Email Injection in Buffalo with Cockroachdb

Email Injection is a web security concern where attacker-controlled input is inserted into email headers or the message body, enabling header manipulation, spam relay, or phishing. In a Buffalo application using Cockroachdb as the backend, the risk arises when user-supplied data (such as name, reply-to address, or message fields) is incorporated into email workflows without strict validation and encoding. Because Cockroachdb is a PostgreSQL-compatible distributed database, the typical SQL interaction patterns in Buffalo involve parameterized queries; however, email generation often occurs in application code, not in the database layer, so improper handling of string concatenation before data reaches the email function can expose the application.

Buffalo applications commonly use the actions package and HTML template rendering to build forms that collect email-related inputs. If these inputs are passed directly to an email-sending helper (for example, using gomail or smtp libraries) without sanitization, an attacker can inject additional headers such as Cc:, Bcc:, or Subject:. In a Cockroachdb-driven backend, data is often stored first and then processed for notification emails. If stored data is later used to construct email headers, previously sanitized inputs might still lead to injection because encoding is applied at storage time but not at composition time. The database itself does not introduce the vulnerability, but its role as a persistent store means tainted data can remain available for future email generation, compounding the risk across sessions.

An illustrative attack flow in a Buffalo + Cockroachdb context: a user submits a contact form with a reply_to field containing newline characters and additional SMTP headers, which the application stores in Cockroachdb. Later, an automated notification job retrieves the stored value and uses it directly in an email header, resulting in injected Cc: or Reply-To: lines that redirect messages. Because Cockroachdb does not validate header syntax, the malicious payload persists until output encoding is enforced at the email composition layer. This cross-stage persistence highlights the need for context-aware encoding: database-safe strings are not necessarily email-safe strings.

Tools like middleBrick can help detect such issues by scanning the unauthenticated attack surface of a Buffalo API that interacts with Cockroachdb. For example, if the API exposes endpoints that store and later trigger email notifications based on user input, middleBrick’s checks for Input Validation and Unsafe Consumption can surface places where attacker-controlled data reaches email-generation code without proper sanitization. While middleBrick does not fix the issue, its findings include remediation guidance to implement strict allowlists for email headers and apply context-sensitive escaping before message construction.

Remediation focuses on ensuring that any data from Cockroachdb used in email headers is treated as an untrusted string and subjected to strict validation and encoding at the point of use. The following concrete steps and code examples show how to implement this in a Buffalo application.

• Validate and sanitize inputs at entry points: Use a strict allowlist for email header fields such as Reply-To and Subject. Accept only alphanumeric characters and a limited set of safe punctuation, rejecting newline characters and control characters.
• Use context-aware escaping when composing emails: Do not trust values retrieved from Cockroachdb. Apply encoding functions appropriate for the email library you use. For example, with net/smtp, ensure headers are encoded via mail.Header methods that handle folding and special characters.
• Separate storage from presentation: Store raw user input in Cockroachdb if necessary for auditing, but ensure that the data is transformed before inclusion in email headers. This prevents legacy data from automatically becoming exploitable.

Example: A Buffalo action that safely builds an email using a value stored in Cockroachdb.

// models/contact.go
package models
import "github.com/gobuffalo/pop/v6"

type Contact struct {
  ID        int64  `json:"id" db:"id"`
  ReplyName string `json:"reply_name" db:"reply_name"`
  ReplyAddr string `json:"reply_addr" db:"reply_addr"`
}

// actions/contacts.go
package actions
import (
  "fmt"
  "net/mail"
  "net/smtp"
  "strings"
  "your-app/models"
  "github.com/gobuffalo/buffalo"
  pop "github.com/gobuffalo/pop/v6"
)

func SendNotification(c buffalo.Context) error {
  tx := c.Value("tx").(*pop.Connection)
  var contact models.Contact
  // Retrieve a previously stored contact record from Cockroachdb
  if err := tx.Find(&contact, c.Param("id")); err != nil {
    return c.Render(500, r.JSON(map[string]string{"error": "server error"}))
  }
  // Validate and sanitize ReplyAddr before using it as a header value
  addr, err := mail.ParseAddress(fmt.Sprintf("%s <%s>", contact.ReplyName, contact.ReplyAddr))
  if err != nil {
    return c.Render(400, r.JSON(map[string]string{"error": "invalid contact address"}))
  }
  // Ensure no newline or control characters remain
  cleanName := strings.ReplaceAll(addr.Name, "\n", "")
  cleanAddr := strings.ReplaceAll(addr.Address, "\n", "")
  header := mail.Header{}
  header.Set("Reply-To", fmt.Sprintf("%s <%s>", cleanName, cleanAddr))
  // Compose and send email using smtp with the safe header
  msg := []byte("To: user@example.com\r\n" + header.String() + "\r\n\r\nHello, this is safe.\r\n")
  auth := smtp.PlainAuth("", "user@example.com", "password", "smtp.example.com")
  if err := smtp.SendMail("smtp.example.com:587", auth, "noreply@example.com", []string{"recipient@example.com"}, msg); err != nil {
    return c.Render(500, r.JSON(map[string]string{"error": "failed to send"}))
  }
  return c.Render(200, r.JSON(map[string]string{"status": "ok"}))
}

In this example, the values retrieved from Cockroachdb are parsed and reconstructed using mail.ParseAddress to ensure proper formatting, followed by replacement of newline characters to block header injection. The resulting header is set via mail.Header, which safely encodes special characters. This pattern enforces that data from the database is treated as opaque and never directly interpolated into email headers.