Email Injection in Aspnet with Cockroachdb

Email Injection occurs when user-controlled data is concatenated into email headers or commands without validation, enabling an attacker to inject additional headers such as CC, BCC, or subject lines. In an Aspnet application that uses Cockroachdb as the backend, the risk emerges from two layers: the web framework’s handling of email-related input and the database interaction patterns used to store or retrieve that input.

In Aspnet, model binding often maps HTTP request fields directly to action parameters. If an email field (e.g., To, Cc, or Subject) is bound from user input and later passed to a service that builds email commands or queries, unsanitized newlines (CRLF, %0D%0A, or Unicode line separators) can break header structure. Cockroachdb, while PostgreSQL-wire compatible, does not sanitize these payloads; it stores them as provided. When the stored values are later used in email-sending logic (for example, in a background worker that reads email destinations from a Cockroachdb table), the injected header commands can alter the routing or recipients of the message.

The combination amplifies impact because Cockroachdb’s JSON and string columns may retain multi-line input exactly as submitted. If the Aspnet layer trusts these stored values when composing emails (for instance, using SmtpClient or a third-party mail library), the injected headers can lead to unintended recipients, header smuggling, or even server-side request forgery depending on how the mail transaction is constructed. In a black-box scan, middleBrick tests this attack surface by probing endpoints that accept and later use email fields, checking whether newline characters in stored Cockroachdb values result in additional headers in the outbound message.

From a compliance perspective, this maps to OWASP API Top 10 #6: Security Misconfiguration and #7: Injection. Although middleBrick does not fix the issue, its reports highlight these findings with severity ratings and remediation guidance, helping teams prioritize input validation and output encoding.

Remediation focuses on strict validation and canonicalization of email inputs before they reach Cockroachdb, and safe handling when reading values for email composition. The following practices reduce the attack surface.

• Validate email fields on the server using Aspnet’s built-in mechanisms and explicit regex patterns that exclude control characters and line breaks.
• Encode headers when constructing messages; avoid concatenating raw user input into header strings.
• Use parameterized queries to avoid secondary injection vectors when persisting or retrieving email-related data.

Example: Aspnet model with validation and a repository that safely stores and retrieves data from Cockroachdb using Npgsql.

using System.ComponentModel.DataAnnotations;
using Npgsql;

public class ContactMessage
{
    [Required]
    [EmailAddress]
    [RegularExpression(@"^[^\r\n]+$", ErrorMessage = "Newlines are not allowed.")]
    public string To { get; set; }

    [EmailAddress]
    [RegularExpression(@"^[^\r\n]+$", ErrorMessage = "Newlines are not allowed.")]
    public string Cc { get; set; }
}

public class EmailRepository
{
    private readonly string _connectionString;

    public EmailRepository(string connectionString) => _connectionString = connectionString;

    public void StoreMessage(ContactMessage message)
    {
        const string sql = "INSERT INTO contact_messages (to_addr, cc_addr, created_at) VALUES (@to, @cc, NOW())";
        using var conn = new NpgsqlConnection(_connectionString);
        conn.Open();
        using var cmd = new NpgsqlCommand(sql, conn);
        cmd.Parameters.AddWithValue("@to", message.To);
        cmd.Parameters.AddWithWithValue("@cc", message.Cc ?? DBNull.Value.ToString());
        cmd.ExecuteNonQuery();
    }

    public ContactMessage GetById(int id)
    {
        const string sql = "SELECT to_addr, cc_addr FROM contact_messages WHERE id = @id";
        using var conn = new NpgsqlConnection(_connectionString);
        conn.Open();
        using var cmd = new NpgsqlCommand(sql, conn);
        cmd.Parameters.AddWithValue("@id", id);
        using var reader = cmd.ExecuteReader();
        if (reader.Read())
        {
            return new ContactMessage
            {
                To = reader.GetString(0),
                Cc = reader.IsDBNull(1) ? null : reader.GetString(1)
            };
        }
        return null;
    }
}

When sending email, avoid building headers via string concatenation. Instead, use Aspnet’s MailMessage and SmtpClient (or modern alternatives) which handle encoding safely:

using System.Net;
using System.Net.Mail;

public class EmailService
{
    public void Send(ContactMessageSafe model)
    {
        var message = new MailMessage();
        message.From = new MailAddress("noreply@example.com");
        // Safe: Add method parses addresses and does not interpret control characters as headers
        message.To.Add(model.To);
        if (!string.IsNullOrEmpty(model.Cc))
        {
            message.Cc.Add(model.Cc);
        }
        message.Subject = "Contact request";
        message.Body = "A new contact message has been submitted.";

        using var client = new SmtpClient("smtp.example.com")
        {
            Port = 587,
            Credentials = new NetworkCredential("user", "pass"),
            EnableSsl = true,
        };
        client.Send(message);
    }
}

public class ContactMessageSafe
{
    public string To { get; set; }
    public string Cc { get; set; }
}

For continuous protection in pipelines, the middleBrick CLI can be integrated to scan Aspnet endpoints and detect whether email-related inputs reflect stored Cockroachdb values without proper sanitization. Findings include precise remediation steps and mapping to frameworks such as OWASP API Top 10.