What to expect when you’ve been hit with Avaddon ransomware

Avaddon ransomware is a Ransomware-as-a-Service (RaaS) that combines encryption with data theft and extortion. Avaddon has been around since 2019 but has become more prominent and aggressive since June 2020. “Affiliates” or customers of the service have been observed deploying Avaddon to a wide range of targets in multiple countries, often through malicious spam and phishing campaigns that carry booby-trapped JavaScript files.

Organizations hit with Avaddon ransomware face more than just data encryption – there is also the threat of public data exposure on the Avaddon leak site and, more recently, the risk of distributed denial of service (DDoS) attacks disrupting operations. These tactics are designed to increase pressure on victims to the ransom demanded.

The following information may help IT admins facing the impact of an attack with Avaddon ransomware.

According to reports appearing from May 17, 2021, the operators behind Avaddon ransomware have taken the service ‘”private” –  possibly by being more selective about affiliates and their targets – and have said they will not support attacks on sectors such as government, healthcare, educational, and charity organizations.

Editor’s note: This is part of a new series of “What to expect” guides featuring prevalent ransomware families. There is another guide available that covers Conti ransomware.

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What to do immediately: contain and neutralize

The first thing you need to do is determine whether the attack is still underway. If you suspect it is, and you don’t have the tools in place to stop it, determine which devices have been impacted and isolate them immediately. The easiest option is to simply unplug the network cable or turn off the Wi-Fi adapter. If the damage is more widespread than a few devices, consider doing this at the switch level and taking entire network segments offline instead of individual devices. Only shut down devices if you can’t disconnect the network.

Second, you need to assess the damage. Which endpoints, servers and operating systems were affected, what has been lost? Are your backups still intact or has the attacker deleted them? If they are intact, make an offline copy immediately. Also, which machines were protected? They’ll be critical in getting you back on your feet.

Third, do you have a comprehensive incident response plan in place? If not, you need to identify who should be involved in dealing with this incident. IT admins and senior management will be required, but you may also need to bring in outside security experts, consult with cyber insurance and legal counsel. Should you report the incident to law enforcement and/or inform data protection authorities? There is also the question of what information should be given to users and customers, many of whom are likely to arrive at work to face a similar ransom note on their desktop.

Last, but definitely not least: you’ll want to talk to people about what’s happening, but the attackers may be eavesdropping, so don’t use your normal channels of communication. If the intruders have been in your network for a while, they’ll probably have access to email, for instance.

What to do next: investigate

Once you have managed to contain and neutralize the attack, take time to investigate what happened so you can reduce the likelihood of it happening again. If you don’t feel confident about doing this yourself, there is specialist incident response and threat hunting help available 24/7 from security vendors, including Sophos.

According to the Sophos Rapid Response team, this is what you need to expect from Avaddon ransomware activity on your network:

1. The attackers have most likely been on your network for a few days or even weeks. Avaddon is a Ransomware-as-a-Service that includes data exfiltration. It is operated by human affiliates who earn a share of any ransom profits. The affiliates take time to explore a target’s network in order to find and steal high value data and ensure maximum disruption because this enables them to charge higher ransoms.

Sophos incident responders have seen intruder dwell times ranging from around 10 to 28 days in attacks that involved the release of Avaddon ransomware.

2. The attackers could use a variety of different methods to break in your network. Known initial access methods for Avaddon ransomware include, but are not limited to spam campaigns delivering malicious JavaScript files, exposed RDP (Remote Desktop Protocol) services and vulnerable virtual private networks (VPNs.) Sites like Shodan.io provide insight into what an attacker could find out about your network; try using it to search your external IP addresses.

Avaddon attackers target both Windows and Linux systems.

3. They will have secured access to domain admin accounts, as well as other user accounts. Attackers typically compromise multiple accounts during an attack. Their main goal is to get access to domain admin accounts they can use to launch the ransomware. However, they also target specific admin accounts that have access to sensitive data, backup systems, and security management consoles.

