NETRESEC Network Security Blog - Tag : pDNS


Twenty-three SUNBURST Targets Identified

Remember when Igor Kuznetsov and Costin Raiu announced that two of the victims in FireEye's SUNBURST IOC list were ***net.***.com and central.***.gov on Kaspersky's Securelist blog in December? Reuters later reported that these victims were Cox Communications and Pima County.

We can now reveal that the internal AD domain of all SUNBURST deployments in FireEye's IOC list can be extracted from publicly available DNS logs published by twitter user VriesHd, a.k.a. "Kira 2.0", with help of our SunburstDomainDecoder tool. The data published by VriesHd is the most complete SUNBURST DNS collection we've seen, with over 35.000 avsvmcloud.com subdomains! Here is FireEye's IOC table completed with our findings:

Leaked AD Domain Sunburst C2 FQDN Stage 2 CNAME Timestamp (UTC)
central.pima.gov 6a57jk2ba1d9keg15cbg.appsync-api.eu-west-1.avsvmcloud.com freescanonline[.]com 2020-06-13 09:00
central.pima.gov 7sbvaemscs0mc925tb99.appsync-api.us-west-2.avsvmcloud.com deftsecurity[.]com 2020-06-11 22:30
central.pima.gov gq1h856599gqh538acqn.appsync-api.us-west-2.avsvmcloud.com thedoccloud[.]com 2020-06-13 08:30
coxnet.cox.com ihvpgv9psvq02ffo77et.appsync-api.us-east-2.avsvmcloud.com freescanonline[.]com 2020-06-20 02:30
corp.qualys.com k5kcubuassl3alrf7gm3.appsync-api.eu-west-1.avsvmcloud.com thedoccloud[.]com 2020-07-22 17:00
corp.qualys.com mhdosoksaccf9sni9icp.appsync-api.eu-west-1.avsvmcloud.com thedoccloud[.]com 2020-07-23 18:30

Victims Targeted with SUNBURST Stage 2 Backdoor

It was not just the victims listed in FireEye's IOC that were specifically targeted by the SUNBURST operators. As explained in our Finding Targeted SUNBURST Victims with pDNS blog post, the "STAGE2" flag in SUNBURST's DNS beacons can be used to reveal additional organizations that were singled out as interesting targets by the threat actors.

We'd like to stress that the majority of all companies and organizations that have installed a backdoored SolarWinds Orion update were never targeted by the threat actors. This means the these SUNBURST backdoors never made it past what we call "Stage 1 operation", where the backdoor encodes the internal AD domain name and installed security products into DNS requests. SUNBURST backdoors in Stage 1 operation cannot accept any commands from the C2 server without first progressing into Stage 2 operation. We estimate that about 99.5% of the installed SUNBURST backdoors never progressed into Stage 2 operation.

Here is the full list of internal AD domain names from the SUNBURST deployments in VriesHd's DNS data that actually did enter Stage 2 operation according to our analysis: 23 SUNBURST Targets Identified

Our SUNBURST STAGE2 Victim Table has now been updated with additional details about the STAGE2 signaling from these SUNBURST implants, including timestamps, avsvmcloud.com subdomains and GUID values.

Initial Microsoft Targeting FAIL

The last two entries in the AD domain list above are interesting, since they both hint that the targeted entity might be Microsoft.

The data that gets exfiltrated in DNS beacons during SUNBURST's initial stage is the internal domain the SolarWinds Orion PC is connected to and a list of installed security products on that PC. These domain names, security products and possibly also the victims' public IP addresses, was the data available to the attackers when they decided which ones they wanted to proceed to Stage 2 with and thereby activate the HTTPS backdoor built into SUNBURST.

The threat actors were probably surprised when they realized that "WincoreWindows.local" was in fact a company in West Virginia that manufactures high quality windows and doors.

Wincore Windows and Doors

The threat actors later found another backdoored SolarWinds Orion machine connected to a domain called "wctc.msft", which also sounds like it could be Microsoft. Below is a table outlining relevant events for these two SUNBURST deployments that can be extracted from VriesHd's SB2 spreadsheet with SunburstDomainDecoder.

