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National Security and Defense Council of Ukraine
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HomeNewsOrganization of the National Security and Defense Council of Ukraine15.03.2021, 15:15

The NCCC at the NSDC of Ukraine warns of high level of cyber threats due to the exploitation of vulnerabilities in Microsoft Exchange

The National Coordination Center for Cybersecurity at the National Security and Defense Council of Ukraine warns of the active exploitation of vulnerabilities in the widespread software product Microsoft Exchange. If the vulnerabilities are successfully exploited, attackers can execute arbitrary code on vulnerable systems and gain full access to the compromised server, including access to files, e-mail, accounts, etc. Moreover, the successful exploitation of vulnerabilities allows unauthorized access to the resources of the organization’s internal network.

Local versions of Microsoft Exchange Server 2010, Microsoft Exchange Server 2013, Microsoft Exchange Server 2016, Microsoft Exchange Server 2019 are vulnerable. There is no information on vulnerabilities in cloud versions of Microsoft 365, Exchange Online, Azure Cloud.

Vulnerabilities CVE-2021-26855, CVE-2021-26857, CVE-2021-26858, CVE-2021-27065 (common name – ProxyLogon) are currently actively exploited, for vulnerabilities CVE-2021-26412, CVE-2021-26854, CVE- 2021-27078 there are no publicly available exploits.

The greatest activity in exploiting vulnerable systems was demonstrated by the Chinese cyber espionage group Hafnium, but now the activity of other hacker groups has been also confirmed, including Tick (Bronze Butler), LuckyMouse (APT27), Calypso, Websiic, Winnti Group (BARIUM, APT41), Tonto (CactusPete), ShadowPad, Microceen, DLTMiner.

The vulnerability is exploited not only by intelligence groups but also by cybercriminals. The facts of infecting vulnerable systems by ransomware, in particular, new families DearCry, DoejoCrypt have been confirmed. Ransom demanded by the criminals in one of the confirmed cases amounted to over 16 thousand dollars.

Compromised servers are also used to send malware to further infect as many organizations as possible. Several such incidents have already been reported in Ukraine.

It should be noted that usually after compromising the next phases are intelligence (data collection on information systems), and afterwards – information theft. This takes some time, and then in many cases valuable data is encrypted or deleted, and ransom is demanded for them. Such a mechanism for developing cyberattacks poses significant threats of data loss in compromised organizations in the near future – from weeks to months.

Microsoft has released service packs for vulnerable versions and software tools designed to self-test for vulnerabilities (https://github.com/microsoft/CSS-Exchange/tree/main/Security). According to the analysis of update settings and partner notifications, the update procedure does not always automatically provide protection against vulnerabilities for all minor versions of Microsoft Exchange Server. For example, according to the Norwegian parliament, their information systems were hacked and data stolen, although updates had been installed.

Therefore, when installing service packs one should consider the following. The update must be applied from the command line on behalf of a user with administrator privileges, after the installation the server must be restarted. After the update process is complete, the vulnerability must be re-examined (MSERT tool – https://docs.microsoft.com/en-us/windows/security/threat-protection/intelligence/safety-scanner-download or nmap https://github.com/GossiTheDog/scanning/blob/main/http-vuln-exchange.nse script).

Earlier, Microsoft reported unauthorized access to fragments of the source code of its products during a large-scale cyberattack on government agencies and private organizations in the United States, called Solorigate. It is reported that some of the identified vulnerabilities were exploited (as zero-day vulnerabilities) at least 2 months before the release of service packs for Microsoft Exchange Server.

Therefore, the NCCC recommends that vulnerable versions of Microsoft Exchange Server and the networks in which they are used be considered compromised and that incident response procedures be used. If the fact of compromise is not confirmed during the response, it is recommended to strengthen security monitoring measures and monitor the situation, as new data on tactics, techniques and procedures of attackers are received, and indicators of compromise are updated.

As of March 12, 2021, more than 1000 vulnerable Microsoft Exchange Server servers were identified in Ukraine, of which 98,7% are used in the private sector.

The NCCC encourages immediate reporting of compromises or attempts to exploit vulnerabilities at report@ncscc.gov.ua for a coordinated response. The NCCC experts are ready to provide technical and advisory assistance in responding, in particular, to private sector organizations.

The geographical distribution of vulnerable servers is shown in the figure.

Technical data

The CISA (US) agency recommends searching for signs of compromise at least from January 1, 2021.

