IT Forensics · Linux

Detecting web shells on Linux-Servern – Forensically identifying malicious Server scripts

A web shell is a script planted by an attacker on a compromised web server which, via a standard web request, enables arbitrary commands to be executed on the Server, thereby establishing persistent remote access.

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Web shells are often deliberately designed to blend in visually with existing, legitimate application files, which is why detecting them requires a thorough understanding of typical patterns and behaviours.

Why LanCologne?

Since its foundation, LanCologne has specialised in professional IT forensics. Our staff have decades of experience in the field of information technology and assist companies, solicitors, private individuals and, on a regular basis, the courts in the technical investigation of complex digital matters.

The examination is, as a matter of principle, carried out exclusively on a forensic copy, a forensic image or a data source captured in a technically equivalent manner that preserves the integrity of the evidence. The original evidence remains unchanged and is stored in a manner that preserves its integrity.

Our services

We systematically scan web server file systems for known and unknown web shell patterns, examine suspicious files in detail and reconstruct their usage history using existing logs.

Typical areas of application

Identification of web shells planted on compromised Servern devices
Reconstruction of the initial compromise vector
Evidence of commands executed via a web shell
Assessing the extent of the damage following the discovery of a web shell
Incident Response on Linux Systems
Judicial and non-judicial expert reports

This is how a web shell investigation is carried out

Once the system has been secured, the web server’s file system is systematically scanned for known web shell signatures and for suspicious script patterns with unusual structures. Any web shells found are analysed in detail, and their usage is reconstructed chronologically using web server logs.

Why is web shell detection relevant from a forensic perspective?

An undetected web shell allows an attacker persistent access to a system – access that is often difficult to detect – which is why thoroughly identifying such shells is a key prerequisite for a complete clean-up.

Analysing the commands actually executed via a web shell also provides important insights into the true scale of an incident, for example with regard to a potential data breach.

Frequently Asked Questions

How are web shells typically detected?+
Through a combination of signature-based detection of known patterns and manual analysis of structurally unusual, obfuscated script files.
How does a web shell get onto a Server?+
Often via an exploited vulnerability in a web application, such as an insecure file upload function.
Is it possible to fully reconstruct the use of a web shell retrospectively?+
Depending on the available records, it is possible to reconstruct events to a large extent, although not always without gaps.

LanCologne – Linux Forensics Cologne

Do you require a professional forensic investigation into „Detecting web shells on Linux-Servern"? LanCologne can assist you with the legally admissible preservation of digital evidence and the transparent analysis of relevant Linux artefacts.

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