Target ID Beaconed Data Date
A887B592B7E5B550 AD domain part 1: "WincoreW"
A887B592B7E5B550 AD domain part 2: "indows.local"
A887B592B7E5B550 AV Products: [none] 2020-05-22
🤔 Threat actor decision: Target victim A887B592B7E5B550
A887B592B7E5B550 STAGE2 request for new C2 server in CNAME 2020-05-26
🤔 Threat actor decision: These aren't the droids we're looking for
59956D687A42F160 AD domain: "wctc.msft"
59956D687A42F160 AV Products: [none] 2020-06-20
59956D687A42F160 Ping 2020-06-21
59956D687A42F160 Ping 2020-06-22
🤔 Threat actor decision: Target victim 59956D687A42F160
59956D687A42F160 STAGE2 request for new C2 server in CNAME 2020-06-23

Microsoft have been public about being hit by SUNBURST (or "Solorigate" as they call it), so we can assume that the threat actors eventually located a backdoored SolarWinds Orion installation in their networks.

Victim Notification

We spent the previous week reaching out to targeted companies and organizations, either directly or through CERT organizations. From what we understand many of these organizations were already aware that they had been targeted victims of SUNBURST, even though they might not have gone public about the breach.

The Ethical Dilemma

We have no intentions to shame the organizations that have installed a backdoored SolarWinds Orion update, regardless if they were targeted by the threat actor or not. In fact, the supply chain security problem is an extremely difficult one to tackle, even for companies and organizations with very high security standards. This could have happened to anyone!

However, since multiple passive DNS logs and SUNBURST victim lists have been circulating through publicly available channels for over a month, we felt that it was now acceptable to publicly write about the analysis we've been doing based on all this data. We'd also like to thank everyone who has helped collect and share passive DNS data, including John Bambenek, Joe Słowik, Rohit Bansal, Dancho Danchev , Paul Vixie and VriesHd. This open data has been crucial in order to develop and verify our SunburstDomainDecoder tool, which has been leveraged by numerous incident response teams to perform forensic analysis of DNS traffic from their SolarWinds Orion deployments.

More Credits

We'd like to thank CERT-SE and all other computer emergency response organizations that have helped us with the task of notifying organizations that were identified as targeted. We would also like to applaud companies and organizations like FireEye, Palo Alto Networks, Fidelis Cybersecurity, Microsoft, the U.S. Department of Energy and the U.S. Federal Courts for being transparent and publicly announcing that the SUNBURST backdoor had been used in an attempt to compromise their networks.

Posted by Erik Hjelmvik on Monday, 25 January 2021 08:25:00 (UTC/GMT)

Tags: #SUNBURST #FireEye #Solorigate #Microsoft #SolarWinds #FireEye #CNAME #STAGE2 #DNS #Passive DNS #avsvmcloud.com #pDNS #Microsoft

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Finding Targeted SUNBURST Victims with pDNS

Our SunburstDomainDecoder tool can now be used to identify SUNBURST victims that have been explicitly targeted by the attackers. The only input needed is passive DNS (pDNS) data for avsvmcloud.com subdomains.

Companies and organizations that have installed trojanized a SolarWinds Orion update containing the SUBURST backdoor will send DNS queries for seemingly random subdomains of avsvmcloud.com. Some of these DNS queries actually contain the victim's internal AD domain encoded into the subdomain, as explained in our blog post Reassembling Victim Domain Fragments from SUNBURST DNS.

Three Stages of SUNBURST Backdoor Operation

Most SUNBURST victims were luckily not targeted by the attackers. This means that the backdoor never made it past "STAGE1" of the infection process. Nevertheless, the attackers did choose to proceed to "STAGE2" with some victims. As explained in FireEye's blog post SUNBURST Additional Technical Details, the "C2 coordinator" can proceed to the next stage by responding with a DNS A record pointing to an IP address within any of these three ranges:

  • 18.130.0.0/16
  • 99.79.0.0/16
  • 184.72.0.0/15

According to FireEye's "Diagram of actor operations and usage of SUNBURST", the decision to proceed to the next stage is based upon whether or not the victim's internal AD domain is "interesting to attack".

Note: "STAGE2" is referred to as "associated mode" in FireEye's blog post.

SUNBURST backdoors that have entered STAGE2 will allow CNAME records in DNS responses to be used as new C2 domains.

