During the last four years, I was engaged on incident response teams for several large advanced persistent threat (APT) cases involving different German corporations. In this time, we have developed methods and tools to detect compromised systems, while also planning and performing remediation. During the course of these investigations, I noticed that certain circumstances supported the chance that a corporation would fall victim to advanced persistent threats. In this article I want to focus on favorable preconditions that nearly ensure a successful APT attack.
The recommendations in this article were discussed and extended with the help of red team leaders and fellow CERT team members. This is an article inspired by a book named “Anleitung zum Herzinfarkt” by Bernhard Ludwig. This book provides serious guidance on how to increase the risk of dying from heart attack in someone’s early years. I found that this principle of a ‚humorous reversed guide‘ could be useful to describe the typical pitfalls and mistakes that we regard as crucial for the development of advanced persistent threats with the aim to help organizations, which have not been hit by this type of attacks so far.
Don’t Create Network Segments
At first, strictly avoid placing systems in different network segments. Instead – keep it simple. Let standard Windows workstations, admin workstations, server systems, print servers, industrial control systems, backup servers, network management systems, monitoring servers, terminal servers, mobile management servers, development systems, IP cameras, house automation, and SIP telephones be in a single huge network in order to avoid firewalling issues.
That principle applies also to subsidiaries and affiliates. After the acquisition of other companies, don’t waste time asking them for compliance with your security policies. Save time and connect their network directly with your backbone! Make sure to allow any type of connection and create domain trusts as fast as possible to enable cross-domain resource access to your data center in Berlin from your user workstations in Brazil, as well as the call center in Bangladesh.
If you are required to create network zones for some reason, interconnect these zones with mutual Windows domain trust relationships. (see Titanic as an example)
In order to maintain an environment of mutual trust and respect, never monitor the gateways between segments for port scanning, network sweeps, or other types of suspicious network activity. Also, please do not commit the new business unit to provide technical support in cases of suspicious activity and incident response.
Don’t Limit Privileged Account Usage
You trust your administrator, don’t you? So, let administrators use their privileged accounts to surf the web and read email while they are connected via SSH and RDP to their domain controllers and Internet facing servers in DMZ networks. Do not use hardened and intensely monitored jump servers from special admin workstations to manage your most important server networks.
Don’t waste precious resources creating administrative roles. If someone needs to install a text editor on a server, add him to the Domain Administrators group and make sure that no one ever figures out why you did this.
Do not use Microsoft’s solution called LAPS to ensure that all computers have different, complex, local administrator passwords or Privileged Admin Workstations (PAW) to provide a dedicated operating system for sensitive tasks. This would give attackers an unnecessarily hard time finding highly privileged credentials and fewer opportunities to use them.
Don’t Collect and Analyze Useful Log Data in a Central Location
Attackers tend to make themselves familiar with the environment and therefore cause strange peaks in log volumes that could be easily detected by an over-attentive employee – so, don’t log security events. If you do log events for any reason, make sure that all of your systems keep their logs in a local log file and do not transmit them to a central SIEM system.
If you have to use a SIEM system, use Active Directory for authentication, so that attackers can find all the fine log data in a central place. If you have any problems on a server, such as with disk space due to the fact that you configured your golden image for Windows servers to use only 20GB of space on drive ‚C:‘, don’t hesitate to reduce the log file size to a minimum. That may cause the log to overwrite itself every 30 minutes, but hey, each line that is overwritten can help prevent successful detection.
On Linux systems configure your log file rotation to keep 7 days, not more. Your IT staff typically needs a couple of days investigate the system owner and have some meaningful discussion with your data protection officer.
If you have to comply with certain policies that require the collection of log data, you still can do a lot to make sure that breaches remain undetected for months. Here is our Top 10:
- Only log and report high amounts of failed logins, because attackers tend to use valid credentials after taking the first hop
- Disregard all antivirus events that have the status „deleted“ or „moved to quarantine“. They are gone, so they won’t trouble you.
- Do not collect the logs of client workstations to avoid detecting zero-day attacks. Detecting them would cause pressure to take action.
- Do not search for anomalies in your log files because hacker activities generate some very special or completely new log types. If you look for them you could find them – so again, don’t do that.
- Do only collect the log files at system level and disregard the logs of applications running higher up.
- Do not spend time understanding your organization’s structure, logging completeness, and logging behavior of your assets. It’s usually pretty complex and the less you know the better.
