Category: Strategy

Log4Shell Defense

Log4Shell exploitation and hunting on VMware Horizon (CVE-2021-44228)


Go and run this on the connection servers:

It’s crude so also look for the modified timestamps, recent unexpected blast service restarts and if you have process logging go and check for suspicious child processes over the period. Once you have checked, run a backup, then if they aren’t patched, patch the servers! (i know patching isn’t as simple as just patch!)


In Decemebr a critical vulnerability (created by a feature request) in Log4J was discovered (named Log4Shell), unveiling the reality that an enormous amount of products may be vulnrable to a relativley simple remote code execution vulnerability (which includs a huge range of internet facing systems, such as vmware horizon).

I’m going to be vaugue here on purpose, mainly because I’m not omnipotent and the scale of the challenge here is significnatly large that it’s subject to change. The constant phrase with log4shell is “dynamic and evolving”. To be blunt, the intel we are getting is changing very rapdily from both a threat and vulnerability perspective.

The Log4J scenario to some is a non event, but when we look at this at scale and when we look at certainly technology stacks it has really serious poential for negative impact. Public facing services such as:

  • VMware Horizon
  • VMware Vcenter (don’t ask why people put this online but it seems lots them do!)
  • VMware Worksapce One
  • Mobile Iron
  • Unifi
  • Citrix XenMobile
  • Fidelis commandpost

For a list of currently known affected products please see:

Vmware Horizon World View

As you can see there are potentially one or two horizon services exposed! (let alone vcenters)


Eraly December ~9th Decemeber 2021 the vulnerability was publically disclosed

12/12/2021 – Vmware publishes KB to partially address the vulnerability (workaround) on vmware horizon ( – this has been updated all through December

12/12/2021 – VMware publishes advisory

13/12/2021 – UK NCSC Advisory

16/12/2021 – VMWare Horizon “Fixed” Builds released

17/12/2021 – VMware Horizon releases new builds for some version of Horizon

23/12/2021 – Exploitation of VMware Horizon discovered in the wild (across geos from the CTI we have)

24/12/2021 Active in the wild exploitaiton of vmware horizon

25/12/2021 – Active in the wild exploitation of vmware horizon

03/01/2022 – Microsoft Update

05/01/2022 – mRr3b00t publishes initial backdoor detection script in Github (

05/01/2022 – NHSD Publishes

07/01/222 – PwnDefend Post with detection examples

14/01/2022 – Increased detection activity noted (


The Log4J Payloads into the web services aren’t so easy to detect. They will basically look like standard traffic and without full packet captures and TLS inspection you almost certainly (based on research in the lab) see the malicious payloads.

You will in the logs however see error events, so there will be a ton of logs in the UAGs and Connection server logs that occur when a failed attempt to exploit log4j occurs.

In short (but subject to loads of configuration and environmental variance) we have found:

In the standard vmware logs you will largely not see exploitation. You will likely see failed exploitaiton attempts. There are some logs which show a connection but the metadata is limited. E.g. it will hav source IP, time and path however depending upon your load balancer configurations you may just see the UAG connect to the Connection server and access a path used in normal operations.

Process Logging

Process logging in sysmon will show excution of both log4j when the java child processes are spawned. It however possible that a malicious class load could run in memory and use native win32 APIs and NOT spawn a child process (we haven’t tested that yet).


Backdoors can be detected by looking for file modifications here: (default path) C:\Program Files\VMware\VMware View\Server\appblastgateway\lib

The script I knocked up is crude but will detect the activity seen recently in the wild.

you can also use a PowerShell one liner:

$path=gwmi win32_service|?{$_.Name -like "*VMBlastSG*"}|%{$_.PathName -replace "nssm.exe","lib\absg-worker.js"};$path = $path -replace'"',''  ;Get-Content $path|Select-String "req.headers\[\'data\'\]"

you can also look at the modification stamps:

$path=gwmi win32_service|?{$_.Name -like "*VMBlastSG*"}|%{$_.PathName -replace "nssm.exe","lib\"};$path = $path -replace'"',''  ;dir $path

In our testing we have found the stamps on all files should be the same, a file with a different date has likely been modified in a suspicious manner.