Sunburst stages 1 to 3 (passive, associated and active)

We have discovered that the SUNBURST backdoor actually uses a single bit in the queried avsvmcloud.com subdomain in order to flag that it has entered STAGE2 and is accepting new C2 domains in CNAME records. This bit is called flag, ext or dnssec in the malicious SUNBURST implant and can be extracted from DNS queries that have an encoded timestamp, such as those indicating which security products that are installed.

Detecting STAGE2 DNS Requests

Our SunburstDomainDecoder tool has now been updated to include a "STAGE2" tag in the output for DNS queries containing this stage 2 flag. This means that organizations like national CERTs, who perform incident response coordination and victim notification, can now use SunburstDomainDecoder in order to identify and notify targeted SUNBURST victims that have entered STAGE2.

Here's the output we get when feeding SunburstDomainDecoder with Bambenek's uniq-hostnames.txt passive DNS data and only displaying lines containing "STAGE2":

SunburstDomainDecoder.exe < uniq-hostnames.txt | findstr STAGE2
22334A7227544B1E 2020-09-29T04:00:00.0000000Z,STAGE2 5qbtj04rcbp3tiq8bo6t
FC07EB59E028D3EE 2020-06-13T09:00:00.0000000Z,STAGE2 6a57jk2ba1d9keg15cbg
1D71011E992C3D68 2020-06-11T22:30:00.0000000Z,STAGE2 7sbvaemscs0mc925tb99
F90BDDB47E495629 2020-06-13T08:30:00.0000000Z,STAGE2 gq1h856599gqh538acqn
DB7DE5B93573A3F7 2020-06-20T02:30:00.0000000Z,STAGE2 ihvpgv9psvq02ffo77et
3C327147876E6EA4 2020-07-22T17:00:00.0000000Z,STAGE2 k5kcubuassl3alrf7gm3
3C327147876E6EA4 2020-07-23T18:30:00.0000000Z,STAGE2 mhdosoksaccf9sni9icp
1D71011E992C3D68 central.pima.gov,STAGE2
DB7DE5B93573A3F7 coxnet.cox.com,STAGE2,WindowsDefender
F90BDDB47E495629 central.pima.gov,STAGE2

Most of these subdomains are listed in FireEye's Indicator_Release_NBIs.csv file as having CNAME pointers to other SUNBURST C2 domains like: freescanonline[.]com, deftsecurity[.]com and thedoccloud[.]com. But the first domain, with GUID 22334A7227544B1E, was actually not part of FireEye's IOC data.

Even more STAGE2 domains and GUID values can be found by analyzing other passive DNS resources, such as this passive DNS dump on pastebin by Rohit Bansal.

curl -s https://pastebin.com/raw/6EDgCKxd | SunburstDomainDecoder.exe | findstr STAGE2
E258332529826721 2020-07-18T05:00:00.0000000Z,STAGE2 1dbecfd99ku6fi2e5fjb
2039AFE13E5307A1 2020-05-30T14:30:00.0000000Z,STAGE2 4n4vte5gmor7j9lpegsf
22334A7227544B1E 2020-09-29T04:00:00.0000000Z,STAGE2 5qbtj04rcbp3tiq8bo6t
FC07EB59E028D3EE 2020-06-13T09:00:00.0000000Z,STAGE2 6a57jk2ba1d9keg15cbg
1D71011E992C3D68 2020-06-11T22:30:00.0000000Z,STAGE2 7sbvaemscs0mc925tb99
1D71011E992C3D68 2020-06-11T22:30:00.0000000Z,STAGE2 7sbvaemscs0mc925tb99
F90BDDB47E495629 2020-06-13T08:30:00.0000000Z,STAGE2 gq1h856599gqh538acqn
F90BDDB47E495629 2020-06-13T08:30:00.0000000Z,STAGE2 gq1h856599gqh538acqn
DB7DE5B93573A3F7 2020-06-20T02:30:00.0000000Z,STAGE2 ihvpgv9psvq02ffo77et
DB7DE5B93573A3F7 2020-06-20T02:30:00.0000000Z,STAGE2 ihvpgv9psvq02ffo77et
3C327147876E6EA4 2020-07-23T18:30:00.0000000Z,STAGE2 mhdosoksaccf9sni9icp

