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Lack of data validation - Content Spoofing

Need​

Implementation of robust data validation and authentication mechanisms

Context​

  • Usage of Scala 2.12 for developing scalable and high-performance applications
  • Usage of play.api.mvc for handling HTTP requests and building web applications in the Play Framework
  • Usage of play.api.libs.Files for file handling in Play Framework
  • Usage of java.nio.file.Paths for working with file paths in Java

Description​

Non compliant code​

import play.api.mvc._
import play.api.libs.Files._

def upload = Action(parse.multipartFormData) { request =>
  request.body.file("picture").map { picture =>
    val filename = picture.filename
    val contentType = picture.contentType
    picture.ref.moveTo(Paths.get(s"/user/files/$filename"), replace = true)
    Ok("File uploaded")
  }.getOrElse {
    Redirect(routes.Application.index).flashing(
      "error" -> "Missing file"
    )
  }
}

The above code snippet is a simple file upload handler in a Play Framework application written in Scala.

The function upload is an action that handles multipart form data. It extracts the file from the form data with the field name "picture". If the file is present, it moves the file to a new location in the server's filesystem with the filename extracted from the uploaded file. The replace = true option in the move function allows the newly uploaded file to overwrite any existing file with the same name.

The vulnerability in this code lies in the lack of validation of the uploaded file. There are two main issues:

  1. Lack of data validation: The application does not validate the contents of the uploaded file. An attacker could upload a malicious file which could lead to various security issues.

  2. Content Spoofing: Since the application does not validate if a file with the same name already exists, an attacker can replace an existing file by uploading a new file with the same name. This could be used to replace legitimate files with malicious ones, leading to content spoofing attacks.

To mitigate these vulnerabilities, the application should validate the contents of the uploaded file to ensure it is of the expected type and does not contain any malicious content. In addition, the application should check if a file with the same name already exists before moving the uploaded file, and either prevent the upload or generate a new, unique filename.

Steps​

  • Implement authentication and authorization mechanisms to ensure that only authorized users can upload files.
  • Validate the file upload request to ensure that the file being uploaded is not already present in the server.
  • Implement file name and content type validation to prevent spoofing attacks.
  • Store uploaded files in a secure location outside of the web root directory to prevent direct access.
  • Consider implementing file versioning or unique file identifiers to prevent overwriting of existing files.

Compliant code​

import play.api.mvc._
import play.api.libs.Files._
import java.nio.file.{Files, Paths}
import java.security.MessageDigest

def upload = Action(parse.multipartFormData) { request =>
  request.body.file("picture").map { picture =>
    val filename = picture.filename
    val contentType = picture.contentType
    val path = Paths.get(s"/secure/files/$filename")
    if (Files.exists(path)) {
      BadRequest("File already exists")
    } else {
      val digest = MessageDigest.getInstance("SHA-256")
      val hash = digest.digest(filename.getBytes(StandardCharsets.UTF_8))
      val hashedFilename = String.format("%064x", new BigInteger(1, hash))
      picture.ref.moveTo(Paths.get(s"/secure/files/$hashedFilename"), replace = false)
      Ok("File uploaded")
    }
  }.getOrElse {
    Redirect(routes.Application.index).flashing(
      "error" -> "Missing file"
    )
  }
}

The updated code includes several security enhancements to address the identified vulnerability:

  1. File Existence Check: Before moving the file, the code checks if a file with the same name already exists in the server. If it does, the server responds with a BadRequest status, indicating that the file already exists.

  2. Secure File Storage: The files are stored in a /secure/files/ directory, which should be located outside of the web root directory. This prevents direct access to the uploaded files.

  3. Unique File Identifiers: To prevent overwriting of existing files, the code generates a unique SHA-256 hash of the filename. This hash is used as the new filename when the file is moved to the secure directory. This ensures that even if two files have the same original name, they will not overwrite each other in the server.

Please note that this code does not include authentication and authorization mechanisms. These should be implemented separately to ensure that only authorized users can upload files. Additionally, you should validate the file name and content type to prevent spoofing attacks.

References​

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