This post was published shortly after the attack was made public. Additional research has been done by multiple security professionals since then, to better understand the logic used by the malware and to filter out false positives. These sources are referenced throughout this post.
UPDATE 2020-12-19 23:20 UTC: updated results table
UPDATE 2020-12-21 15:37 UTC: updated section on C2 infrastructure based on current findings
UPDATE 2020-12-22 17:04 UTC: added link to Invoke-SunburstDecoder
UPDATE 2020-12-22 22:48 UTC: added section: Disabling security services and avoiding detection
UPDATE 2020-12-23 17:33 UTC: updated results table
UPDATE 2021-01-26 13:00 UTC: clarified some of the statements about targeted organizations, as they are only assumptions.
This post provides a list of internal names of organizations that had the SUNBURST backdoor installed, as well as which of these organizations have indications of having proceeded to the second stage of the attack, where further internal compromise might have taken place.
The recent SolarWinds Orion hack is part of a cyber attack that is one of the most severe in history.
A supply chain attack leveraged SolarWinds Orion updates to deliver a backdoor to potentially 18,000 SolarWinds customers. The attack was highly sophisticated.
The infected systems in the various compromised organizations were configured to probe the threat actor systems to request instructions.
Truesec Threat Intelligence analyzed the malware, as well as historical network data, to determine some of the affected organizations that the threat actor might have explicitly selected for further activities, where it is possible that further internal compromise took place. These assumptions are based on historical network data (passive DNS) and the logic within the malware when handling certain responses.
While this is likely only a small part of the scope of the attack, it provides indications on the type of organizations that were potentially the real targets of the attack.
Some names stand out, such as ggsg-us.cisco (Cisco GGSG), us.deloitte.co (Deloitte), nswhealth.net (NSW Ministry of Health in Australia), banccentral.com (service supplier of IT and security for banks), and many others.
The impact of this attack is likely to be of gigantic proportions. The full extent of this breach will most likely never be communicated to the public, and instead will be restricted to trusted parts of the intelligence community.
A supply chain attack leveraged SolarWinds to deliver malicious software updates to their customers (approximately 18.000 potentially affected customers according to SolarWinds). The update installed a sophisticated backdoor giving the threat actor the ability to access selected targets and proceed with further activities inside the compromised organizations.
It is believed that the attack was carried out by a nation-state actor, likely APT29 a.k.a. Cozy Bear, i.e. Russian Intelligence.
FireEye and Microsoft initially published reports describing some of the inner workings of the backdoor. A second, more detailed, post was later published by FireEye. The backdoor is remarkably sophisticated and is worth a long technical description, while only some of its functionalities and characteristics are described in this article.
Truesec Threat Intelligence analyzed the backdoor as well as historical network data to identify patterns revealing possible victims.
Due to the nature of the attack, a large number of organizations around the world have been affected by the backdoor, while likely only a smaller number were specifically selected and targeted by the threat actor to conduct additional internal compromise (phase 2).
The threat actor was able to inject a backdoor in the Solarwinds Orion software by modifying the source code of an existing plugin, which was then signed by Solarwinds and published as part of an update available on the SolarWinds website. SolarWinds published an advisory specifying the versions affected.
The malicious update has been available for several months and there are indications of breaches as early as March 2020. One of the identified malicious updates was hosted at the following URL:
The update package was properly digitally-signed, as shown below.
The backdoor code was made part of the following digitally-signed Orion component:
This DLL is also signed.
The backdoor implements sophisticated functionality to communicate with the threat actor infrastructure and applies logic to determine what actions should be taken.
As a large number of Orion servers around the world have been infected with the backdoor, the threat actor had to have a way to determine which organization was contacting the attack infrastructure to be able to select the real target of this attack. This logic is partially explained below. For details see the FireEye article .
The hacked servers that received the Solarwinds backdoor periodically probe the threat actor infrastructure with a DNS query like the following:
where <DGA_value> is computed with a DomainName Generation Algorithm and contains an encoded version of the internal Active Directory name of the infected server. The threat actor server decodes the information in the DNS requests and uses the internal domain name of the organization to determine what instructions to send back.
