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External control of file name or path

Description​

It is possible to modify the path to which an uploaded file will be saved.

Impact​

  • Save files in paths other than those expected by the application.
  • Overwrite important files within the system by referring to the path where the upload is performed.

Recommendation​

Validate uploaded files names on the system and restrict the storage to destined folders only.

Threat​

Anonymous attacker from external network.

Expected Remediation Time​

⌚ 30 minutes.

Score​

Default score using CVSS 3.1. It may change depending on the context of the vulnerability.

Base​

  • Attack vector: N
  • Attack complexity: H
  • Privileges required: L
  • User interaction: N
  • Scope: U
  • Confidentiality: N
  • Integrity: L
  • Availability: N

Temporal​

  • Exploit code madurity: P
  • Remediation level: X
  • Report confidence: X

Result​

  • Vector string: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N/E:P/RL:X/RC:X
  • Score:
    • Base: 3.1
    • Temporal: 3.0
  • Severity:
    • Base: Low
    • Temporal: Low

Code Examples​

Compliant code​

User input is validated on the server side before granting access to a file

using System;
using System.IO;
public partial class WebForm : System.Web.UI.Page {
  protected void Page_Load(object sender, EventArgs e) {
    string userInput = clearInput(Request.Params["UserInput"]);
    string verifiedFilePath = "/myTrustedPath"
    var elem = File.Open(userInput, verifiedFilePath,  FileMode.Open);
  }
}

Non compliant code​

User input is not validated before opening a file

using System;
using System.IO;
public partial class WebForm : System.Web.UI.Page {
  protected void Page_Load(object sender, EventArgs e) {
    string userInput = Request.Params["UserInput"];
    stirng filePath = userInput.path;
    var elem = File.Open(userInput, filePath,  FileMode.Edit);
  }
}

Requirements​