You can check for signs of compromise by running the script (Microsoft) Test-ProxyLogon.ps1 (https://github.com/microsoft/CSS-Exchange/tree/main/Security)

During the exploitation of vulnerabilities in the compromised system, a so-called web shell – a script designed for remote access and management (administration) of an infected system. Typically, a web shell is used to steal credentials, download other malicious code (for example, to search for other victims and infect them), as a command server to manage other infected systems.

Volexity has analyzed the exploitation of Microsoft Exchange Server vulnerabilities. According to the analysis:

HTTP POST requests are made to the following files:

      /owa/auth/Current/themes/resources/logon.css

     /owa/auth/Current/themes/resources/owafont_ja.css

     /owa/auth/Current/themes/resources/lgnbotl.gif

     /owa/auth/Current/themes/resources/owafont_ko.css

     /owa/auth/Current/themes/resources/SegoeUI-SemiBold.eot

     /owa/auth/Current/themes/resources/SegoeUI-SemiLight.ttf

     /owa/auth/Current/themes/resources/lgnbotl.gif

ESR server log files in \Logging\ECP\Server\ contain the following or similar strings:

 S:CMD=Set-OabVirtualDirectory.ExternalUrl='

The presence of files in the following directories indicates an active web shell:

\inetpub\wwwroot\aspnet_client\ (any.aspx file in this directory or in subdirectories)

\\FrontEnd\HttpProxy\ecp\auth\ (any.aspx file except TimeoutLogoff.aspx)

 \\FrontEnd\HttpProxy\owa\auth\ (any file or modified file that is not part of the standard installation)

 \\FrontEnd\HttpProxy\owa\auth\Current\ (any.aspx file in this directory or in subdirectories)

 \\FrontEnd\HttpProxy\owa\auth\\ (any.aspx file in this directory or in subdirectories)

A directory search by /owa/ auth/Current contains the following user-agent strings:

DuckDuckBot/1.0;+(+http://duckduckgo.com/duckduckbot.html)

facebookexternalhit/1.1+(+http://www.facebook.com/externalhit_uatext.php)

Mozilla/5.0+(compatible;+Baiduspider/2.0;++http://www.baidu.com/search/spider.html)

Mozilla/5.0+(compatible;+Bingbot/2.0;++http://www.bing.com/bingbot.htm)

Mozilla/5.0+(compatible;+Googlebot/2.1;++http://www.google.com/bot.html

Mozilla/5.0+(compatible;+Konqueror/3.5;+Linux)+KHTML/3.5.5+(like+Gecko)+(Exabot-Thumbnails)

Mozilla/5.0+(compatible;+Yahoo!+Slurp;+http://help.yahoo.com/help/us/ysearch/slurp)

Mozilla/5.0+(compatible;+YandexBot/3.0;++http://yandex.com/bots)

Mozilla/5.0+(X11;+Linux+x86_64)+AppleWebKit/537.36+(KHTML,+like+Gecko)+Chrome/51.0.2704.103+Safari/537.36

The above user-agent stings are not mandatory indicators of compromise, but should be investigated further.

Such user-agent strings were observed during the exploit from URL /ecp/:

     ExchangeServicesClient/0.0.0.0

     python-requests/2.19.1

     python-requests/2.25.1

Such user-agent strings were observed after the exploit when accessing the web shell:

     antSword/v2.1

     Googlebot/2.1+(+http://www.googlebot.com/bot.html)

Mozilla/5.0+(compatible;+Baiduspider/2.0;++http://www.baidu.com/search/spider.html)

If you find non-standard user-agent strings, you must examine the IIS logs on the Exchange server to analyze their activity. The following requests are not mandatory indicators of compromise:

     POST /owa/auth/Current/

     POST /ecp/default.flt

     POST /ecp/main.css

     POST /ecp/.js

According to Microsoft, there was a web shell in the following directories:

     \inetpub\wwwroot\aspnet_client\

     \inetpub\wwwroot\aspnet_client\system_web\

     %PROGRAMFILES%\Microsoft\Exchange Server\V15\FrontEnd\HttpProxy\owa\auth\

     \Exchange\FrontEnd\HttpProxy\owa\auth\

File names of detected web shells:

web.aspx, help.aspx, document.aspx, errorEE.aspx, errorEEE.aspx, errorEW.aspx, errorFF.aspx,  healthcheck.aspx, aspnet_www.aspx, aspnet_client.aspx, xx.aspx, shell.aspx, aspnet_iisstart.aspx,  one.aspx

Додатковими індикаторами компрометації можуть бути наявність нестандартних підозрілих архівів .zip, .rar, .7z в каталозі C:\ProgramData\, що може свідчити про витік інформації, та дампів процесу LSASS в каталогах C:\windows\temp\, C:\root\.

