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System Files Typical File Size Detection with YARA

YARA Rules to Detect Uncommon System File Sizes

YARA is an awesome tool especially for incident responders and forensic investigators. In my scanners I use YARA for anomaly detection on files. I already created some articles on „Detecting System File Anomalies with YARA“ which focus on the expected contents of system files but today I would like to focus on the size of […]

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Endpoint Attacker Detection

Synergetic Effects of Network and Host Based APT Detection

People often ask me if they still need our host based scanner THOR now that they have bought a network appliance that already checks all content that goes into and leaves their network. I normally answer that it is not a question of one solution versus another, but a combination of solutions to achieve the […]

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APT Detection is About Metadata

People often ask me, why we changed the name of our scanner from „IOC“ to „APT“ scanner and if we did that only for marketing reasons. But don’t worry, this blog post is just as little a sales pitch as it is an attempt to create a new product class. I’ll show you why APT […]

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Yara signature definition

How to Write Simple but Sound Yara Rules

During the last 2 years I wrote approximately 2000 Yara rules based on samples found during our incident response investigations. A lot of security professionals noticed that Yara provides an easy and effective way to write custom rules based on strings or byte sequences found in their samples and allows them as end user to […]

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Signature Matching sethc.exe

Inverse Yara Signature Matching (Part 1/2)

During our investigations we encountered situations in which attackers replaced valid system files with other system files to achieve persistence and establish a backdoor on the systems. The most frequently used method was the replacement of the „sethc.exe“ with the valid command line „cmd.exe“ to establish a backdoor right in logon screen by pressing shift […]

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