<img height="1" width="1" style="display:none" src="https://www.facebook.com/tr?id=116645602292181&amp;ev=PageView&amp;noscript=1">

Subscribe for Updates

 

In August, we hosted our first ever Cybereason Capture The Flag competition. While we intended to start small and grow, we had an impressive level of participation approaching almost 900 people! We had a blast building the challenges and interacting with all the participants, and hope you’ll join us for a future event!

We heard your feedback: More, More, MORE! We are working on the next iteration, so stay tuned for our next CTF announcement. Until then, here are some notes on the summer challenges to hold you over: 

Challenge Overview

BASIC | Executive Retreat to Amity Island

This was an enumeration JS script challenge. A web page of the Cybereason executive management team was provided. Clicking on each name provided a bio. As nearly all of the participants observed, our Chief Executive Officer was missing from the page. Modifying the ID=URL parameter to id=1 would provide his bio and the flag. 

Malop

In this challenge, we asked participants to find the hash of a file that was used in a phishing attack. All that was provided was a machine name and login to the Cybereason Defense Platform. There were two ways to solve it using the provided Cybereason EDR instance.

Strategy One: Browse to Malops, where you investigate malicious operations, and select the phishing Malop. Scroll to the process section, and click investigate to see the Excel process details, along with the file that was opened.

Strategy Two: From Investigations, construct a query with the following logic: 

Machine (Filter for Machine name) --> Process (Filtered for phishing suspicion) -> Files

Been There

This required using a dictionary brute force attack to find a password. A LSASS dump was provided. The intended path to the flag was to use Mimikatz to dump the LM Hash. Once you have the hash, crack the password using Hashcat and the best64 rule set. 

Turns out, our google fu wasn’t fu -- some hash sites had the precomputed hash that you could search to find the password. Completely valid method, although this wasn’t intended.

INTERMEDIATE | It's a shame really

In this network challenge, we provided a network service that could be connected to with telnet. When connected, a PIN prompt was displayed.

We recommend writing a script, such as in Python, to brute force the pin. This can be completed in a few lines in Python. Once a correct pin was entered (which was randomized on connection), a flag was output.

Swiftly

For this web log based challenge, we provided an hra file, a type of proxy or web transaction log. A vague description about RAID levels and the @SwiftOnSecurity Twitter account would lead you to find a transaction loading a tweet that implied, “Using RAID in place of a proper backup solution makes someone a clown.” (Their words, not ours).

And with some quick deduction, a flag of “clown” got points.

I'm Not Even Supposed to Be Here Today

In this analysis challenge, we asked participants to login to Cybereason and investigate a machine which we convicted earlier as being part of a phishing attack. The challenge was to identify the process that pulled down a command-and-control (C2) payload.

Product-Screen-A

This was a tricky question. The attack spawned a child process to pull down a payload for C2. This stealthy technique was much less obvious than the first two stages of the attack.

Most people got the answer once they slowed down and analyzed the entire process tree associated with the phishing attack. 

ADVANCED | Really, This Should be Easier

The second most talked about challenge! Participants needed to analyze a go lang binary in order to find the flag. 

There are two ways to solve this:

  1. Set breakpoints and dump the process memory when entering a password to get the flag
  2. Review the binary and find the two base64 strings that contained the flag. This is tricky as GO bins are messy at best, and the base64 is not easy to find in a strings dump.

“””

package main

import "fmt"

import "strings"

import "os"

import "bufio"

import b64 "encoding/base64"

func Password_Cat() string {

    var flag string

    flag = "Cyber"

    flag = flag + "eason"

    flag = flag + " Summer"

    flag = flag + "X.X"

    flag = flag + " CTF2020&01"

    flag = strings.Replace(flag,"X.X","",-1)

    flag = strings.Replace(flag, "2020", "", -1)

    return flag

}

func Flag_cat() string {

    var password string

    password = "SWYgeW91IGNyYWNrZWQgdGhpcw=="

    passwordDec, _  := b64.StdEncoding.DecodeString(password)

    password = string(passwordDec)

    passwordDec, _ = b64.StdEncoding.DecodeString("eW91IGFyZSBhIGdvb2QgcmV2ZXJzZXI=")

    passwordDec2 := string(passwordDec)

    password = password+" "+passwordDec2

    password = b64.StdEncoding.EncodeToString([]byte(password))

    return password

}

func main() {

    fmt.Print("Enter Password: ")

    user_input,_,err := bufio.NewReader(os.Stdin).ReadLine();

    if err != nil {

        fmt.Println("No input Detected")

    }

    if string(user_input) == Password_Cat() {

        flag, _ := b64.StdEncoding.DecodeString(Flag_cat())

        fmt.Println("Flag: "+string(flag))

    } else {

        fmt.Println("Well, that didn't work. Try Again")

    }

}

“””””””


Are You Still Investigating That?

At this point, participants used Cybereason EDR to investigate the phishing attack. We asked participants to find the mobile device that connected to the same C2 server in the earlier CR challenge. 

A query using our investigation screen allowed us to get this answer quickly. Filter for device type of Android or iOS, select the network relationship node, and filter for connections with a DNS query containing the C2 server.

Images != Password Vaults

The most discussed challenge! The solution is easy once you know it. This was a picture of a flag, with the picture metadata edited to have a smaller than actual pixel length in the header. The picture would display truncated.

There are a few ways to solve this challenge. 

  • Edit the header manually until you get the flag. 
  • A script could be used to modify the height and check the CRC if it was valid. Once valid you had a corrected image.

A Thin Pane of Glass

Finally, this was a Windows event log challenge.  A security event log from a Windows machine was provided. One account had a login with a login type of 10, which denotes a remote interactive login. We asked participants which account was used remotely. Finding this account name was the flag. As an option, you could brute force or try all of the account names, but what’s the fun in that!

Capture the flag events are a highlight of working in the security industry. It’s a fun way to learn from each other, develop new skills, and make new friends along the way. We have been ecstatic to be able to join this part of the community, bring defenders together, and create a forum for learning. We will continue these, and similar types of events  moving forward.  Of course, if you have feedback please reach out. Being part of the community means listening to you! 

Be sure to sign up to receive updates on our Winter CTF coming in February!