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Continued Threat Actor Exploitation Post Pulse Secure VPN Patching

This Alert provides an update to Cybersecurity and Infrastructure Security Agency (CISA) Alert AA20-010A: Continued Exploitation of Pulse Secure VPN Vulnerability, which advised organizations to immediately patch CVE-2019-11510—an arbitrary file reading vulnerability affecting Pulse Secure virtual private network (VPN) appliances.[1] CISA is providing this update to alert administrators that threat actors who successfully exploited CVE-2019-11510 and stole a victim organization’s credentials will still be able to access—and move laterally through—that organization’s network after the organization has patched this vulnerability if the organization did not change those stolen credentials.

This Alert provides new detection methods for this activity, including a CISA-developed tool that helps network administrators search for indicators of compromise (IOCs) associated with exploitation of CVE-2019-11510. This Alert also provides mitigations for victim organizations to recover from attacks resulting from CVE-2019-11510. CISA encourages network administrators to remain aware of the ramifications of exploitation of CVE-2019-11510 and to apply the detection measures and mitigations provided in this report to secure networks against these attacks.

For a downloadable copy of IOCs, see STIX file.

Background

CISA has conducted multiple incident response engagements at U.S. Government and commercial entities where malicious cyber threat actors have 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,[2] CISA has observed incidents where compromised Active Directory credentials were used months after the victim organization patched their VPN appliance.

Technical Details

CISA determined that cyber threat actors have been able to obtain plaintext Active Directory credentials after gaining Initial Access [TA0001] to a victim organization’s network via VPN appliances. Cyber threat actors used these Valid Accounts [T1078] in conjunction with:

  • External Remote Services [T1133] for access,
  • Remote Services [T1021] for Lateral Movement [TA0008] to move quickly throughout victim network environments, and
  • Data Encrypted for Impact [T1486 ] for impact, as well as
  • Exfiltration [TA0010] and sale of the data.

Initial Access

CVE-2019-11510 is a pre-authentication arbitrary file read vulnerability affecting Pulse Secure VPN appliances. A remote attacker can exploit this vulnerability to request arbitrary files from a VPN server. The vulnerability occurs because directory traversal is hard coded to be allowed if the path contains dana/html5/acc.[3],[4] For example, a malicious cyber actor can obtain the contents of /etc/passwd [5] by requesting the following uniform resource identifier (URI):

https://vulnvpn.example[.]com/dana-na/../dana/html5/acc/guacamole/../../../../../../../etc/passwd?/dana/html5acc/guacamole/

Obtaining the contents of /etc/passwd gives the attacker access to basic information about local system accounts. This request was seen in the proof of concept (POC) code for this exploit on Github. An attacker can also leverage the vulnerability to access other files that are useful for remote exploitation. By requesting the data.mdb object, an attacker can leak plaintext credentials of enterprise users.[6],[7],[8]

Open-source reporting indicates that cyber threat actors can exploit CVE-2019-11510 to retrieve encrypted passwords;[9] however, CISA has not observed this behavior. By reviewing victim VPN appliance logs, CISA has noted cyber threat actors crafting requests that request files that allow for Credential Dumping [T1003] plaintext passwords from the VPN appliance.

Read more at CISA

Homeland Security Todayhttp://www.hstoday.us
The Government Technology & Services Coalition's Homeland Security Today (HSToday) is the premier news and information resource for the homeland security community, dedicated to elevating the discussions and insights that can support a safe and secure nation. A non-profit magazine and media platform, HSToday provides readers with the whole story, placing facts and comments in context to inform debate and drive realistic solutions to some of the nation’s most vexing security challenges.

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