Additional indicators of compromise may be the presence of non-standard suspicious archives .zip, .rar, .7z in the directory C:\ ProgramData\, which may indicate a leak, and dumps of the LSASS process in the directories C:\windows\temp\, C:\ root\.

Available indicators

File name

File size

Hash sum SHA2

zXkZu6bn.aspx

2287

71ff78f43c60a61566dac1a923557670e5e832c4adfe5efb91cac7d8386b70e0

shell.aspx

2287

ee883200fb1c58d22e6c642808d651103ae09c1cea270ab0dc4ed7761cb87368

RedirSuiteServerProxy.aspx

3349

c8a7b5ffcf23c7a334bb093dda19635ec06ca81f6196325bb2d811716c90f3c5

discover.aspx

2230

1e0803ffc283dd04279bf3351b92614325e643564ed5b4004985eb0486bf44ee

F48zhi6U.aspx

2211

d9c75da893975415663c4f334d2ad292e6001116d829863ab572c311e7edea77

discover.aspx

2204

c0caa9be0c1d825a8af029cc07207f2e2887fce4637a3d8498692d37a52b4014

Fc1b3WDP.aspx

2230

be17c38d0231ad593662f3b2c664b203e5de9446e858b7374864430e15fbf22d

UwSPMsFi.aspx

2168

d637b9a4477778a2e32a22027a86d783e1511e999993aad7dca9b7b1b62250b8

2XJHwN19.aspx

2177

31a750f8dbdd5bd608cfec4218ccb5a3842821f7d03d0cff9128ad00a691f4bd

E3MsTjP8.aspx

2353

bda1b5b349bfc15b20c3c9cbfabd7ae8473cee8d000045f78ca379a629d97a61

web.config.aspx

2241

5ac7dec465b3a532d401afe83f40d336ffc599643501a40d95aa886c436bfc0f

0q1iS7mn.aspx

2267

138f0a63c9a69b35195c49189837e899433b451f98ff72c515133d396d515659

McYhCzdb.aspx

2264

0c5fd2b5d1bfe5ffca2784541c9ce2ad3d22a9cb64d941a8439ec1b2a411f7f8

8aUco9ZK.aspx

2267

36149efb63a0100f4fb042ad179945aab1939bcbf8b337ab08b62083c38642ac

ogu7zFil.aspx

2284

508ac97ea751daebe8a99fa915144036369fc9e831697731bf57c07f32db01e8

 

 

b75f163ca9b9240bf4b37ad92bc7556b40a17e27c2b8ed5c8991385fe07d17d0

 

 

097549cf7d0f76f0d99edf8b2d91c60977fd6a96e4b8c3c94b0b1733dc026d3e

 

 

2b6f1ebb2208e93ade4a6424555d6a8341fd6d9f60c25e44afe11008f5c1aad1

 

 

65149e036fff06026d80ac9ad4d156332822dc93142cf1a122b1841ec8de34b5

 

 

511df0e2df9bfa5521b588cc4bb5f8c5a321801b803394ebc493db1ef3c78fa1

 

 

4edc7770464a14f54d17f36dc9d0fe854f68b346b27b35a6f5839adf1f13f8ea

 

 

811157f9c7003ba8d17b45eb3cf09bef2cecd2701cedb675274949296a6a183d

 

 

1631a90eb5395c4e19c7dbcbf611bbe6444ff312eb7937e286e4637cb9e72944

 

ІР addresses

    103.77.192.219

    104.140.114.110

    104.250.191.110

    108.61.246.56

    149.28.14.163

    157.230.221.198

    167.99.168.251

    185.250.151.72

    192.81.208.169

    203.160.69.66

    211.56.98.146

    5.254.43.18

    5.2.69.14

    80.92.205.81

    91.192.103.43

Download in STIX format https://us-cert.cisa.gov/sites/default/files/publications/AA21-062A.stix.xml 

 

 

 

Malicious activities by the MITRE ATT&CK® classification