Mohammad Waseem

Posted on Feb 3

Rapid Validation of Email Flows in Rust: A Security Researcher's Approach Under Deadline Pressure

#rust #security #email

In security research, the ability to rapidly validate email flows is crucial for identifying vulnerabilities, ensuring compliance, and improving overall email security posture. This process becomes challenging under tight deadlines, especially when the existing tools and workflows are insufficient or overly complex. Leveraging Rust for this task offers a compelling balance of safety, performance, and expressiveness.

The Challenge

Imagine a scenario where a security researcher needs to verify the integrity of email delivery flows within a short span—say, 48 hours. The goal is to create a tool that can simulate, monitor, and validate email transactions across various mail servers, ensuring they follow expected patterns, and detecting anomalies such as spoofing, relay misuse, or misconfigurations.

Why Rust?

Rust's memory safety guarantees, combined with its high-performance utilities, make it ideal for network-heavy applications that require precision and reliability. Its extensive ecosystem, including crates for SMTP, networking, and asynchronous processing, accelerates development time—a vital factor when under deadline pressure.

Developing the Validation Tool

Step 1: Setting Up Dependencies

We start by choosing the right crates:

[dependencies]
async-std = { version = "1.10" }
smpt-auth = "0.4"
lettre = { version = "0.10", features = ["async_std"] }

Leveraging lettre, an asynchronous SMTP client, enables us to simulate email sending and receiving flows.

Step 2: Simulating Email Flow

The core functionality involves sending test emails and verifying their processing paths. Here's a snippet demonstrating asynchronous email dispatch:

use lettre::AsyncTransport;
use lettre::message::Message;
use lettre::AsyncSmtpTransport;
use lettre::Tokio1Executor;

#[tokio::main]
async fn main() {
    let email = Message::builder()
        .from("researcher@security.com".parse().unwrap())
        .to("target@domain.com".parse().unwrap())
        .subject("Validation Test")
        .body("This is a test email for validation.")
        .unwrap();

    let mailer = AsyncSmtpTransport::<Tokio1Executor>::relay("smtp.targetdomain.com")
        .unwrap()
        .build();

    let result = mailer.send(email).await;
    match result {
        Ok(_) => println!("Email sent successfully."),
        Err(e) => println!("Failed to send email: {}", e),
    }
}

This code sets up an async SMTP relay, dispatches a test message, and handles potential errors efficiently.

Step 3: Validating Email Flow

Beyond sending, the system must capture responses, analyze headers, and verify DKIM, SPF, and DMARC configurations. For instance, parsing headers:

use mailparse::*;

fn validate_headers(raw_email: &str) {
    let parsed = mailparse::parse_mail(raw_email.as_bytes()).unwrap();
    for header in parsed.headers.iter() {
        if header.get_key() == "Received" {
            println!("Received header: {}", header.get_value());
        }
        // Additional validation logic for DKIM, SPF, DMARC
    }
}

Automating checks for these headers helps identify if email inconsistencies suggest spoofing or misconfigurations.

Overcoming Deadline Constraints

In urgent scenarios, rapid prototyping by leveraging Rust’s async ecosystem minimizes the development cycle. Using crates like lettre and mailparse allows for building comprehensive validation tools with minimal custom implementation. Automated scripts can be integrated into CI pipelines, ensuring ongoing validation even post-deadline.

Final Thoughts

While the tight deadline posed challenges, the choice of Rust greatly contributed to the robustness and speed of development. The combination of asynchronous programming, safety features, and a rich crate ecosystem provided the tools needed for rapid, reliable email flow validation in a security context.

For security researchers and developers facing similar challenges, mastering Rust’s async capabilities and relevant crates can be a game-changer, especially when time is of the essence.

References:

Winkel, H. (2021). "Leveraging Rust for Network Security Tools." Journal of Cybersecurity, 7(2), 45-60.
Rust-lang.org. (2023). "Async Programming in Rust." [Online] Available at: https://rust-lang.github.io/async-book/
Mailparse Documentation. (2022). "Parsing Email Headers in Rust." Available at: https://docs.rs/mailparse/

🛠️ QA Tip

Pro Tip: Use TempoMail USA for generating disposable test accounts.

DEV Community