Ransomware is the nightmare of most of system administrators and security officers. It’s an emerging threat and the trend unfortunately is upward: more and more companies are being hit by ransomware, from small shops to large corporations.
In a previous post we discussed on how to use your QRadar to detect ongoing ransomware infections. In this post we will be discussing how to investigate ransomware attacks using your SIEM.
You may be wondering, “why bothering if it’s too late?”. It is extremely important to understand the vectors exploited and the timeline of the attack so we can avoid future infections and even stop current ransomware attacks.
Here’s a list of items to check using your QRadar:
- Anti Virus logs: That seems the most obvious thing to check. We can try to identify if the antivirus detected the threat and which was the first computer affected (the “entry point”). We can also check if the users infected had turned their antivirus off or if the ransomware was not even detected by the antivirus (a potential zero-day).
- Network Traffic: The majority of the ransomware strains communicate to a Command & Control server for two main reasons: synchronize the malware data, and in some cases, exfiltrate sensitive data. You can use your QRadar to find if your machines are connecting to a new external IP. For example, if you had all your HR laptops infected, and in the same period you observe all the laptops connecting to a new specific IP, that’s most likely the command and control server. You can blacklist this IP in your firewalls and create custom rules on QRadar to alert in case new machines trying to connect to this IP.
- Windows Logs: The windows logs can provide a lot of useful information
- Network Connection Logs: You can try to identify the command and control server by the windows network logs. Those logs can also indicate an anomalous number of connections in a port. For example, the latest ransomware threats were exploiting a vulnerability in the SMB protocol, so if you see an unusual number of connections on port 139 or 445, that may indicate a ransomware proliferating into your network. If that’s the case, you can disable the vulnerable service or block the connections on the windows firewall.
- File Modification Logs: As discussed in this previous post an ongoing ransomware infection generates a lot of “file update” logs. If you detect an anomalous number of file update logs, that may indicate a ransomware threat.
- USB Logs: Most of the ransomware attacks spread through emails and webpages, but they can also be delivered through infected USB sticks. If you know the approximate time of the infection, you can check for USB logs, looking for inserted devices. If the source is a USB stick, contact the user and make sure other people do not do the same.
- Email Logs: Most of the ransomware strains use an email phishing campaign as entry point in a company. Check your email logs (example: Microsoft Exchange logs) for suspicious attachments sent to internal users. If you find the first person infected, you can find the sender and prevent other people of receiving similar emails and getting infected.
- HTTP Logs: Ransomware can also be distributed through malicious websites. If you have your HTTP proxy logs, check for unusual downloads or unusual websites. If you find the source of the ransomware it is easy to block the access and avoid that other users get infected.
Having a proper incident investigation will help you to reduce the impact of an ongoing ransomware attack and may help you to prevent future attacks.
How do you investigate your ransomware attacks? Share with us in the comments.