Email Injection in Cassandra

Email Injection in Cassandra-backed systems typically arises not from Cassandra itself—which is a database with no native email capabilities—but from application-layer patterns where email addresses or message content stored in Cassandra are later used in SMTP operations. The vulnerability manifests when an attacker submits malicious input via an API endpoint that accepts email-related parameters (e.g., email, contact, message), which the application then retrieves from Cassandra and incorporates into email headers or bodies without sanitization.

A common attack pattern involves inserting newline characters (\r\n) or other SMTP delimiters into input fields. For example, consider a user registration API that stores the email field in a Cassandra table. Later, a batch job reads this data to send welcome emails. If the stored email value contains injected headers, the SMTP server may interpret them as separate commands:

POST /api/v1/register
{
  "email": "attacker@example.com\r\nBCC: victim@company.com",
  "name": "Test"
}

In a vulnerable implementation, the application might construct an email message directly from the Cassandra-retrieved value:

String email = resultSet.getString("email");
String smtpCommand = "MAIL FROM:<" + email + ">\r
"; // Unsanitized concatenation

This could allow an attacker to add arbitrary recipients (BCC), modify subject lines, or even inject full MIME parts. In Cassandra-specific contexts, the risk is compounded if:

• Materialized Views or Secondary Indexes are used to query email fields, and injection payloads alter query logic (e.g., via CQL injection that modifies the view definition).
• User-Defined Functions (UDFs) written in Java or JavaScript process email data from Cassandra and directly interface with email libraries (e.g., JavaMail) without input validation.
• Triggers execute on table updates and send notifications using column values; an injected payload in a trigger’s SELECT or INSERT could propagate malicious content.

While Cassandra’s CQL itself is not vulnerable to traditional SQL injection when using parameterized queries, the danger lies in how application code handles data after retrieval from Cassandra, especially when that data feeds into external systems like SMTP servers. The attack surface is the API’s unvalidated input that persists in Cassandra and later participates in email composition.

Detecting Email Injection in Cassandra-integrated APIs requires probing endpoints that accept email-related input and observing how the system handles payloads containing SMTP metacharacters. middleBrick’s scanner automates this by sending sequential probes to API parameters likely to influence email generation (e.g., to, from, subject, body), then analyzing responses for indicators of successful injection.

The scanner checks for:

• Verbose Error Messages: Responses that leak SMTP server responses (e.g., 553 Invalid address) or reveal email routing details.
• Behavioral Changes: Variations in HTTP status codes or response bodies when payloads include \r\n sequences (e.g., a 200 OK instead of 400 Bad Request might indicate the payload was accepted and processed).
• Header Injection Artifacts: If the API echoes back user input or returns email-related metadata, injected headers may appear in the response (e.g., additional Bcc: fields).
• Time-Based Vectors: Payloads that trigger email-sending functions (e.g., attacker@example.com\r\nRCPT TO: victim@example.com) might cause delays or error patterns detectable via response timing.

Because middleBrick performs black-box scanning without database credentials, it cannot directly inspect Cassandra tables. Instead, it correlates API input points with downstream email functionality by:

1. Mapping API endpoints to potential email workflows via OpenAPI/Swagger spec analysis (e.g., parameters named email or operations tagged notifications).
2. Running active probes that simulate SMTP injection and monitoring for side effects like email delivery to attacker-controlled addresses (via callback URLs) or error messages that confirm SMTP command parsing.
3. Cross-referencing runtime findings with the OpenAPI spec to identify which Cassandra-backed parameters are most likely to be used in email contexts.

For example, a scan of an endpoint POST /api/v1/alerts with a recipient_email parameter might send a payload like test@test.com\r\nDATA\r\nSubject: Injected. If the response includes a string like SMTP 250 OK or the API returns an unexpected success, middleBrick flags this as a potential Email Injection vulnerability, mapping it to the Input Validation and Data Exposure categories.

Remediation focuses on securing the application layer that interacts with Cassandra, ensuring email-related data is validated and sanitized before storage and use. Cassandra itself offers no built-in email filtering, so defenses must be implemented in the code that reads from and writes to the database.

1. Input Validation at API Layer
Validate all email-related parameters against strict RFC 5322-compliant regex patterns before they reach Cassandra. Reject any input containing newline characters or SMTP command sequences.

// Example: Java Spring validation annotation
@Pattern(regexp = "^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$", message = "Invalid email format")
private String email;

2. Use Parameterized CQL Queries
Never concatenate user input into CQL strings. Use prepared statements to separate data from query structure, preventing injection that could alter query logic or store malicious payloads.

// Vulnerable: String concatenation
String cql = "INSERT INTO users (email) VALUES ('" + userEmail + "')";
session.execute(cql);

// Secure: Prepared statement
PreparedStatement ps = session.prepare("INSERT INTO users (email) VALUES (?)");
BoundStatement bs = ps.bind(userEmail);
session.execute(bs);

3. Sanitize Data Retrieved from Cassandra
Even with validated input, treat all data from Cassandra as untrusted when using it in email contexts. Strip or encode newline characters before including values in SMTP commands.

String sanitizedEmail = emailFromCassandra.replaceAll("\r|\n", "");
// Or use a library like Apache Commons Text to escape SMTP headers
String safeEmail = StringEscapeUtils.escapeCsv(emailFromCassandra);

4. Secure UDFs and Triggers
If using Cassandra UDFs (written in Java) that send emails, ensure they use parameterized inputs and validate data. Avoid UDFs that perform network operations like SMTP, as they execute within the Cassandra process and could amplify attacks.

// In a Java UDF: Never do this
public static void sendAlert(String email) {
  // Vulnerable: email used directly
  Transport.send(new MimeMessage(session, new InternetAddress(email)));
}

// Instead, validate and sanitize
public static void sendAlert(String email) {
  if (!email.matches("^[^\r\n]+@[^\r\n]+\.[^\r\n]+$")) {
    throw new IllegalArgumentException("Invalid email");
  }
  // Proceed with sanitized email
}

5. Defense in Depth
Configure your SMTP server to reject commands with unexpected newlines (e.g., Postfix’s smtpd_data_restrictions). Additionally, use middleware to log and alert on email fields containing \r\n patterns before they are stored in Cassandra.

These steps address the root cause: treating email-derived data as untrusted. By combining input validation, parameterized CQL, and output sanitization, you break the injection chain at both the storage (Cassandra) and retrieval (email composition) stages.

Email Injection in Cassandra ecosystems often flies under the radar because Cassandra lacks native email features. The vulnerability resides in the application logic that bridges Cassandra-stored data and email systems. An exploited injection could lead to:

• Spam Relay: Attackers abuse your SMTP server to send bulk spam, damaging your IP reputation.
• Data Exfiltration: Injected BCC headers redirect email content to attacker-controlled addresses.
• Account Takeover: Password reset emails might be redirected, enabling unauthorized access.
• Compliance Violations: Unauthorized data disclosure via email may breach GDPR, HIPAA, or PCI-DSS.

Because the malicious payload is stored in Cassandra, the attack can persist across sessions and affect multiple email operations (e.g., batch notifications, alerts). Scanning with a tool like middleBrick is essential to identify endpoints that accept email input and test for injection weaknesses before they are exploited.