After removing the domains already present in FireEye's IOC we're left with the following FQDN's that have been requested by SUNBURST backdoors in STAGE2:

  • 1dbecfd99ku6fi2e5fjb.appsync-api.us-east-1.avsvmcloud.com
  • 4n4vte5gmor7j9lpegsf.appsync-api.eu-west-1.avsvmcloud.com
  • 5qbtj04rcbp3tiq8bo6t.appsync-api.us-east-1.avsvmcloud.com

Update January 7, 2021

Paul Vixie kindly shared his SunburstDomainDecoder output on Twitter yesterday. Paul's results show that the victim with GUID FC07EB59E028D3EE, which corresponds to the "6a57jk2ba1d9keg15cbg.appsync-api.eu-west-1.avsvmcloud[.]com" CNAME entry in FireEye's IOC, was Pima County. This means that 3C327147876E6EA4 is the only GUID among the CNAME records published by FireEye that cannot yet be tied to a victim organization. Paul's data also reveals two new STAGE2 victim GUIDs (65A28A36F24D379D and 8D2267C5A00796DA).

Update January 12, 2021

With help of SunburstDomainDecoder 1.9 and passive DNS data from Dancho Danchev we've been able to verify that Palo Alto have installed the maliocous SUNBURST backdoor and that it entered into STAGE2 opreration on September 29, 2020. Palo Alto's CEO Nikesh Arora has confirmed that they were hit by SUNBURST (or "SolarStorm" as they call it).

Update January 25, 2021

On December 17 VriesHd tweeted a link to a Google Docs spreatsheet containing aggregated SUNBURST DNS request data.

Might be helpfull with the SolarWinds/SUNBURST data to combine one another, so here's all the data (subdomain, region, first seen date, decrypted DGA) that I'm personally aware of in a Google sheet atm. Feel free to comment with new or updated information

One month later VriesHd made some substatial additions to the "SB2" spreadsheet, which by then contained several new STAGE2 victims. We have since then actively been trying to reach out to the targeted organizations, either directly or through CERT organizations, who perform incident response coordination and help with the victim notification process. VriesHd's passive DNS collection has now been incorporated into the SUNBURST STAGE2 Victim Table below.

Targeted SUNBURST Victims

Here's a summary of the STAGE2 beacons from SUNBURST victims that can be extracted from publicly available data:

GUID avsvmcloud.com Subdomain Timestamp (UTC) AD Domain
FF1E34A864BCE106 dh1usc8287hr46bia74a 2020-05-14 14:30 nsanet.local
E5E2AD2B6DE697D6 70fov85qclvubqhf9vlh 2020-05-16 19:30 cisco.com
FF1E34A864BCE106 2die0g7i5kgkki628gaj 2020-05-18 11:30 nsanet.local
3E8DF7FF13FC8D38 7hpaqi751fqoei2fdv8m 2020-05-18 16:30 HQ.FIDELIS
FF1E34A864BCE106 tsem12v1rn620hatfol2 2020-05-20 14:30 nsanet.local
FF1E34A864BCE106 a0hmuoveln2400sfvf6n 2020-05-20 16:30 nsanet.local
0C1A5A27B297FE46 k0biaol9fc84ummfn7vi 2020-05-26 11:30 vgn.viasatgsd.com
A887B592B7E5B550 m4apr0vu9qnomtun3b9t 2020-05-26 20:00 WincoreWindows.local
2039AFE13E5307A1 4n4vte5gmor7j9lpegsf 2020-05-30 14:30 suk.sas.com
06A4EA63C80EE24A 9q5jifedn8aflr4ge3nu 2020-05-31 12:00 scc.state.va.us
9850F550BD1010F2 gth7uravpvaapoi86834 2020-05-31 20:00 lagnr.chevrontexaco.net
E5E2AD2B6DE697D6 8k56mm0b876uvf5e7rd3 2020-06-01 19:00 cisco.com
2039AFE13E5307A1 laog1ushfp80e3f18cjg 2020-06-03 01:30 suk.sas.com
06A4EA63C80EE24A ntlcvjpqc57t9kb8ac75 2020-06-03 23:30 scc.state.va.us
1D71011E992C3D68 7sbvaemscs0mc925tb99 2020-06-11 22:30 central.pima.gov
F90BDDB47E495629 gq1h856599gqh538acqn 2020-06-13 08:30 central.pima.gov
FC07EB59E028D3EE 6a57jk2ba1d9keg15cbg 2020-06-13 09:00 central.pima.gov
583141933D242B0D f25k66k5hu68fneu7ocd 2020-06-16 06:00 logitech.local
52CE2BAFD69B2D0E f2co92njkm9od5eu7btg 2020-06-16 18:30 fc.gov
FACC72E2207CD69F rkspr9a19fl8r5ipggi1 2020-06-17 01:00 fox.local
3256C1BCAF74B5FC p0a7jjdp4eq9o2vok1mt 2020-06-18 07:00 ng.ds.army.mil
92DC5436D54898CD lusq9mg6j1e3jii5f66o 2020-06-18 17:30 ddsn.gov
DB7DE5B93573A3F7 ihvpgv9psvq02ffo77et 2020-06-20 02:30 coxnet.cox.com
59956D687A42F160 o49qi0qbfm37o6jul639 2020-06-23 06:00 wctc.msft
123EDA14721C3602 p5iokg3v9tntqcbo77p2 2020-06-29 08:30 scc.state.va.us
123EDA14721C3602 84v0j8kkbvqf8ntt4o9f 2020-06-30 10:30 scc.state.va.us
2F52CFFCD8993B63 0tvuasje2vc2i2413m6i 2020-07-01 16:30 mgt.srb.europa*
65A28A36F24D379D 7u32o0m6ureci8h5eo6k 2020-07-02 01:00
2F52CFFCD8993B63 en1clufg22h2uca27ro3 2020-07-03 06:00 mgt.srb.europa*
2F52CFFCD8993B63 s2r15kp335mnlq65i6ce 2020-07-03 09:00 mgt.srb.europa*
DB4013DDA16F6A40 up1vj67jjj9tpvceu7ak 2020-07-08 01:00 los.local
123EDA14721C3602 l0vos8o9m5p3m8of7g96 2020-07-10 22:00 scc.state.va.us
E5E2AD2B6DE697D6 8kr7r16da442u75egv1s 2020-07-15 14:00 cisco.com
A13731B17632C726 ttj6cro8jm6cfma8noo7 2020-07-17 12:30 phpds.org
E5E2AD2B6DE697D6 gh1so69rl1sgrgf38gr5 2020-07-17 15:00 cisco.com
E258332529826721 1dbecfd99ku6fi2e5fjb 2020-07-18 05:00
123EDA14721C3602 epm95unblvj984s2ovqh 2020-07-22 11:00 scc.state.va.us
3C327147876E6EA4 k5kcubuassl3alrf7gm3 2020-07-22 17:00 corp.qualys.com
3C327147876E6EA4 mhdosoksaccf9sni9icp 2020-07-23 18:30 corp.qualys.com
F2C9AC93206ABF47 onpqb88oq440lq82p7lb 2020-07-24 05:00 jpso.gov
123EDA14721C3602 0qthjq50jbdvnjq16o8f 2020-07-27 17:00 scc.state.va.us
123EDA14721C3602 gu6r7k260p6afq3ticso 2020-07-28 17:30 scc.state.va.us
936F78AB73AA3022 i4d2krbn2f92jo3uj8r9 2020-08-04 05:00 ggsg-us.cisco.com
936F78AB73AA3022 et2gu9tg5ckrsvaj5bom 2020-08-05 06:00 ggsg-us.cisco.com
22334A7227544B1E 5qbtj04rcbp3tiq8bo6t 2020-09-29 04:00 paloaltonetworks*

SUNBURST STAGE2 Victim Table
Sources: John Bambenek, Joe Słowik, Rohit Bansal, Dancho Danchev , Paul Vixie, FireEye and VriesHd.

Identifying More SUNBURST STAGE2 Victims

Companies and organizations with access to more passive DNS resources will hopefully be able to use SunburstDomainDecoder to identify additional targeted SUNBURST victims that have progressed to STAGE2.