Microsoft Defender for Endpoint

These queries can be narrowed down and you should filter these onto your specific Horizon infrastrcuture, so they are examples for guidance, you will likely need to do some tweaks and mods:

Log4J (TCP 443) child process creations (check for benign normal child processes)

Look for evil using powershell etc.

| where DeviceName has_any("horizon-con-001") //connection server name
| where InitiatingProcessParentFileName ==  @"ws_TomcatService.exe"
| order by Timestamp desc

Check for backdoors being created by powershell for file modification events:

| where FileName has_any("absg")
| where FolderPath has_any("appblastgateway")
| where ActionType == "FileModified"
| where InitiatingProcessCommandLine has_any("powershell")
| order by Timestamp desc 

Check network connections from ws_TomcatService.exe

| where DeviceName has_any("horizon-con-001")
| where InitiatingProcessCommandLine == @"""ws_TomcatService.exe"" -SCMStartup TomcatService"
| where RemoteIP != @""
| where ActionType == @"ConnectionSuccess"

Please note that in our lab testing we do not see all the connections in MDE. So this data is deemed to be incomplete:

Backdoor Usage (TCP 8443)

The backdoor seen is in absg-worker.js (but remember the log4j rce here could be used in many many ways:

You can see in this instance the modified date looking quite out of place against the files peers.

| where DeviceName has_any("horizon-con-001") //connection server name
| where InitiatingProcessParentFileName == @"node.exe"
| order by Timestamp desc

In our limited testing we can see backdoor usage whch spawns child processes from node.exe

We should also note both in the lab and in the wild we have seen the following:

A very simmilar message is logged on the connection server when a failed backdoor attempt is made. This can be found in:

C:\ProgramData\VMware\VDM\logs\Blast Secure Gateway\absg.log

Service Restart Events

If a backdoor is installed to the BLAST service then you will likely see the service restart at an unexpected time:

Get-EventLog -LogName "System" -Source "Service Control Manager" -EntryType "Information" -Message "*VMWARE*running*"

that will list all the service restarts in the SYSTEM log on the Connection Server/s or we can just grab the blast service:

Get-EventLog -LogName "System" -Source "Service Control Manager" -EntryType "Information" -Message "*Horizon View Blast Secure Gateway*running*"

Useful logs

  • If WAF is inline WAF logs would be useful
  • SYSMON (process launches, dns events)
  • EDR Process Logging (process launches, file writes)
  • Load Balancer HTTP Traffic Logs
  • Connection Server debug logs and blast logs
  • Firewall (ingress and egress traffic logs)
  • UAG blast logs
  • DNS Logs (however we are seeing threat actors use IP addresses for the LDAP call backs)

Vmware Horizon Log Levels

In the lab we observed the following:

  • By default the UAG log level was set to INFO
  • Debug logging is set on the connection server (assumed based on filename)

With INFO logging on the UAG we weren’t able to determine if a malicious payload had been sent. In the ESMANAGER log successful connections were not logged.

We could see the connection on the backend connection server however we could not determine this was a malicous payload in the default logging configuration.

in DEBUG mode we could see the connections and PALOADS on the UAG.

Exploitation Entry Points

There are at least two pages on the HTML Access services that are vulnerable when ther server are unpatched:

  • /broker/xml
  • /portal/info.jsp

Please note we’ve had mixed results with /brokes/xml which may be build version specific.

Threat Intel

Micosoft has reported DEV-0401 using Log4Shell in relation to ransomware activity:


This post will likely be updated, it’s not a step by step of how to find all the evil but it hopefully will help identify malcious activity seen in the real world. We will update this if new intel comes in.

Also if you want to wite nicer detections feel free 🙂 these are just examples and are by no means the only ways to do this!

Exploitation Tutorial

When people have had more time to patch and the landscape looks better we will blog how to exploit this and talk about why the currently known backdoor has some limitations due to the service architecture and how the backdoor has been created. It’s important to share exploitation knowledge but there are things to consider, if you are sharing exploitation without detection rules / tools this creates a risk to people. VMware products and services are leveraged by organisations worldwide and the log4j RCE on hoirzon let alone the backdoor can be leveraged for high impact actions by threat actors.


Thanks to everyone in the community and industry who has and is helping, thanks to all of those who have stayed up late, missed familty events and generally been super helpful either indirectly or directly. There are lots of people involved in this world who everyday work to keep people safe! (also to my friends and family who have put up with my not being round much!).


Post Business Email Compromise actions for Office 365 Users

If you have a business email compromise incident and you haven’t deteced it in a timely manner your fist notification might be a bad experiance, the threat actors may have commited fraud, attemped fraud or simply launched a phishing If you have a business email compromise incident and you haven’t detected it in a timely manner your fist notification might be a bad experience, the threat actors may have committed fraud, attempted fraud, or simply launched a phishing campaign from your environment. If you are in this position, there are some steps you can take from a technical point of view to limit impact and reduce risk of a re-occurrence. This blog is a high-level view at some of the tactical and longer-term activities you can conduct.

Read more “Post Business Email Compromise actions for Office 365 Users”

I’m the CEO, why should I care about Cyber…


First and foremost, I’m going to start by saying if I include any cliché quotes it’s probably in an ironic context or used to show how they aren’t practically useful. Why are we here? Well, based on the title, it’s because you are either a CEO/MD or you are in a leadership position and want to learn a little more about cyber security.

