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How to Write Simple but Sound Yara Rules – Part 3

It has been a while since I wrote „How to Write Simple but Sound Yara Rules – Part 2„. Since then I changed my rule creation method to generate more versatile rules that can also be used for in-memory detection. Furthermore new features were added to yarGen and yarAnalyzer. Binarly The most important feature of […]

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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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Yara Signatures

How to Write Simple but Sound Yara Rules – Part 2

Months ago I wrote a blog article on „How to write simple but sound Yara rules„. Since then the mentioned techniques and tools have improved. I’d like to give you a brief update on certain Yara features that I frequently use and tools that I use to generate and test my rules. (mehr …)

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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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Yara Anomaly Scanner

How to Scan for System File Manipulations with Yara (Part 2/2)

As a follow up on my first article about inverse matching yara rules I would like to add a tutorial on how to scan for system file manipulations using Yara and Powershell. The idea of inverse matching is that we do not scan for something malicious that we already know but for anomalies within the […]

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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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Howto detect Ebury SSH Backdoor

Die folgende Yara Signatur kann für die Erkennung der Ebury SSH Backdoor verwendet werden. rule Ebury_SSHD_Malware_Linux { meta: description = "Ebury Malware" author = "Florian Roth" hash = "4a332ea231df95ba813a5914660979a2" strings: $s0 = "keyctl_set_reqkey_keyring" fullword $s1 = "recursive_session_key_scan" fullword $s2 = "keyctl_session_to_parent" fullword $s3 = "keyctl_assume_authority" fullword $s4 = "keyctl_get_security_alloc" fullword $s5 = "keyctl_instantiate_iov" fullword $s6 […]

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