Download SunburstDomainDecoder

Our tool SunburstDomainDecoder is released under a Creative Commons CC-BY license, and can be downloaded here: https://www.netresec.com/files/SunburstDomainDecoder.zip

You can also read more about SunburstDomainDecoder in our blog post Reassembling Victim Domain Fragments from SUNBURST DNS.

Posted by Erik Hjelmvik on Monday, 04 January 2021 21:11:00 (UTC/GMT)

Tags: #Netresec #pDNS #SUNBURST #SolarWinds #Solorigate #SunburstDomainDecoder #SolarStorm #STAGE2 #avsvmcloud #C2

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Reassembling Victim Domain Fragments from SUNBURST DNS

We are releasing a free tool called SunburstDomainDecoder today, which is created in order to help CERT organizations identify victims of the trojanized SolarWinds software update, known as SUNBURST or Solorigate.

SunburstDomainDecoder.exe output showing innout.corp nswhealth.net cisco.com fa.lcl int.lukoil-international.uz tr.technion.ac.il bisco.int phabahamas.org banccentral.com bk.local htwanmgmt.local

SunburstDomainDecoder can be fed with DNS queries to avsvmcloud.com in order to reveal the full internal domain names of infected companies and organizations.

UPDATE December 18, 2020 (v1.1)

SunburstDomainDecoder has now been updated to automatically reassemble fragmented domain name segments in order to show the full domain in the output.

UPDATE December 19, 2020 (v1.2)

Domain names that have been base32 encoded, such as domain names with uppercase letters, can now be extracted with SunburstDomainDecoder. The queried SUNBURST subdomains are now also included in the output.

UPDATE December 21, 2020 (v1.6)

Improved parsing of base32 encoded domain names. SUNBURST victim domains like "LKDataCenter.com", "Sunkistgrowers.com" and "BrokenArrow.Local" can now be extracted.

UPDATE December 27, 2020 (v1.7)

Improved reassembly of long domain names, like "CIMBMY.CIMBDomain.com" and "BE.AJINOMOTO-OMNICHEM.AD", that get segmented into multiple parts. Extraction of time stamps and security applications, including "Windows Defender", "Carbon Black", "CrowdStrike", "FireEye", "ESET" and "F-Secure". See Sergei Shevchenko's blog post Sunburst Backdoor, Part III: DGA & Security Software for more details.

UPDATE January 4, 2021 (v1.8)

Security products (WinDefend, ESET etc.) are now included in the summary output at the end. SUNBURST stage2 victims, which accept C2 domains in CNAME responses, are indicated with a "STAGE2" tag. The previous release marked stage2 queries with a "DNSSEC" tag. Improved extraction of truncated base32 domains, such as "*TED.com".

UPDATE January 12, 2021 (v1.9)

DNS queries with encoded timestamps are tagged with either "AVProducts" or "Ping", depending on if they include an update of the installed/running security products and services or not. The summary data at the end has been modified to also show partial domain names, such as "paloaltonetworks*".

UPDATE February 16, 2021 (v2.0)

Slightly faster and even more accurate than previous versions.

Download SunburstDomainDecoder.zip

 

SUNBURST DNS Traffic

SUNBURST victims, who have installed one of the trojanized SolarWinds Orion software updates, will query for domain names formatted like this:

<SUBDOMAIN>.appsync-api.eu-west-1.avsvmcloud.com <SUBDOMAIN>.appsync-api.us-west-2.avsvmcloud.com <SUBDOMAIN>.appsync-api.us-east-1.avsvmcloud.com <SUBDOMAIN>.appsync-api.us-east-2.avsvmcloud.com

The "SUBDOMAIN" string has different values for each victim and the second half of this string actually contains an encoded domain name (encrypted with a simple substitution cipher).

RedDrip's decode.py

The RedDrip Team published a SUNBURST DGA decoding script yesterday, which can be used to identify SUNBURST victim organizations like CISCO and Belkin by decoding the domain names encoded in the outgoing DNS queries for subdomains of avsvmcloud.com.

