README.md

xnumon - monitor macOS for malicious activity

https://www.roe.ch/xnumon

Overview

xnumon is a monitoring agent that produces system activity logs intended to be suitable for monitoring potentially large fleets of macOS systems for malware and intrusions. It aims at providing similar capabilities on macOS that sysmon provides on Windows.

Currently implemented are the following log events:

• xnumon-ops[0] and xnumon-stats[1] for in-band monitoring of agent status and activity metrics.
• exec-image[2]: a process has replaced its executable image as a result of calling one of the execve(2) or posix_spawn(2) family syscalls.
• process-access[3]: a process has accessed and possibly manipulated another process using either the task_for_pid or ptrace(2) syscalls.
• launchd-add[4]: a process has added or modified a launch daemon or launch agent plist.

xnumon provides context information such as executable image hashes, code signing meta-data, script shebang handling, and the history of previous executable images that led to the current process state. It does so by tracking fork and other syscalls instead of relying only on the ppid, which can change over the lifetime of a process.

Requirements

A supported version of OS X or macOS, currently:

• OS X 10.11 El Capitan
• macOS 10.12 Sierra
• macOS 10.13 High Sierra

Documentation

More complete documentation has yet to be written. Some useful commands:

• cat /var/log/xnumon.log | jq 'select(.eventcode==0)'
• xnumonctl
• xnumon -h
• dmesg | grep xnumon

Installing

The installer package will install the daemon, the control utility and a default configuration which by default will log to /var/log/xnumon.log in JSON Lines format. It will also install a matching newsyslog configuration and the optional kernel extension. The kernel extension is currently unsigned and as such will not be usable in production environments unless you control a kext signing certificate (see «Kernel Extension» below).

The extensively commented default configuration is installed to /Library/Application Support/ch.roe.xnumon/configuration.plist-default. While the defaults are as sensible as possible, you will most likely want to maintain a custom configuration at /Library/Application Support/ch.roe.xnumon/configuration.plist to be used in favour of the default configuration.

In addition to installing xnumon, you will want to make sure that auditd does not clobber the global kernel audit policy. Make sure the argv policy flag is enabled in /etc/security/audit_control, which is the default. Right now, xnumon does not process the additional information provided by the arge flag, but most likely will start doing so in a future release.

In order to make the logs useful and to get them out of reach of malware and attackers, it is recommended to continuously forward logs to central log collection infrastructure. A sample Splunk configuration for ingesting xnumon logs can be found in extra/splunk.

Kernel Extension

The xnumon kext is optional and provides reliable acquisition of image hashes and code signing information even for short-living images using the Kauth KPI. The kernel extension is currently unsigned and therefore cannot be deployed unless you own a kernel signing certificate. A kernel signing certificate for xnumon has been requested from Apple, but has not been approved yet.

To load the unsigned kext for testing and development, you need to disable System Integrity Protection (SIP) for kexts. Reboot to repair mode by pressing cmd⌘+r during boot and from within the repair console, run csrutil enable --without kext. This will also turn off the kext user consent requirement of High Sierra.

Uninstalling

xnumonctl uninstall

This will remove all traces of this package from your system, including logs at the default location /var/log/xnumon.log*, but not including the config at /Library/Application Support/ch.roe.xnumon/configuration.plist unless it is the same as the default config.

Build Dependencies

Building an unsigned userland binary and kernel extension requires Xcode command line tools. The userland binary requires only the CoreFoundation and Security frameworks and libbsm; there are no third-party dependencies.

Building a signed userland binary requires an Application Developer ID certificate.

Building a signed kernel extension requires an Kext Developer ID certificate.

Building signed binary packages requires pandoc and an Installer Developer ID certificate.

Copyright and License

Copyright (c) 2017-2018, Daniel Roethlisberger.
All rights reserved.
Licensed under the Open Software License version 3.0.
Contains components licensed under BSD and MIT licenses.

See LICENSE, LICENSE.contrib and LICENSE.third as well as the respective source file headers for details.