Truesec reversed the backdoor and identified a set of IP address ranges that, when received as part of the DNS response, will determine the actions taken by the backdoor code. Part of this code is illustrated in the figure below.
The AddressFamily field determines what the backdoor should do next, which can be roughly summarized as follows:
Atm or ImpLink : Terminate (killswitch).
Ipx : Go to initial state and keep polling.
NetBios: Start or continue second stage. Can initialize an HTTP backdoor channel used to collect additional information and deploy a second stage malware (specified by the threat actor at the time of instructions, and therefore specific to the target).
We can therefore assume that if the initial probe was answered with an address of type NetBios, the threat actor had configured the backdoor to move to the second stage, which is where additional malware can be deployed to possibly perform additional internal compromise.
Given the number of affected organizations, it is still likely that a large number of victims with indications of stage 2, as described here, were later filtered out by the threat actor (not deemed worthy of further attack).
Identifying Internal Names of Victims
The DomainName Generation Algorithm described earlier, used to create a DNS query containing an encoded value of the internal domain name of the compromised organization, can be reversed.
RedDrip Team published a report and a script to decode the DGA part of the DNS requests, therefore allowing to retrieve the cleartext value of the internal domain name of the hacked server that made the request.
For example, if a compromised server makes the following request to the threat actor server:
This can be decoded to obtain the following internal name of the victim:
This means that having records of performed DNS requests to avsvmcloud[.]com will reveal the internal names of the compromised organizations.
The SUNBURST backdoor uses the following three parameters to create a "Host Id" used in the DNS requests:
- MAC address of the network interface
- Internal domain name that the machine is joined to
- Machine Guid from HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography\MachineGuid
Since the DGA values from DNS requests can be decoded, if you have a DNS request and you want to see if it was generated from a certain machine, you only need to know MAC address, internal domain name, and machine Guid.
This can be extremely helpful during investigations to determine if a machine had a communicating SUNBURST backdoor on it. We wrote a PowerShell script that can be used for this, based on the great work by Erik Hjelmvik, Netresec.
Identifying Threat Actor Instructions
The next step was to obtain historical records of DNS requests, including the response. We obtained some of the available historical data.
The sample data contains 1528 DNS requests to avsvmcloud[.]com and their responses.
When filtered for requests matching the DGA algorithm syntax, we have requests with dates ranging from early April to December 2020.
This is an example of such request and response:
date : 2020-04-19 08:24:26 last_seen : 2020-04-19 08:24:27 qtype : 1 domain : avsvmcloud.com qname : q8bps26mocuq6re4dutru70ct2w.appsync-api.us-east-1.avsvmcloud.com value_ip : 22.214.171.124 type : ip _key : 0e8ab64d5f5aff04fea862f4f72fcf1d04c3d377 value : 126.96.36.199
From this data we can determine that on April 19th, a request was made that decodes to the internal name pageaz.gov, and received as response 188.8.131.52, which according to the backdoor logic explained earlier maps to address type NetBios, meaning that the threat actor might have deployed an HTTP backdoor in this environment.
Command and Control Infrastructure
By analyzing the IP addresses returned when instructing infected servers to establish an HTTP backdoor, we can identify the following blocks.
|IP block||Registered Organization (WHOIS information)|
|184.108.40.206 / 255.254.0.0||Amazon.com, Inc.|
|220.127.116.11 / 255.255.255.0||Amazon.com, Inc.|
|18.104.22.168 / 255.255.254.0||Amazon Inc.|
|22.214.171.124 / 255.255.248.0||Amazon Data Services Ireland DUB3 Datacentre|
|126.96.36.199 / 255.255.0.0||Amazon Technologies Inc.|
|188.8.131.52 / 255.255.0.0||Amazon Data Services Canada|
|184.108.40.206 / 255.255.255.0||Traiana, Inc|
These IP blocks are not used to establish the HTTP connection. Instead, if a CNAME record is contained in the response, that is the address used as C2 address for the new HTTP channel. FireEye listed the CNAME responses that they have observed as part of their indicators of compromise. These are also reported below for convenience:
freescanonline[.]com deftsecurity[.]com freescanonline[.]com thedoccloud[.]com
We initially thought that the A records in the blocks above were the C2 addresses, which would also make sense as almost all are part of the Amazon infrastructure and threat actors often use cloud providers to host their attack infrastructure. This would have also meant that the block belonging to Traiana, Inc could potentially be under the control of the threat actor.