Avaddon attackers use tools like Mimikatz to steal account access credentials and for privilege escalation once they’re inside the network. Mimikatz can capture information from a running Microsoft LSASS.exe process that contains usernames/password hashes of currently logged on users. Sometimes attackers will leave this running and then deliberately break something on the machine that they’ve targeted, provoking an admin to log in to fix it. Attackers can then capture this admin’s credentials.

If Mimikatz is blocked by security software, the attackers may instead use something like Microsoft Process Monitor to do a memory dump of LSASS.exe and take that dump file back to their machine to extract the information with Mimikatz. With Mimikatz, it doesn’t matter how long or complex the passwords are because it is takes them straight out of memory.

4. They will have scanned your network. They know how many servers and endpoints you have and where you keep your backups, business-critical data and applications. One of the first things attackers do when they get onto a network is identify what access they have on the local machine. The next step is to find out what remote machines exist and if they can access them.

Avaddon ransomware operators, like many other hands-on-keyboard attackers, use RDP for internal lateral movement inside the network, using this to make their way onto servers and computers that carry high value assets.

5. The attackers are likely to have downloaded and installed backdoors that allow them to come and go on your network and install additional tools. They’ll have set up folders and directories to collect and store stolen information and channels for communicating with the attackers and for moving information out of your network.

The backdoors come in a variety of forms. Some just communicate back to the attackers’ IP address, allowing them to send and receive commands to the machine.

Many backdoors are classified as legitimate applications. For example, the attackers might use Remote Administration tools such as RDP to maintain access. Even if RDP is disabled by default, it is very easy for an attacker with admin access to the machine to re-enable it. Another common legitimate tool used is AnyDesk. This offers attackers direct control of the machine, including control over the mouse/keyboard and the ability to see the screen.

Avaddon operators are known to use Cobalt Strike, an advanced post-exploitation pen-testing tool. Attackers will often try and establish a Cobalt Strike “beacon.” This allows regular communication back to the Cobalt Strike server (the “command-and-control” for the Avaddon attack) and gives attackers complete control of the machine. It can also be used to easily deploy further beacons on other machines inside the network.

6. In addition to the encryption of data and disruption to software and operations, Avaddon operators will try to exfiltrate corporate data prior to the main ransomware event. Incident responders who investigated attacks involving Avaddon found that the operators had used the archive tool WinRar to collect data for exfiltration and then exfiltrated the data to the www.Mega.nz cloud storage provider, using their MegaSync application. Mega is popular with adversaries because it offers them a level of anonymity.

7. They will have tried to encrypt, delete, reset, or uninstall your backups. Unless your backups are stored offline, they are within reach of the attackers. A “backup” that is online and available all the time is just a second copy of the files waiting to be encrypted.

8. The attackers will have tried to identify what security solution is used on the network and whether they can disable it. It doesn’t matter how good your protection is if the attacker can turn it off.

Free default tools, such as Windows Defender, can be disabled instantly by anyone with enough admin rights. Most modern ransomware attempts to do this by default. Attackers also try to find and gain access to the management consoles of more advanced security solutions in order to disable all protection just before they launch the ransomware.

Security management consoles hosted locally are especially at risk as attackers could access them with the accounts they have already compromised.

9. The most visible part of the attack – the release of ransomware – probably took place when no IT admins or security professionals were online to notice and prevent the lengthy process of file encryption, possibly during the middle of the night or during the weekend.

NoteThe encryption process takes hours. An encrypted Windows endpoint will have tens or hundreds of thousands of encrypted files by the time the ransomware is done. For large file servers this could run into the millions. This is why most targeted ransomware attacks are launched in the middle of the night, over a weekend or on a holiday, when fewer people are watching.

Up to this point, the attackers have been trying to stay hidden, but here their tactics change. They want you to know they are there and what they have done. They want you to see how much data has been lost and to understand that someone has done this maliciously and now they want a payment to decrypt the data.

This is why, in almost all ransomware attacks, encrypted files will have had a new extension name appended to the end of the file. For example, “MyReport.docx” might become “MyReport.docx.encrypted.” The ransom notes are often displayed prominently in multiple places, adding to the chaos and stress.