This is what it looks like when RedDrip's decode.py script is fed with domain names from John Bambenek's uniq-hostnames.txt file.

cat uniq-hostnames.txt | python decode.py
02m6hcopd17p6h450gt3.appsync-api.us-west-2.avsvmcloud.com .gh
039n5tnndkhrfn5cun0y0sz02hij0b12.appsync-api.us-west-2.avsvmcloud.com ad001.mtk.lo
04spiistorug1jq5o6o0.appsync-api.us-west-2.avsvmcloud.com isi
060mpkprgdk087ebcr1jov0te2h.appsync-api.us-east-1.avsvmcloud.com belkin.com
06o0865eliou4t0btvef0b12eu1.appsync-api.us-east-1.avsvmcloud.com gncu.local
07605jn8l36uranbtvef0b12eu1.appsync-api.us-east-1.avsvmcloud.com gncu.local
07q2aghbohp4bncce6vi0odsovertr2s.appsync-api.us-east-1.avsvmcloud.com csnt.princegeor
07ttndaugjrj4pcbtvef0b12eu1.appsync-api.us-east-1.avsvmcloud.com gncu.local
08amtsejd02kobtb6h07ts2fd0b12eu1.appsync-api.eu-west-1.avsvmcloud.com sm-group.local
0b0fbhp20mdsv4scwo11r0oirssrc2vv.appsync-api.us-east-2.avsvmcloud.com ville.terrebonn
[...]

The beauty of this approach is that passive DNS data can be used in order to reliably identify the victims. This is great news for national CERTs, because they typically have readily access to passive DNS data and can use the decoded domain names in order to identify and reach out to victims in their country.

After using the python script provided by ReadDrip Team I noticed two things:

  1. The leaked domain names were internal domain names used on the victim organizations' corporate networks. Many of the domains were using the ".local" suffix.
  2. Most of the extracted domains were truncated to around 15 bytes, which make it difficult to identify the victim organization.

Truncated Domains Fragmented Domains

I later learned that what seemed to be truncated domains were actually fragmented domains, where long domain names would be split into multiple queries. This revelation turns the output from RedDrip's python tool into an interesting domain name puzzle. At this point I decided to take a closer look at the malicious SolarWinds update I had downloaded from SolarWind's website a few days ago -- yes, that's right the malicious software update "SolarWinds-Core-v2019.4.5220-Hotfix5.msp" (MD5: 02af7cec58b9a5da1c542b5a32151ba1) was actually available for download from SolarWinds' website long after they had been notified about their software being backdoored!

As an example, lets' take a closer look at this DNS query from John Bambenek's passive DNS data: r1qshoj05ji05ac6eoip02jovt6i2v0c.appsync-api.us-west-2.avsvmcloud.com

This query can be broken down into three parts:

  1. r1qshoj05ji05ac6 : What is encoded here???
  2. eoip02jovt6i2v0c : Base32 encoded string "city.kingston."
  3. .appsync-api.us-west-2.avsvmcloud.com : DNS trailer without encoded data

So, which "City of Kingston", or "Kingston City", should we contact to let them know that they have installed a trojanized SolarWinds update? Is it Kingston Jamaica, City of Kingston NY USA, City of Kingston Ontario Canada, Kingston City Tennessee USA or City of Kingston Australia?

After analyzing the "SolarWinds.Orion.Core.BusinessLayer.dll" file (MD5: b91ce2fa41029f6955bff20079468448) from the "SolarWinds-Core-v2019.4.5220-Hotfix5.msp" I learned that the initial "r1qshoj05ji05ac6" string is representing a unique "GUID" value for the infected machine. This GUID is generated by calculating an MD5 hash of the MAC address of the first active non-Loopback network interface, the domain name and the "MachineGuid" registry key value in "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography".

This MD5 hash is then squeezed into a tiny 8 byte array by XOR'ing overlapping bytes. The "CreateSecureString" function in the trojanized SolarWinds update then "encrypts" this hash using XOR with a random key, which is prepended to the data. The XOR key and the XOR'ed data is then finally base32 encoded into what makes up the first part of the subdomain to query for. Don't let the SUNBURST source code below fool you, it is actually using base32 encoding with a custom alphabet even though the function is called "Base64Encode";

CreateSecureString function in SolarWinds.Orion.Core.BusinessLayer.OrionImprovementBusinessLayer.CryptoHelper
Image: SUNBURST source code generates a random value between 1 and 127 as XOR key

Each DNS lookup from an infected machine will query for a unique subdomain because a new XOR key will be generated for each request. Luckily for us, this XOR key is provided in each request, so we can use it in order to "decrypt" the subdomain and get the original 8 bytes derived from the MAC+domain+MachineGuid MD5 hash.