Truesec Threat Intelligence observed a large number of DNS responses from the threat actor server providing different IP addresses in the range 220.127.116.11/24 for the next stage.
At this point in time, it does not seem that these IP blocks were under the control of the threat actor, but were instead deliberately used as part of the logic within the backdoor.
Putting the Pieces Together
We have decoded the DGA parts of the requests to identify internal domain names of compromised organizations, correlated that with the responses received from the threat actor server, and mapped them with the hardcoded list of IP ranges in the backdoor code.
This gives us a (partial) list of breached organizations, and which ones had the SUNBURST backdoor configured for the second stage of the attack where further internal compromise might have taken place.
Note that some of the names are truncated. Further analysis is ongoing to determine if this can be improved.
The results are summarized at the bottom of this post. This list contains the decoded values of internal domain names. We can therefore only assume that they belong to an organization based on the name of the domains and publicly available information.
Some of the internal names stand out, such as ggsg-us.cisco (Cisco GGSG), us.deloitte.co (Deloitte), nswhealth.net (NSW Ministry of Health in Australia), banccentral.com (service supplier of IT and security for banks), and many others.
Disabling Security Services and Avoiding Detection
The backdoor keeps an eye on a number of processes, services, and device drivers. It simply avoids running if any of the following 137 processes are detected on the system.
apimonitor-x64 apimonitor-x86 autopsy64 autopsy autoruns64 autoruns autorunsc64 autorunsc binaryninja blacklight cutter de4dot debugview diskmon dnsd dnspy dotpeek32 dotpeek64 dumpcap exeinfope fakedns fakenet ffdec fiddler fileinsight floss gdb hiew32 idaq64 idaq idr ildasm ilspy jd-gui lordpe officemalscanner ollydbg pdfstreamdumper pe-bear pebrowse64 peid pe-sieve32 pe-sieve64 pestudio peview pexplorer ppee ppee procdump64 procdump processhacker procexp64 procexp procmon prodiscoverbasic py2exedecompiler r2agent rabin2 radare2 ramcapture64 ramcapture reflector regmon resourcehacker retdec-ar-extractor retdec-bin2llvmir retdec-bin2pat retdec-config retdec-fileinfo retdec-getsig retdec-idr2pat retdec-llvmir2hll retdec-macho-extractor retdec-pat2yara retdec-stacofin retdec-unpacker retdec-yarac rundotnetdll sbiesvc scdbg scylla_x64 scylla_x86 shellcode_launcher solarwindsdiagnostics sysmon64 sysmon tcpdump tcpvcon tcpview vboxservice win32_remote win64_remotex64 windbg windump winhex64 winhex winobj wireshark x32dbg x64dbg xwforensics64 xwforensics redcloak avgsvc avgui avgsvca avgidsagent avgsvcx avgwdsvcx avgadminclientservice afwserv avastui avastsvc aswidsagent aswidsagenta aswengsrv avastavwrapper bccavsvc psanhost psuaservice psuamain avp avpui ksde ksdeui tanium taniumclient taniumdetectengine taniumendpointindex taniumtracecli taniumtracewebsocketclient64
The second check is a list of 8 services matched by process names. The backdoor searches for the services and keeps track of the status of the services. Additionally, it changes the security descriptor of the service registry key and the start parameter. The service is never stopped by the backdoor and it looks like it simply waits until the machine restarts for the service to change state. The state of the services is recorded and stored in the DLL config file using the parameter RetryWatcherPostpone
The list of services is the following:
msmpeng mssense cavp cb csfalconservice csfalconcontainer xagt xagtnotif ekrn eguiproxy egui fsgk32st fswebuid fsgk32 fsma32 fssm32 fnrb32 fsaua fsorsp fsav32
The backdoor avoids tampering with the start parameter of the WinDefend service and only changes the service key security descriptor.
