fix: FPs on docker images #5780
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nasbench
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Nov 28, 2025
rules/linux/file_event/file_event_lnx_persistence_cron_files.yml
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nasbench
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@marius-benthin these are not comment targeted towards you. But are more targeted towards me and other maintainers. For potential improvements. Ofc feel free to take them and improve if you have time.
rules/linux/file_event/file_event_lnx_persistence_cron_files.yml
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Do your things @nasbench. I'll give the rule a tweak afterwards to increase coverage (more include paths) but also add the default cron jobs as filters for the distributions that I have lying around. |
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Pull request overview
This PR fixes false positives in the Linux cron file detection rule by adding filters for legitimate cron file creation on official Docker images (golang, postgres, python, redis, ruby). The rule has been enhanced with comprehensive filtering logic and improved documentation.
Key changes:
- Added extensive filters for package managers, containers, configuration management tools, and system services
- Added specific filters for legitimate cron files commonly found in Docker images
- Enhanced rule description with investigation guidance and false positive reduction recommendations
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swachchhanda000
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Dec 10, 2025
nasbench
reviewed
Dec 10, 2025
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| filter_optional_package_managers: | ||
| Image: | ||
| - '/bin/dpkg' | ||
| - '/usr/bin/dpkg' | ||
| - '/bin/microdnf' | ||
| - '/usr/bin/microdnf' | ||
| - '/bin/rpm' | ||
| - '/usr/bin/rpm' | ||
| - '/bin/yum' | ||
| - '/usr/bin/yum' | ||
| - '/bin/dnf' | ||
| - '/usr/bin/dnf' | ||
| - '/bin/dnf-automatic' | ||
| - '/usr/bin/dnf-automatic' | ||
| - '/bin/pacman' | ||
| - '/usr/bin/pacman' | ||
| - '/usr/bin/dpkg-divert' | ||
| - '/bin/dpkg-divert' | ||
| - '/sbin/apk' | ||
| - '/usr/sbin/apk' | ||
| - '/usr/local/sbin/apk' | ||
| - '/usr/bin/apt' | ||
| - '/usr/sbin/pacman' | ||
| - '/usr/bin/pamac-daemon' | ||
| - '/bin/pamac-daemon' | ||
| filter_optional_containers: | ||
| Image: | ||
| - '/bin/dockerd' | ||
| - '/usr/bin/dockerd' | ||
| - '/usr/sbin/dockerd' | ||
| - '/usr/local/bin/dockerd' | ||
| - '/bin/snapd' | ||
| - '/usr/bin/snapd' | ||
| - '/bin/podman' | ||
| - '/usr/bin/podman' | ||
| - '/kaniko/kaniko-executor' | ||
| filter_optional_config_management: | ||
| Image: | ||
| - '/usr/bin/puppet' | ||
| - '/bin/puppet' | ||
| - '/opt/puppetlabs/puppet/bin/puppet' | ||
| - '/opt/puppetlabs/puppet/bin/ruby' | ||
| - '/usr/bin/chef-client' | ||
| - '/bin/chef-client' | ||
| filter_optional_cloud_agents: | ||
| Image: | ||
| - '/opt/elasticbeanstalk/bin/platform-engine' | ||
| - '/usr/bin/pvedaemon' | ||
| filter_optional_system_services: | ||
| Image: | ||
| - '/usr/libexec/platform-python' | ||
| - '/usr/lib/systemd/systemd' | ||
| - '/usr/sbin/anacron' | ||
| filter_optional_security_tools: | ||
| Image: | ||
| - '/opt/imunify360/venv/bin/python3' | ||
| - '/opt/eset/efs/lib/utild' | ||
| filter_optional_cpanel: | ||
| Image: | ||
| - '/bin/autossl_check' | ||
| - '/usr/bin/autossl_check' | ||
| filter_optional_special_paths: | ||
| Image|startswith: | ||
| - '/nix/store/' | ||
| - '/var/lib/dpkg/' | ||
| - '/tmp/vmis.' | ||
| - '/snap/' | ||
| - '/dev/fd/' | ||
| - '/usr/libexec/platform-python' | ||
| - '/var/lib/waagent/Microsoft' | ||
| filter_optional_special_files: | ||
| TargetFilename|contains: | ||
| - '/var/spool/cron/crontabs/tmp.' | ||
| - '/etc/cron.d/jumpcloud-updater' | ||
| filter_optional_extensions: | ||
| TargetFilename|endswith: | ||
| - '.swp' | ||
| - '.swpx' | ||
| - '.swx' | ||
| - '.dpkg-remove' | ||
| - '.dpkg-new' | ||
| filter_optional_legit_cron: | ||
| # Note: FPs on docker images: golang, postgres, python, redis, ruby | ||
| TargetFilename: | ||
| - '/etc/cron.daily/apt' | ||
| - '/etc/cron.daily/dpkg' | ||
| - '/etc/cron.daily/passwd' | ||
| - '/etc/crontabs/root' | ||
| filter_optional_automation_tools: | ||
| Image|endswith: | ||
| - '/executor' | ||
| - '/cf-agent' | ||
| - '/schedd' | ||
| filter_optional_system_agents: | ||
| Image|endswith: | ||
| - '/droplet-agent.postinst' | ||
| - '/jumpcloud-agent' | ||
| - '/crio' | ||
| filter_optional_security_processes: | ||
| Image|endswith: | ||
| - '/imunify-notifier' | ||
| - '/utild' | ||
| filter_optional_package_operations: | ||
| Image|endswith: '/dnf_install' | ||
| filter_optional_editor_temp: | ||
| Image|endswith: '/sed' | ||
| TargetFilename|startswith: 'sed' | ||
| filter_optional_perl_temp: | ||
| Image|endswith: '/perl' | ||
| TargetFilename|startswith: 'e2scrub_all.tmp' | ||
| filter_optional_vi_backup: | ||
| Image|endswith: | ||
| - '/vi' | ||
| - '/vim' |
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This is all not needed. The purpose is to know when a cron file is created. Hence FP filters should be left to only system level procs
nasbench
reviewed
Dec 10, 2025
| @@ -1,12 +1,21 @@ | |||
| title: Persistence Via Cron Files | |||
| title: Creation of New Cron Files | |||
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Suggested change
| title: Creation of New Cron Files | |
| title: New Cron File Created |
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Summary of the Pull Request
Fixes false positives on official Docker images:
Changelog
fix: Cron Pathes - filter legit cron filepathes
Example Log Event
Fixed Issues
SigmaHQ Rule Creation Conventions