CVE-2026-41319 MailKit STARTTLS响应注入漏洞

/* * Conceptual PoC for STARTTLS Response Injection * This script demonstrates how a MITM can inject data before TLS. */ // Simulating the vulnerable flow in MailKit before 4.16.0 // 1. Client reads data into buffer (Attacker injects here) // 2. Client calls StartTls() // 3. Internal Stream is replaced by SslStream // 4. Buffer is NOT flushed (Vulnerability) // 5. Client reads from buffer, getting Attacker's injected response using System; using System.IO; using System.Net.Sockets; using System.Text; public class VulnerableSmtpClient { Stream networkStream; Stream tlsStream; StringBuilder readBuffer = new StringBuilder(); // Simulating internal buffer public void Connect(string host, int port) { var tcp = new TcpClient(host, port); networkStream = tcp.GetStream(); } // Simulating the read operation that buffers data public string ReadResponse() { // In a real attack, MITM injects "SASL PLAIN" here before TLS byte[] buffer = new byte[1024]; int bytesRead = networkStream.Read(buffer, 0, buffer.Length); string response = Encoding.UTF8.GetString(buffer, 0, bytesRead); readBuffer.Append(response); // Data stays in buffer return response; } public void StartTls() { // Upgrade stream tlsStream = new SslStream(networkStream); ((SslStream)tlsStream).AuthenticateAsClient("example.com"); // VULNERABILITY: readBuffer is not cleared here // The injected data from 'networkStream' is still in 'readBuffer' } public string ReadPostTlsResponse() { // Client expects data from TLS stream, but gets buffered injected data if (readBuffer.Length > 0) { string data = readBuffer.ToString(); readBuffer.Clear(); return data; // Returns injected data thinking it's from secure server } // Read actual TLS data... return ""; } }