Trust, in file based security

Trust, it’s a fundamental concept in cybersecurity and plays a vital role in the decisions we make, particularly if a risk based approach is taken to decision making. However, we don’t often think about how the concept of trust influences our decisions. This blog post will explore what role trust plays, in file based security.

First, it’s important to note that trust is not a one size fits all concept and is unable to be applied equally across situations. For example, trust between family members must be thought of as a completely different concept to trust between networked computer endpoints.

The oxford dictionary defines trust as:

Noun: “Firm belief in the reliability, truth, or ability of someone or something”.
Verb: “Allow someone to have, use, or look after (someone or something of importance or value) with confidence”.1

Looking at the above definitions, neither truly describes the concept of trust, when applied to files. Let me propose a more suitable definition (taking some inspiration from the Noun above):

“Firm belief in the purpose, origin and expected behavior of a file or software package”.

Let me clarify this statement. In order to decide if you should ‘trust’ a file you must satisfy the following criteria:

1) Context – The file must exist to serve a particular purpose and be attributable to an application or function. Humans should ask, why does the file exist?
2) Predictability – The file must behave in a predictable and consistent way when executed or handled. Humans should ask, does the file behave in a manner that is expected, given its context?
3) Integrity – The file must provide assurance that it has not been modified or tampered with in an unauthorized manner. Humans should ask, does the file have integrity?

Fig 1. Three domains of file trust

Answering these questions for every file on an average operating system can prove to be a daunting task, one that would simply be unfeasible using manual processes. Ultimately, we must rely on frameworks which can assist in determining if ‘trust’ should be placed in a file, at scale.

Frameworks can take many forms, such as a threat intelligence feed, hashing algorithm or even a digital certificate validation mechanism. Regardless of their function, these frameworks must be robust, as we rely upon them to provide accurate information to inform our decisions.

Now you may be thinking, what if I don’t fully ‘trust’ (have a firm belief in the reliability, truth or ability) the framework I am using? Where possible you should aim to use more than one framework to provide multiple answers for the ‘context’, ‘predictability’ and ‘integrity’ of a file. Multiple answers provide opportunity to compare the results across frameworks to ensure truthful answers are provided.

Typically, vendors/operators attempt to answer these questions using one or more of the following methods:

1) Context:

  • Has the file been seen by a large amount of users?
  • Has the file been signed by a vendor?
  • Is the file located in the correct path?
  • Does the file have a description explaining it’s purpose?

2) Predictability:

  • When is the file invoked?
  • Does the file perform any unexpected behaviors when invoked? (loading interpreters, spawning/hooking processes etc)
  • Does the file request elevated permissions?
  • Does the file load into the expected process?
  • Does the file perform any system modifications? Drop files?
  • Does the file extension match its content?

3) Integrity:

  • Is the file digitally signed by a vendor?
  • Does the files hash value match a vendor provided hash value?
  • Has the file changed hash values since I have seen the file?
  • Does the files hash match a known good sample based on threat intelligence?

These methods are not an exhaustive list and barely scratch the surface, but hopefully provide a starting point for some ideas which can be used to determine if you should trust a file or not.

Airlock Application Whitelisting provides a robust solution enabling administrators to easily choose which files they should trust in an environment. Most importantly, Airlock incorporates multiple frameworks which are needed to quickly determine trust.



Airlock releases free document to test chained trust in EDR and Application Whitelisting solutions

Today Airlock Digital is releasing a free Microsoft Word document to test ‘Chained Trust’ in EDR and Application Whitelisting solutions. is where a product will trust a parent process (such as winword.exe) and automatically place trust in any spawned child processes.

Security products that are configured to use ‘Chained Trust’ may provide a reduced level of security.

This document contains Macro code, which attempts to drop either a .dll or .exe file in the documents working directory and execute it, allowing you to audit product configurations.

You can download the document here:
SHA256Sum: e39b1abff16db7a7f6d3b52e6d01d29dd423da0504358082acd1073e439c5723

Please let us know if you find this useful or have any feedback by contacting or @airlockdigital.

Proactively Detect and Prevent Petya Ransomware

The Petya ransomware outbreak represents an evolution in the sophistication of ransomware. Employing a number of different strategies for distribution and infection the Petya ransomware has impacted small and large organisations across the globe.

This outbreak is another reminder that signature based detection is not effective in todays threat landscape.

In this video you will see the execution of Petya on a victim endpoint and discover how application whitelisting with Airlock provides zero-day proactive protection against Peta and other ransomware variants.


Remember to click the Full Screen button on the video to get a better view of the product interface.

Whitelisting & the Ransomware Worm

Ransomware activity has been rising steadily over the past four years, providing a low cost and successful income stream for criminal organisations. Over the past weekend however, the game was changed with ‘WannaCry’.

Traditional ransomware typically ran on a single end user system, encrypting files that were accessible on local disks and sometimes mapped network shares. The reason WannaCry had such a significant impact is the ability to spread aggressively through network connected computers (be that locally or over the internet) using a recently discovered Microsoft Windows SMB vulnerability. This vulnerability was patched by Microsoft in March 2017.

Even though WannaCry represents a worrying evolution in Ransomware tactics, the software itself isn’t designed with stealth and security evasion in mind. Simply by creating / mutating a new piece of software, the ransomware initially went undetected by nearly all traditional security products. The likely strategy with WannaCry was to hit the world hard and fast, before traditional security technologies like Anti-Virus and Network Intrusion Prevention has time to catch up and write detection signatures. The reactive nature of traditional security technologies are highlighted by the sheer number of hosts infected during this incident.

The Australian Signals Directorate’s (ASD) Strategies to Mitigate Cyber Security Incidents places Application Whitelisting as the number one ‘essential’ strategy to prevent malware delivery and execution. During the execution of WannaCry, five executable files are dropped and executed on the victims system. With the installation process involving the downloading of ‘Tor’ software to facilitate payment. If these executable files were proactively prevented from running, the attack would simply fail.

Incidents such as WannaCry demonstrate the need for proactive security solutions that make it extremely difficult for attackers to run malicious code. Application Whitelisting represents the most effective and proactive strategy to detect and prevent these attacks.

David Cottingham presenting at ACSC2107

Airlock Co-Founder, David Cottingham, will be presenting at the Australian Cyber Security Centre on Wednesday the 15th of March at 2:30pm in the Bradman Theatrette.

Presentation Abstract:

There is a wealth of information in the security community today about what constitutes an indication of malicious activity within enterprise environments. Even if you are lucky enough to have a consensus regarding what you should be looking for each day, many organisations are simply not resourced to actively hunt and interpret activity within their environment. During this talk I will release a free Splunk application I have developed to make this challenge easier and also demonstrate some additional utilities I find invaluable.

Information on the new free Airlock Splunk App can be found here, and an updated version of the Airlock Whitelist Auditor can be found here.