Sigma rule: HTTP Request to Low Reputation TLD or Suspicious File Extension

Rule

Title

HTTP Request to Low Reputation TLD or Suspicious File Extension

Status

experimental

Level

medium

Author

@signalblur, Corelight

Date

2025-02-26

File

rules/network/zeek/zeek_http_susp_file_ext_from_susp_tld.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects HTTP requests to low reputation TLDs (e.g. .xyz, .top, .ru) or ending in suspicious file extensions (.exe, .dll, .hta), which may indicate malicious activity.

Log source

product

zeek

service

http

Detection

# Suspicious TLD in the 'host' field OR malicious file extension in the 'uri' field.
selection_suspicious_tld:
    host|endswith:
        - '.bid'
        - '.by'
        - '.cf'
        - '.click'
        - '.cm'
        - '.ga'
        - '.gq'
        - '.ir'
        - '.kp'
        - '.loan'
        - '.ml'
        - '.mm'
        - '.party'
        - '.pw'
        - '.ru'
        - '.su'
        - '.sy'
        - '.tk'
        - '.top'
        - '.tv'
        - '.ve'
        - '.work'
        - '.xyz'
selection_malicious_ext:
    uri|endswith:
        - '.bat'
        - '.bin'
        - '.cmd'
        - '.cpl'
        - '.dll'
        - '.dylib'
        - '.elf'
        - '.exe'
        - '.hta'
        - '.iso'
        - '.jar'
        - '.js'
        - '.lnk'
        - '.msi'
        - '.pif'
        - '.ps1'
        - '.py'
        - '.reg'
        - '.scr'
        - '.sh'
        - '.so'
        - '.vbs'
        - '.wsf'
selection_malicious_mime:
    resp_mime_types:
        - 'application/vnd.microsoft.portable-executable'
        - 'application/x-bat'
        - 'application/x-dosexec'
        - 'application/x-elf'
        - 'application/x-iso9660-image'
        - 'application/x-java-archive'
        - 'application/x-ms-shortcut'
        - 'application/x-msdos-program'
        - 'application/x-msdownload'
        - 'application/x-python-code'
        - 'application/x-sh'
condition: selection_suspicious_tld and 1 of selection_malicious_*

False positives (as the rule lists them)

• Rare legitimate software downloads from low quality TLDs

Tags

• attack.initial-access
• attack.command-and-control

References

• https://www.howtogeek.com/137270/50-file-extensions-that-are-potentially-dangerous-on-windows
• https://www.spamhaus.org/reputation-statistics/cctlds/domains/

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/network/zeek/zeek_http_susp_file_ext_from_susp_tld.yml