China-linked hackers target government agencies by exploiting flaws in Citrix, Pulse, and F5 systems, and MS Exchange

Pierluigi Paganini September 15, 2020

CISA published an advisory on China-linked groups targeting government agencies by exploiting flaws in Microsoft Exchange, Citrix, Pulse, and F5 systems.

CISA published a security advisory warning of a wave of attacks carried out by China-linked APT groups affiliated with China’s Ministry of State Security.

Chinese state-sponsored hackers have probed US government networks looking for vulnerable networking devices that could be compromised with exploits for recently disclosed vulnerabilities.

“The Cybersecurity and Infrastructure Security Agency (CISA) has consistently observed Chinese Ministry of State Security (MSS)-affiliated cyber threat actors using publicly available information sources and common, well-known tactics, techniques, and procedures (TTPs) to target U.S. Government agencies.” reads the security advisory. “CISA has observed these—and other threat actors with varying degrees of skill—routinely using open-source information to plan and execute cyber operations.”

The list of vulnerabilities targeted by the Chinese hackers are:

  • CVE-2020-5902: F5 Big-IP Vulnerability – CISA has conducted incident response engagements at Federal Government and commercial entities where the threat actors exploited CVE-2020-5902. This is a vulnerability in F5’s Big-IP Traffic Management User Interface that allows cyber threat actors to execute arbitrary system commands, create or delete files, disable services, and/or execute Java code.[7]
  • CVE-2019-19781: Citrix Virtual Private Network (VPN) Appliances – CISA has observed the threat actors attempting to discover vulnerable Citrix VPN Appliances. CVE-2019-19781 enabled the actors to execute directory traversal attacks.[8]
  • CVE-2019-11510: Pulse Secure VPN Servers – CISA has conducted multiple incident response engagements at Federal Government and commercial entities where the threat actors exploited CVE-2019-11510—an arbitrary file reading vulnerability affecting Pulse Secure VPN appliances—to gain access to victim networks. Although Pulse Secure released patches for CVE-2019-11510 in April 2019, CISA observed incidents where compromised Active Directory credentials were used months after the victim organization patched their VPN appliance.[9]
  • CVE-2020-0688: Microsoft Exchange Server – CISA has observed the actors exploiting CVE-2020-0688 for remote code execution to enable email collection of targeted networks.

CISA also warned that the threat actors are exploiting the Microsoft Exchange CVE-2020-0688 RCE vulnerability to access emails from the exchange servers found in Federal Government environments.

According to the advisory, some attacks have been successful and allowed the Chinese hackers to penetrate federal networks.

“According to a recent U.S. Department of Justice indictment, MSS-affiliated actors have targeted various industries across the United States and other countries—including high-tech manufacturing; medical device, civil, and industrial engineering; business, educational, and gaming software; solar energy; pharmaceuticals; and defense—in a campaign that lasted over ten years.[1] continues the advisory. These hackers acted for both their own personal gain and the benefit of the Chinese MSS.[2]”

Once gained a foothold in the target network, Chinese hackers make lateral movements using a variety of tools such as

  • Cobalt Strike: Cobalt Strike is a legitimate adversary simulation platform intended to be used by security professionals to assess a network’s security. Threat actors are using cracked versions as part of their attacks to enable backdoor access to compromised systems and deploy additional tools on the network.
  • China Chopper Web Shell: This tool allows threat actors to install a PHP, ASP, ASPX, JSP, and CFM webshells (backdoor) on publicly exposed web servers. Once the China Chopper Web Shell is installed, the attackers gain full access to a remote server through the exposed web site.
  • Mimikatz: Mimikatz is a post-exploitation tool that allows attackers to dump Windows credentials stored in a computer’s memory.  This tool is commonly used by threat actors, including ransomware operations, utilize to gain access to administrator credentials, and therefore, compromise Windows domain controllers.

CISA recommends that private companies and government agencies adopt necessary countermeasures and patch the devices in their infrastructure:

“CISA and the FBI also recommend that organizations routinely audit their configuration and patch management programs to ensure they can track and mitigate emerging threats. Implementing a rigorous configuration and patch management program will hamper sophisticated cyber threat actors’ operations and protect organizations’ resources and information systems,” states the advisory.

Below the list of patches that could be installed to prevent Chinese hackers and other threat actors from exploiting them:

VulnerabilityPatch Information
CVE-2020-5902F5 Security Advisory: K52145254: TMUI RCE vulnerability CVE-2020-5902
CVE-2019-19781Citrix blog post: firmware updates for Citrix ADC and Citrix Gateway versions 11.1 and 12.0Citrix blog post: security updates for Citrix SD-WAN WANOP release 10.2.6 and 11.0.3Citrix blog post: firmware updates for Citrix ADC and Citrix Gateway versions 12.1 and 13.0Citrix blog post: firmware updates for Citrix ADC and Citrix Gateway version 10.5
CVE-2019-11510Pulse Secure Out-of-Cycle Advisory: Multiple vulnerabilities resolved in Pulse Connect Secure / Pulse Policy Secure 9.0RX
CVE-2020-0688Microsoft Security Advisory: CVE-2020-0688: Microsoft Exchange Validation Key Remote Code Execution Vulnerability
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Pierluigi Paganini

(SecurityAffairs – hacking, China)

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