Step-by-Step Incident Response

When a critical enterprise server is breached, a well thought-out incident response plan will help you contain damage, speed up service restoration, and collect forensic information. If you have reason to believe that a system has been compromised, either by an Intrusion Detection alert or by suspicious activity, the first thing to do is isolate the system before it can do damage. It is most likely dangerous to log into the system and try to do a normal shutdown—the shutdown procedure could have been booby-trapped to cause the system to self-destruct. Likewise, rebooting the system is risky – again, a booby trap could have been inserted. Even logging into the system is unsafe, as trusted programs could have been replaced with malicious Trojans. In fact, a compromised system is never what it seems—a skilled attacker will hide his malware and create the illusion that all is as it should be, when the reality is that the machine is actually a zombie. A compromised machine cannot be trusted at all…

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File timestamps are used by forensics practitioners as a fundamental artifact. For example, the creation of user files can show traces of user activity, while system files, like configuration and log files, typically reveal when a program was run. 

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In this paper, we review how each layer of the software stack (kernel, file system, libraries, application) influences MACB timestamps on Unix systems such as Linux, OpenBSD, FreeBSD and macOS.

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Our implementation covers four different operating systems, the GIO and Qt library, as well as several user mode applications and is released as open-source.

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Furthermore, we provide tables summarizing timestamp behavior aimed to be used by practitioners as a quick-reference.

Learn more: https://dfrws.org/presentation/a-systematic-approach-to-understanding-macb-timestamps-on-unixlike-systems/

File timestamps are used by forensics practitioners as a fundamental artifact. For example, the creation of user files can show traces of user activity, while system files, like configuration and log files, typically reveal when a program was run.

Despite timestamps being ubiquitous, the understanding of their exact meaning is mostly overlooked in favor of fully-automated, correlation-based approaches. Existing work for practitioners aims at understanding Windows and is not directly applicable to Unix-like systems.

In this paper, we review how each layer of the software stack (kernel, file system, libraries, application) influences MACB timestamps on Unix systems such as Linux, OpenBSD, FreeBSD and macOS.

We examine how POSIX specifies the timestamp behavior and propose a framework for automatically profiling OS kernels, user mode libraries and applications, including compliance checks against POSIX.

Our implementation covers four different operating systems, the GIO and Qt library, as well as several user mode applications and is released as open-source.

Based on 187 compliance tests and automated profiling covering common file operations, we found multiple unexpected and non-compliant behaviors, both on common operations and in edge cases.

Furthermore, we provide tables summarizing timestamp behavior aimed to be used by practitioners as a quick-reference.

Learn more: https://dfrws.org/presentation/a-systematic-approach-to-understanding-macb-timestamps-on-unixlike-systems/

YouTube Video UCQajlJPesqmyWJDN52AZI4Q_i0zd7HtluzY

A Systematic Approach to Understanding MACB Timestamps on Unixlike Systems

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