- Use the default logging configuration on your systems. Maybe you miss the most relevant event types, but if they really were relevant, wouldn’t they be in the default anyway?
- Monitor and report attacks on your Internet-facing firewall to tie up valuable resources with useless pie charts.
- Do not collect the logs of SysInternals Sysmon, AppLocker, Windows Defender, or Microsoft EMET. The protection provided from their use, especially when combined, is far too effective.
- Let the data protection officers and workers‘ council decide on what you’re allowed to log and analyze.
Use your Active Directory for All Types of Authentication
Centralization is good. It saves resources and simplifies user administration. Use Active Directory authentication for everything: the logins to your proxy servers, network devices, online certificate authorities, virtual machine consoles, administrative jump hosts, security monitoring servers, VPN servers, SIEM system, and last but not least – backup servers.
This ensures that attackers take over the complete infrastructure after compromising a single outdated member server that has domain admin logon sessions. Remediation becomes much more exciting when attackers have access to proxies, DNS servers, and mail gateways all at once!
Don’t Regard the Client Workstations as the First Line of Defense
Since corporate workstations operate deep in the internal network, which are well protected by several firewalls and proxy servers, consider them to be far outside of the danger zone. Don’t audit them as frequently as you do with DMZ servers. There are so many more clients than servers that it is certainly not efficient to scan them all. Also, random samples never give a valid result, so let’s just drop the whole thing.
Simplify administration of user workstations by granting standard users local administrative rights.
Also allow workstations to access the Internet directly on any service port. Don’t use a proxy server and do not monitor dropped connections on typical Trojan back connect ports. Developers and administrators are highly skilled professionals that tend to download and install suspicious software from the shadiest websites. Remember: You trust them and if they think that they need that (suspicious) software than of course they do. To increase the probability of such events, block Sourceforge, Github, and the whole category „Software Downloads“ on your Internet proxy server.
Don’t Mind Antivirus Alerts
As mentioned before, do not consider antivirus alerts that have the status „deleted“, „cleaned“, or „moved to quarantine“. A deeper analysis of these events could reveal a Trojan that had control of the system for weeks before the right signature returned a match on components of a hack tool set that attackers moved from server to server. Therefore, do only check for errors and unresolved operational issues.
Make sure that no one pays special attention to antivirus events that report „Hack Tools“, „Password Dumpers“, or „Scanners“. Tell everyone that this would cause too many false positives because system administrators need these tools to find their assets and regain access to them.
Also avoid rating antivirus events according to an evaluation method. That’s so bureaucratic.
To allow attackers the greatest possible leeway, create vast exclusion lists and don’t use special Antivirus functions like PUA scanning or application controls that block password dumpers from accessing the memory.
Handle Web Servers Like Other Server Types
Regard web servers like any other server type. Frequently patching the web server service is perfectly sufficient. Do not audit the applications running on that web server; if you have to due to corporate policies, do it once, print the report, and archive it.
Place the web servers behind reverse proxy servers and tell everyone that this will protect them. If you repeat that constantly everyone will believe it one day. Do not protect the web servers with costly Web Application Firewalls and don’t collect the logs of such a system for central attack detection and analysis.
Allow developers to access the management interfaces, like JMX or Tomcat Manager, from remote locations. Don’t log access to these applications and don’t ban source IPs on security violations. Tell everyone that each developer may access the servers anytime, from anywhere, to reduce operational risks.
If you have to run Apache or Tomcat on a server, choose Windows as the operating system. Do not use limited user accounts to run the web server services in order to maximize the impact of a successful attack. Last but not least: Avoid annoying security features like SELinux.
A Few Last Words
I know that it is hard to guarantee a successful APT attack and that all of these recommendations require a certain amount of stubbornness and resistance to advice; however, even if this advice does not guarantee falling victim to advanced persistent threats, chances increase exponentially the more of my advice you apply. Good luck – I’ll keep my fingers crossed.
If you have further ideas that you want to share, please comment on this article or contact me on Twitter @cyb3rops.
Many thanks to Stephan Kaiser for the idea, Julia Stolz and Jeff for major reviews and Matthias Kaiser (@matthias_kaiser), Daniel Sauder (@DanielX4v3r), Thomas Patzke (@blubbfiction), Claas Rettinghausen, Robert Haist (@SleuthKid), Alexander Döhne for their valuable feedback.