I’m sure you have read the news, I’m sure you have seen vendor adverts explaining something like:

  • Zero Trust
  • The Security Skills Gap
  • How phishing can be solved through security awareness training (pro tip: it can’t)

And I’m sure someone on your LinkedIn feed you have seen people exclaim all kinds of crazy things like:

  • TLS Weaknesses Lead to Ransomware
  • Security is Simple (it, I’m afraid, is not)
  • Managed Security Service Providers ensure security

Read more “I’m the CEO, why should I care about Cyber Security?”


Can Cyber Deception be used as a force for…

Scams, Disinformation & Supply Chain Compromise

Now this might come to a shock to some of you but I’m not actually (as my LinkedIn profile currently says) Tony Stark! I know, shocking but it’s true. Why I’m experimenting with this will hopefully be apparent after reading this post (although this isn’t an explanation specifically). What I’m looking at is how deception is used from a range of perspectives from marketing, cybercrime and how we can use deception in a positive way, to actively defend ourselves from the cyber criminals! Read more “Can Cyber Deception be used as a force for good?”


Cloud Security – 26 Foundational Security Practises and Capabilities…

That is quite the catchy title don’t you agree? Ok so that needs some work and when we think about cloud security, we need to realise that Computing as a Service isn’t a silver bullet.

One Cloud to Rule them all and in the darkness bind them

Ok so the cloud was promised as the saviour of IT and Cyber security but the promise vs the reality. Well, let’s be frank, they don’t really match up. But have no fear – secure cloud design is here (omg cringe)! Ok now we have that out of my system let’s look at some basic cloud security considerations to make when thinking about cloud services.


Ok so the world doesn’t work with a checklist however, if you are like me you will want to use lists and aides to jog the little grey cells into action. Let’s think about cloud services and security: Read more “Cloud Security – 26 Foundational Security Practises and Capabilities Checklist”


Cyber Security Design Review


To conduct a solution review we need to consider multiple perspectives. Cyber security can be described as (from the NCSC):

“Cyber security’s core function is to protect the devices we all use (smartphones, laptops, tablets and computers), and the services we access – both online and at work – from theft or damage. It’s also about preventing unauthorised access to the vast amounts of personal information we store on these devices, and online.”

Cyber Security is concerned with risks, threats, vulnerabilities, and controls. This really means the breadth and depth of cyber security is vastly wide and terribly deep. Read more “Cyber Security Design Review”


Risk management is easy! Isn’t it?

Information security theory and practises use a commonly understood and simple range of tools, methods, and practises to help organisations understand their risk portfolio and to enable them to make both strategic and tactical investment decisions….

Ok someone pinch me. this simply isn’t the reality I see on the ground. The theory is vast, complex and there are a multitude of good/best/insert phrase frameworks and tools that you can leverage to map, model, and communicate risks, vulnerabilities, controls, threats etc.

I’m not going to do a detailed analysis and comparison of different models here, but I am going to at least give people a view of some of the tools and frameworks that you can and may likely experience in the cyber security world. Read more “Risk management is easy! Isn’t it?”


Cyber Security Architecture

I remember (now it was a long time ago) when I worked in a support role and my dream job was being a technical architect, back in the warm and fuzzy days of no host-based firewalls, IPsec being something only MCPs knew about other than the networking team and when cybercrime was a shadow of how it is today.

It wasn’t until I had a few more notches under my belt when I realised that architecture in technology has different viewpoints, not only that but even the industry can’t agree on what things are or are not. That aside the reality is, is that architecture has different domains, specialisms, views, and viewpoints. I often find myself working across a whole range of areas, that is driven largely by specific customer requirements and scenarios (this is why I have a cool lab and lots of kit!)

When we consider a business technology system it has risk and by nature cyber security in that view. To think of this not being the case would be odd because ultimately “business” is the highest abstraction, and let’s think about what makes up a business: Read more “Cyber Security Architecture”


Measuring Cyber Defence Success

What does “good” cyber security look like? Sure, we can run a maturity assessment and see what good indicators are and we can create a baseline of our current state to establish where we are and what gaps we have (honestly in real terms this isn’t something to consider you should be doing this!) but how do we measure success in cyber security? Is every success an invisible outcome? Because one question that often comes to mind here is, just because we don’t see something, does that mean everything is ok? In the fast-paced world of cyber security, measuring success isn’t as easy as you would think. I’ll give an example of this, let’s say we don’t monitor, we get breached, but the threat actor just performs crypto mining (let’s say this is on premises) and we never really notice in the grand scheme of the world that our energy consumption costs have increased, if we didn’t know this had occurred, we might think our security is good. Read more “Measuring Cyber Defence Success”