Malware Analysis Report (AR21-202D)

MAR-10334057-2.v1: Pulse Connect Secure

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Summary

Malware Analysis Report
10334057.r2.v1
2021-07-14

Notification

This report is provided "as is" for informational purposes only. The Department of Homeland Security (DHS) does not provide any warranties of any kind regarding any information contained herein. The DHS does not endorse any commercial product or service referenced in this bulletin or otherwise.

This document is marked TLP:WHITE--Disclosure is not limited. Sources may use TLP:WHITE when information carries minimal or no foreseeable risk of misuse, in accordance with applicable rules and procedures for public release. Subject to standard copyright rules, TLP:WHITE information may be distributed without restriction. For more information on the Traffic Light Protocol (TLP), see http://www.cisa.gov/tlp.

Summary

Description

CISA received two (2) files for analysis. The files are Pulse Secure Common Gateway Interface (CGI) scripts that have been modified. The primary purpose of these system modifications is to provide a remote operator Command and Control (C2) access over a compromised device running the modified scripts. This analysis is derived from malicious files found on Pulse Connect Secure devices.

For a downloadable copy of IOCs, see: MAR-10334057-2.v1.WHITE.stix.

Submitted Files (2)

55800aa55e96ed160dcef2dcc0797085c2d6c9f70b522eed3d269e2f3268014e (tnchcupdate.cgi)

814b430126795b4b06c0b5c3c4919c7a55be441f45756282b0754e3517141f93 (healthcheck.cgi)

Findings

814b430126795b4b06c0b5c3c4919c7a55be441f45756282b0754e3517141f93

Tags

webshell

Details
Name healthcheck.cgi
Size 9272 bytes
Type Perl script text executable
MD5 b817140c6e511e1a6254c19aa855c0b4
SHA1 c8280f0b4391087327138cf14886e6fe48ed102a
SHA256 814b430126795b4b06c0b5c3c4919c7a55be441f45756282b0754e3517141f93
SHA512 485b7346261f74113a7809e6a010bc4baf1a2dc09fc03df64b36144c02a255e5cfd2bbc3458de15b3551213a690c090f83c06065cca6910e4995ceef3c86d2b1
ssdeep 192:XzwJNuIYj7rcCOk1QrhMeWyOUV9AWojcZiOQiQsfinnoK9Cih1pa+7yiPhm:XzwJwrXWOUV9AWojoiOubQ
Entropy 5.116529
Antivirus
Symantec Hacktool.Webshell
YARA Rules

No matches found.

ssdeep Matches
97 85f74424fb4c7dba9f2e9c60a95c8a226a97f7dfc277f5ce6f34862a9f500226
97 c445cab266549820d54168cb8e5078811d574682edce7edb973b3d833128f4e3
Description

This file is a Pulse Secure CGI script with malicious code patched to the end of the file (Figure 1, 2 and 3).

If the system receives a POST request that match any one of the following three conditions it will trigger the malicious code. Otherwise, it defaults to the original Pulse Secure application.

Condition 1: The attacker submits a RC4 encrypted and base64 encoded shell command under the 'cert' parameter. The command is base64 decoded and RC4 decrypted before it is executed. The command's output is sent to the attacker.


Condition 2: The attacker provides input to two parameters: 'img' and 'name', then it calls the function (sub c), which only processes input to the 'img' parameter. The input is base64 decoded and RC4 decrypted, then it is written to a file named tmp. The file is then RC4 encrypted and base64 encoded before being sent to the attacker.

Condition 3: The attacker submits RC4 encrypted and base64 encoded shell commands under the 'name' parameter, leaving the parameter 'img' blank. The shell command is base64 decoded and RC4 decrypted before it is executed, the command output is RC4 encrypted and base64 encoded before sending to the attacker.

The following functions describe the encryption scheme employed by the malware (Figure 1).

sub r: This function generates random bytes to be used in (sub a) for encryption.

sub a: First it calls the (sub r) function to obtain a random six bytes ($k), which is prepended to the hard coded passphrase ($ph) and forms the RC4 encryption key to encrypt the string ($st). The encrypted string is then base64 encoded.

sub b: First, it base64 decodes the input string. The decoded string ($s) is separated into the first six bytes ($k) and the rest without the first six bytes ($en). The first six bytes ($k) is prepended to the hard coded passphrase ($ph) and forms the RC4 decryption key ($k.$ph) to decrypt the string ($en).

Screenshots
Figure 1 - Screenshot of the patched in malicious code at the end of healthcheck.cgi. This section contains the encryption scheme employed by the malware.

Figure 1 - Screenshot of the patched in malicious code at the end of healthcheck.cgi. This section contains the encryption scheme employed by the malware.

Figure 2 - Screenshot of the patched in malicious code at the end of healthcheck.cgi, continued from Figure 1. This screenshot contains function (sub c) which is called under condition 2 and function (sub d) which is called under condition 1.

Figure 2 - Screenshot of the patched in malicious code at the end of healthcheck.cgi, continued from Figure 1. This screenshot contains function (sub c) which is called under condition 2 and function (sub d) which is called under condition 1.

Figure 3 - Screenshot of the patched in malicious code at the end of healthcheck.cgi, continued from Figure 1. This screenshot contains function (sub e) which is called under condition 3 and the function (sub f) which decides the execution of functions (sub c, d and e) depending on the input parameters.

Figure 3 - Screenshot of the patched in malicious code at the end of healthcheck.cgi, continued from Figure 1. This screenshot contains function (sub e) which is called under condition 3 and the function (sub f) which decides the execution of functions (sub c, d and e) depending on the input parameters.

55800aa55e96ed160dcef2dcc0797085c2d6c9f70b522eed3d269e2f3268014e

Tags

webshell

Details
Name tnchcupdate.cgi
Size 27958 bytes
Type Perl script text executable
MD5 b0106374ad72e0e63c73d4013cd1284a
SHA1 d864f76565f48a545c5ac8067a65a761402faad5
SHA256 55800aa55e96ed160dcef2dcc0797085c2d6c9f70b522eed3d269e2f3268014e
SHA512 7a4e4430d87f7178a3c302d8d4fc0cb63683858ca04de6d4da739bfa1839c85e8d6681d1646705b11dc1e94f1e3543d4779d35c968079cac0b293b90b3fa6019
ssdeep 384:X/XaWMIVzjJVreteR03LD/AxrYjVRzptulRvU71F2K9gjOTU:X/Xa94jJVrete2gxrYj34vU7/2K2CU
Entropy 4.919695
Antivirus

No matches found.

YARA Rules

No matches found.

ssdeep Matches
99 779d5410b6974cacacfdcddd68e7dac2409ea7957b9be4ae049466bd550de63c
99 c964594ed0afaf64611514eb53f14ee5ab95e25da986dca9e28586bfc053da16
Description

This file is a modified version of a Pulse Secure Perl CGI file (Figure 4). It is designed to perform an initial check to determine whether data was passed into the web application within a parameter named "id". If this parameter is provided, the code will extract its contents and execute them on the target system using the system() function. If no "id" parameter is passed to the application, the code will simply execute the main() function of the original Pulse Secure application.

Screenshots
Figure 4 - Screenshot of the malicious code patched-in to the end-of-file.

Figure 4 - Screenshot of the malicious code patched-in to the end-of-file.

Recommendations

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".

Contact Information

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/

Document FAQ

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.

Revisions

July 21, 2021: Initial Version

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