the calculated checksum with the trusted checksum.
• If the checksums match, proceed with processing the resource.
• If the checksums do not match, consider the resource as potentially compromised and handle accordingly.

Compliant code

        import play.api.libs.ws._
import java.security.MessageDigest
import scala.concurrent.ExecutionContext.Implicits.global

val ws: WSClient

def fetchResource(url: String, trustedChecksum: String) = {
  val futureResponse: Future[WSResponse] = ws.url(url).get()
  futureResponse.map { response =>
    // Process the response
    val resourceData = response.body
    // Calculate the checksum of the downloaded resource
    val md = MessageDigest.getInstance("SHA-256")
    val calculatedChecksum = md.digest(resourceData.getBytes("UTF-8")).map("%02x".format(_)).mkString
    // Compare the calculated checksum with the trusted checksum
    if (calculatedChecksum == trustedChecksum) {
      // Checksums match, proceed with processing the resource
      // Do something with the resourceData
    } else {
      // Checksums do not match, consider the resource as potentially compromised
      // Handle accordingly
    }
  }
}
        
        

The updated code now includes a checksum verification process to validate the integrity of the downloaded resource.

The fetchResource function now takes an additional parameter trustedChecksum, which is the checksum of the resource from a trusted source.

After the resource is downloaded, the code calculates the checksum of the resource using the SHA-256 algorithm. This is done by creating a MessageDigest instance for SHA-256 and then digesting the resource data bytes. The digested bytes are then converted to a hexadecimal string to form the calculated checksum.

The calculated checksum is then compared with the trusted checksum. If they match, the resource is considered authentic and processing of the resource continues. If they do not match, the resource is considered potentially compromised and should be handled accordingly.

This update ensures that the application properly validates the integrity of resources loaded from external servers, thus fixing the vulnerability.

References

• 355. Insufficient data authenticity validation - Checksum verification