Filesec.io
Tool Description: A reference database of file extensions commonly associated with executable, scripting, phishing, macro, and other potentially risky behaviours.
Filesec.io
Quick Overview
What it does
Catalogues file extensions, their functions, operating systems, and potential security risks.
How to use it
Search for a file extension, function or operating system, then review the associated classification.
Cost
Free.
Account required
No.
Cookies
Primarily functional/security cookies.
Ownership
The site is associated with security researcher mrd0x; its theme credits reference GTFOBins and LOLBAS.
Use in Reporting
Helps investigators explain why a file type may be suspicious, identify potentially dangerous extensions and support analysis of phishing/malware-related files.
What does Filesec.io do?
Filesec.io is an encyclopedia of potentially malicious or abuse-prone file extensions. The current site allows users to search by file extension, function, or operating system.
The database classifies extensions using categories including Executable, Script, Phishing, Double Click, Macros and File Archiver.
The lowdown: It’s described as a central resource for malicious file extensions, risks, operating systems and mitigations.
How to Use:
1. Identify the file extension you want to investigate, for example .lnk, .iso, .docm, .hta or .ps1 then search for the extension on the site or search by function/operating system using the site's search syntax.
You can also use filters such as ‘script’ and ‘phishing’ to pull up results for commonly used extensions:
2. Record the extension's classifications and use the information as context when analysing the actual file, campaign or incident. Where possible, corroborate the assessment with malware-analysis or threat-intelligence sources.
Cost
Data Processing
Account Required:
Cookies:
Filesec.io uses Laravel application cookies, including laravel_session and XSRF-TOKEN. laravel_session maintains the user's application session, while XSRF-TOKEN provides protection against Cross-Site Request Forgery (CSRF) attacks. These are primarily functional and security cookies rather than advertising or analytics cookies.
Use in Reporting
Filesec.io can be used to:
Identify potentially risky or security-relevant file extensions.
Determine whether a file extension is associated with executable, scripting, phishing or macro functionality.
Assess the potential significance of unfamiliar file types encountered during an investigation.
Support analysis of suspicious email attachments, downloaded files or files associated with phishing campaigns.
Compare file-extension characteristics across different operating systems.
Provide context when explaining potentially malicious file types in an investigative report.
Support technical findings alongside malware-analysis, sandboxing and other independent sources.
Capabilities
Limitations
Large catalogue of file extensions associated with security-relevant behaviour.
It does not analyse or sandbox the actual file submitted by an investigator.
Searchable by extension, function and operating system.
Classifications provide context rather than a complete threat assessment.
Classifies extensions into categories such as executable, script, phishing and macros.
It does not replace antivirus, sandboxing, reverse engineering or malware-analysis tools.
Useful for identifying potentially risky or unusual file types.
Information may not capture every new or emerging abuse technique immediately.
Covers Windows, macOS and Linux file types.
A file extension alone does not establish that a file is malicious.
Useful as a quick reference during cyber/OSINT investigations.
Some classifications are broad and require technical interpretation and corroboration.
Summary
Filesec.io is particularly useful during initial triage when an investigator encounters an unfamiliar or suspicious file extension and needs to understand its potential significance before conducting deeper analysis.
Note: It should be treated as a reference source rather than a malware-detection service.
Ownership
Filesec.io is associated with the security researcher mrd0x.
Ethical Considerations
Use Filesec.io to understand and investigate potentially malicious files rather than to facilitate malicious file delivery.
Do not execute suspicious files on a normal workstation simply because their extension appears in the database.
Treat file-extension classifications as indicators, not proof of maliciousness.
Do not download or open suspicious samples unnecessarily.
When reporting findings, distinguish between the file extension and the actual behaviour of the file.
Corroborate important conclusions with malware-analysis, sandboxing, vendor research or other authoritative sources.
Related Tools:
LOLBAS
GTFOBins
MalwareBazaar
Sources
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