The third check is performed to detect 17 specific device drivers. This check behaves the same way as the check for processes and will make sure that the backdoor aborts if any of the following drivers are detected.
cybkerneltracker.sys atrsdfw.sys eaw.sys rvsavd.sys dgdmk.sys sentinelmonitor.sys hexisfsmonitor.sys groundling32.sys groundling64.sys safe-agent.sys crexecprev.sys psepfilter.sys cve.sys brfilter.sys brcow_x_x_x_x.sys lragentmf.sys libwamf.sys
Based on this analysis, we can conclude that the detection of any of the specified processes or device drivers will always alter the execution path of the backdoor and discontinue the execution. While the detection of the listed services will only alter the execution path if a change in the status was detected.
Note that for services running as protected services, changing the service registry start parameter is not possible while the service is running. This applies to services related to any antimalware with ELAM capabilities like the Windows Defender.
The Backdoor does not try to avoid the listed antivirus, antimalware, and EDR service. For unknown reasons, it tries to keep track of the status of these services.
Impact of the Attack
The target organizations, the threat actor sophistication, and the amount of time between the initial breach and the discovery strongly indicates an impact of gigantic proportions.
It is highly likely that a massive amount of highly confidential information belonging to government organizations, medical institutions, cybersecurity, the financial industry, etc. has been leaked. It is also highly likely that software and systems have been compromised and that the modus operandi of the SolarWinds breach can be repeated in future campaigns.
More information will be disclosed during the upcoming months but the full extent of this breach will most likely never be communicated to the public, and instead will be restricted to trusted parts of the intelligence community.
Results of the Analysis
|Decoded Internal Name||Possible Organization|
(may be inaccurate)*
|corp.stratusnet||Stratus Networks||2nd stage||2020-04-17|
|pageaz.gov||City of Page||2nd stage||2020-04-19|
|christieclinic.com||Christie Clinic Telehealth||2nd stage||2020-04-22|
|resprod.com||Res Group (Renewable energy company)||2nd stage||2020-05-06|
|barrie.ca||City of Barrie||2nd stage||2020-05-13|
|te.nz||TE Connectivity (Sensor manufacturer)||2nd stage||2020-05-13|
|fisherbartoninc.com||The Fisher Barton Group (Blade Manufacturer)||2nd stage||2020-05-15|
|sdch.local||South Davis Community Hospital||2nd stage||2020-05-18|
|mnh.rg-law.ac.il||College of Law and Business, Israel||2nd stage||2020-05-26|
|magnoliaisd.loc||Magnolia Independent School District||2nd stage||2020-06-01|
|fidelitycomm.lo||Fidelity Communications (ISP)||2nd stage||2020-06-02|
|corp.stingraydi||Stingray (Media and entertainment)||2nd stage||2020-06-03|
|keyano.local||Keyano College||2nd stage||2020-06-03|
|nswhealth.net||NSW Health||2nd stage||2020-06-12|
|city.kingston.on.ca||City of Kingston, Ontario, Canada||2nd stage||2020-06-15|
|corp.ptci.com||Pioneer Telephone Scholarship Recipients||2nd stage||2020-06-19|
|ironform.com||Ironform (metal fabrication)||2nd stage||2020-06-19|
|digitalsense.co||Digital Sense (Cloud Services)||2nd stage||2020-06-24|
|ggsg-us.cisco||Cisco GGSG||2nd stage||2020-06-24|
|signaturebank.l||Signature Bank||2nd stage||2020-06-25|