10. The ransomware will have been deployed to all your endpoints and any servers that were online at the time of attack – providing that is what the attacker wanted. Ransomware is “deployed” like a normal application; in most attacks it doesn’t spread randomly in all directions. If your servers were encrypted, but not your endpoints, that is because the attacker chose to only target your servers.

The ransomware can be deployed in a variety of ways. In the case of Avaddon, the attackers are likely to have created a scheduled tasks on endpoints and servers across the network that deployed the ransomware at a pre-defined time.

Another method, commonly used by many different ransomware families is a combination of batch scripts and the Microsoft PsExec tool, which is a great tool for executing commands on remote machines. An attacker might create a batch script that loops through a list of your IP addresses, using PsExec to copy the ransomware to each machine and then execute it.

While most security solutions (including Sophos’) block PsExec by default, admins often authorize its use on their network because they find it useful too – and unfortunately the attackers know this.

Attackers could also create or edit an existing Group Policy Object (GPO) logon script. If you fail to spot this, the attack could relaunch every time a machine boots up and connects to the domain. This makes it seem like the ransomware is “spreading” when it is just caused by the GPO.

11. The launch of the ransomware is not the end. The Avaddon attackers may use the tools they installed earlier to remain in the network to monitor the situation and even your email communications to see how you respond to the release of the ransomware. An email to the CEO stating you will be OK because they didn’t encrypt the backups on Server X, could be a disaster if the attacker read it and still had access to that server.

The attacker may also wait until you recover to then launch a second attack to really emphasize that they can keep doing this until you pay.

Avaddon attackers have another tactic designed to pressurize targets into paying: they launch a DDoS attack in an attempt to disrupt operations and communications.

12. The time spent in your network will likely have allowed the attackers to steal business critical, sensitive and confidential information that they now threaten to publicly expose. The Avaddon RaaS controllers operate a public “leak site”: avaddongun7rngel[.]onion. Targets hit by Avaddon affiliates are threatened with the risk of their data being published on the site for anyone to view, unless they pay the ransom. Some of the more valuable data could be sold to other attackers to use in further attacks.

Avaddon attackers claim they will start publishing stolen data anywhere from a few days to a week after the main attack if no contact from the target is received or negotiations break down. They normally begin by releasing about 5% of the data they claim to hold. However, it could be several weeks or even longer before anything gets published.

Further, while the attackers may promise to delete your information if you pay, you have no guarantees that they will.

What defenders can do

There are some proactive steps you can take to enhance your IT security for the future, including:

  • Monitor your network security 24/7 and be aware of the five early indicators an attacker is present to stop ransomware attacks before they launch
  • Shut down internet-facing remote desktop protocol (RDP) to deny cybercriminals access to networks. If you need access to RDP, put it behind a VPN connection and enforce the use of Multi-Factor Authentication (MFA)
  • Educate employees on what to look out for in terms of phishing and malicious spam and introduce robust security policies
  • Keep regular backups of your most important and current data on an offline storage device. The standard recommendation for backups is to follow the 3-2-1 method: 3 copies of the data, using 2 different systems, 1 of which is offline
  • Prevent attackers from getting access to and disabling your security: choose an advanced solution with a cloud-hosted management console with multi-factor authentication enabled and Role Based Administration to limit access rights
  • Remember, there is no single silver bullet for protection, and a layered, defence-in-depth security model is essential – extend it to all endpoints and servers and ensure they can share security-related data
  • Have an effective incident response plan in place and update it as needed. If you don’t feel confident you have the skills or resources in place to do this, to monitor threats or to respond to emergency incidents, consider turning to external experts for help.


Dealing with a cyberattack is a stressful experience. It can be tempting to clear the immediate threat and close the book on the incident, but the truth is that in doing so you are unlikely to have eliminated all traces of the attack. It is important that you take time to identify how the attackers got in, learn from any mistakes and make improvements to your security. If you don’t, you run the risk that the same attacker or another one might come and do this to you again next week.

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