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Symmetric denial of service - SMTP

Description​

The server crashes with multiple requests to the SMTP service that is responsible for testing the sending of emails, since the txtEmail attribute does not validate the number of emails or characters that can be entered.

Impact​

Cause a denial of service.

Recommendation​

Define a character or email limit for the txtEmail field.

Threat​

Authenticated Internet attacker.

Expected Remediation Time​

⌚ 60 minutes.

Score​

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

Base​

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

Temporal​

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

Result​

  • Vector string: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H/E:X/RL:X/RC:X
  • Score:
    • Base: 6.5
    • Temporal: 6.5
  • Severity:
    • Base: Medium
    • Temporal: Medium

Code Examples​

Compliant code​

All input data is correctly verified on the server side

public static void Test(string server, string txtEmail) {
  string to = "user";
  string from = "user";
  //Validate the txtEmail input field
  string sanitizedEmail = checkTxtEmailInput(txtEmail);
  MailMessage message = new MailMessage(from, to, sanitizedEmail);
  message.Subject = "Subject";
  message.Body = @"Body";
  SmtpClient client = new SmtpClient(server);
  client.UseDefaultCredentials = true;
  client.EnableSsl = true;
  client.Send(message);
}

Non compliant code​

The application does not perform server side validation of some input data

public static void Test(string server, string txtEmail) {
  string to = "user";
  string from = "user";
  //Create Message without validating length or number of emails
  MailMessage message = new MailMessage(from, to, txtEmail);
  message.Subject = "Subject";
  message.Body = @"Body";
  SmtpClient client = new SmtpClient(server);
  client.UseDefaultCredentials = true;
  client.EnableSsl = true;
  client.Send(message);
}

Requirements​

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