|mountsinai.hosp||Mount Sinai Hospital||2nd stage||2020-07-02|
|pqcorp.com||PQ Corporation||2nd stage||2020-07-02|
|mountsinai.hospital||Mount Sinai Hospital, New York||2nd stage||2020-07-02|
|banccentral.com||BancCentral Financial Services Corp.||2nd stage||2020-07-03|
|kcpl.com||Kansas City Power and Light Company||2nd stage||2020-07-07|
|lufkintexas.net||Lufkin (City in Texas)||2nd stage||2020-07-07|
|sm-group.local||SM Group (Distribution)||2nd stage||2020-07-07|
|cys.local||CYS Group (Marketing analytics)||2nd stage||2020-07-10|
|oslerhc.org||William Osler Health System||2nd stage||2020-07-11|
|wrbaustralia.ad||W. R. Berkley Insurance Australia||2nd stage||2020-07-11|
|dufferincounty.on.ca||Dufferin County, Ontario, Canada||2nd stage||2020-07-17|
|fmtn.ad||City of Farmington||2nd stage||2020-07-21|
|pcsco.com||Professional Computer Systems||2nd stage||2020-07-23|
|camcity.local||Adult Webcam||2nd stage||2020-07-28|
|usd373.org||Newton Public Schools||2nd stage||2020-08-01|
|sfsi.stearnsban||Stearns Bank||2nd stage||2020-08-02|
|ville.terrebonn||Ville de Terrebonne||2nd stage||2020-08-02|
|itps.uk.net||ITPS (IT Services)||2nd stage||2020-08-11|
|prod.hamilton.||Hamilton Company||2nd stage||2020-08-19|
|cosgroves.local||Cosgroves (Building services consulting)||2nd stage||2020-08-25|
|moncton.loc||City of Moncton||2nd stage||2020-08-25|
|cds.capilanou.||Capilano University||2nd stage||2020-08-27|
|csnt.princegeor||City of Prince George||2nd stage||2020-09-18|
|netdecisions.lo||Netdecisions (IT services)||2nd stage||2020-10-04|
|mixonhill.com||Mixon Hill (intelligent transportation systems)||Terminate||2020-04-29|
|yorkton.cofy||Community Options for Families & Youth||Terminate||2020-05-08|
|spsd.sk.ca||Saskatoon Public Schools||Terminate||2020-06-12|
|bcofsa.com.ar||Banco de Formosa||Terminate||2020-07-13|
|ansc.gob.pe||GOB (Digital Platform of the Peruvian State)||Terminate||2020-07-25|
|bop.com.pk||The Bank of Punjab||Terminate||2020-07-31|
|rbe.sk.ca||Regina Public Schools||Terminate||2020-08-20|
|phabahamas.org||Public Hospitals Authority, Caribbean||Terminate||2020-11-05|
|insead.org||INSEAD Business School||Terminate||2020-11-07|
|bisco.int||Bisco International (Adhesives and tapes)||Unknown||2020-04-30|
|xnet.kz||X NET (IT provider in Kazakhstan)||Unknown||2020-06-09|
|e-idsolutions.||IDSolutions (video conferencing)||Unknown||2020-07-16|
|ad.azarthritis.com||Arizona Arthritis & Rheumatology Associates||N/A||N/A|
|ad.optimizely.||Optimizely, Software Company||N/A||N/A|
|central.pima.gov||Pima County, Arizona||N/A||N/A|
|cityofsacramento||City of Sacramento||N/A||N/A|
|clinicasierravista.org||Clinica Sierra Vista||N/A||N/A|
|helixwater.org||Helix Water District||N/A||N/A|
|mutualofomahabank.com||Mutual of Omaha Bank||N/A||N/A|
|SamuelMerritt.edu||Samuel Merritt University||N/A||N/A|
|siskiyous.edu||College of the Siskiyous, California||N/A||N/A|
|vantagedatacenters.local||Vantage Data Centers||N/A||N/A|
* The organization names are assumptions based on the decoded internal names and may be inaccurate.
For additional information and discussions on this topic, Truesec has recently published the following video where we discuss nation-state actors in relation to the SolarWinds SUNBURST hack.
I was interviewed by Andy Syrewicze at Altaro on the SolarWinds SUNBURST attack and what IT service providers can and should do. You can watch the video interview below and you can also read Andy's post here.