The output from my "SunburstDomainDecoder.exe" tool will print the "decrypted" 8 byte GUID in the first column, the decoded victim domain segment or timestamp in the second column and the queried SUNBURST subdomain in the last column. Each DNS query line read from standard input will generate a "GUID DecodedHostname SunburstSubdomain" line on standard output.

SunburstDomainDecoder.exe < uniq-hostnames.txt
F18613981DEC4D1A 2020-10-02T21:00:00.0000000Z 02m6hcopd17p6h450gt3
BD6DEFBBE9FEA3A9 ad001.mtk.lo 039n5tnndkhrfn5cun0y0sz02hij0b12
2BF8DE15406EA780 2020-08-25T03:00:00.0000000Z 043o9vacvthf0v95t81l
573DEB889FC54130 2020-08-13T21:00:00.0000000Z,​WindowsDefender_RUNNING,CrowdStrike_RUNNING 04jrge684mgk4eq8m8adfg7
518092C8FD571806 2020-06-09T22:30:00.0000000Z 04r0rndp6aom5fq5g6p1
F18613981DEC4D1A 2020-07-06T08:30:00.0000000Z 04spiistorug1jq5o6o0
BC1CB013239B4B92 2020-04-25T10:00:00.0000000Z 05q2sp0v4b5ramdf71l7
3ED2E979D53B2523 belkin.com 060mpkprgdk087ebcr1jov0te2h
4225A5C345C1FC8E gncu.local 06o0865eliou4t0btvef0b12eu1
[...]

The tool then finishes off by outputting the domains that are complete or at least have the last part of their domain intact. Some of these domains are complete because they were short enough to fit in one single SUNBURST DNS query, while others have been pieced together by SunburstDomainDecoder from domain fragments arriving in separate SUNBURST DNS queries.

[...]
F59BBAACBA3493C0 dufferincounty.on.ca
F5D6AA262381B084 glu.com
F9024D5B1E9717C6 gyldendal.local
F90BDDB47E495629 central.pima.gov
F956B5EF56BCF666 coxnet.cox.com
F9A9387F7D252842 city.kingston.on.ca
FB0B50553BC00DED gloucesterva.net
FBB6164BC2B0DFAD ARYZTA.COM
FD04AC52C95A1B0A bmrn.com
FDFCAB8E4C0AB3EE ansc.gob.pe
FE7FF8C9104A0508 thoughtspot.int
FF6760F36DB3D7DC smes.org

We can now see that it was "city.kingston.on.ca", (City of Kingston, Ontario, Canada) who had installed a trojanized SolarWinds update.

Download SunburstDomainDecoder

The C# source code and a compiled Windows binary for SunburstDomainDecoder is available here: https://www.netresec.com/files/SunburstDomainDecoder.zip

Creative Commons CC-BY

The source code and Windows binary is shared under a Creative Commons CC-BY license, which means that you are free to:

  • Share : copy and redistribute the material in any medium or format
  • Adapt : remix, transform, and build upon the material for any purpose, even commercially.
Provided that you give appropriate credit, provide a link to the license, and indicate if changes were made.

Running SunburstDomainDecoder on Linux/MacOS

Wanna run SunburstDomainDecoder.exe but not in Windows? No problems, the tool runs perfectly fine in Mono. Another option is to build SunburstDomainDecoder.cs as a .NET core project in Linux.

.NET Reversing

Would you like to verify my findings or learn more about .NET reverse engineering? Cool, then I'd recommend that you download dnSpy in order to reverse engineer the SUNBURST .NET DLL (which can be extracted from the msp installer with 7zip). Or you can have a look at the already extracted OrionImprovementBusinessLayer.cs on GitHub.

Posted by Erik Hjelmvik on Thursday, 17 December 2020 22:30:00 (UTC/GMT)

Tags: #SunburstDomainDecoder #SUNBURST #SolarWinds #Solorigate #domain #DNS #pDNS #Windows Defender #Carbon Black #FireEye #ESET #F-Secure #Trojan #avsvmcloud

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