When Patching Isn’t Enough

When Patching Isn’t Enough

While patching is one of cybersecurity’s best practices, in some cases, this best practice isn’t enough to protect your organization’s network. Such is the case of patching your organization’s Pulse Secure VPN product.

Pulse Secure VPN Patch

On April 24, 2019, VPN vendor Pulse Secure released software updates, also known as patches, addressing multiple security vulnerabilities, including a patch for the security vulnerability designated as CVE-2019-11510. This security vulnerability allows an unauthenticated remote attacker with network access via HTTPS to send a specially crafted URI to perform an arbitrary file reading vulnerability.

Because of the CVE-2019-11510 vulnerability, an attacker will then be able to view files, such as plain text cache of credentials of past VPN users. Armed with stolen credentials, an attacker can pretend to be a legitimate Pulse Secure VPN user. The following are the affected Pulse Secure VPN versions:

• Pulse Connect Secure 9.0R1 - 9.0R3.3
• Pulse Connect Secure 8.3R1 - 8.3R7
• Pulse Connect Secure 8.2R1 - 8.2R12
• Pulse Connect Secure 8.1R1 - 8.1R15
• Pulse Policy Secure 9.0R1 - 9.0R3.1
• Pulse Policy Secure 5.4R1 - 5.4R7
• Pulse Policy Secure 5.3R1 - 5.3R12
• Pulse Policy Secure 5.2R1 - 5.2R12
• Pulse Policy Secure 5.1R1 - 5.1R15

Following the release of Pulse Secure security updates, Cyber Security Centers in several countries, including Canada, US and Japan have issued alerts calling local organizations to apply in a timely manner the security updates released by Pulse Secure, including the patch for CVE-2019-11510.

Post Pulse Secure VPN Patching Exploitation

The United States’ Cybersecurity and Infrastructure Security Agency (CISA) recently issued a follow-up alert, warning organizations that those that applied the April 24, 2019 Pulse Secure VPN update could still face continued threat actor exploitation post Pulse Secure VPN patching. According to CISA, as the security vulnerability CVE-2019-11510 allows attackers to steal victim organizations’ credentials, failing to change those stolen credentials allows an attacker to move laterally through the organization’s network even after the organization has patched this vulnerability.

CISA reported it observed threat actors used connection proxies, such as Tor infrastructure and virtual private servers (VPSs), to lessen the chance of detection when they connected to victims’ networks via Pulse Secure VPN. The US Cybersecurity Agency found that once inside the victims’ networks, threat actors conducted the following malicious activities:

• Creating persistence via scheduled tasks/remote access trojans
• Amassing files for exfiltration
• Executing ransomware on the victim’s network environment

CISA added that, in one case, it observed a malicious actor attempting to sell the stolen Pulse Secure VPN credentials after 30 unsuccessful attempts to connect to a victim’s network to escalate privileges and drop ransomware. CISA also noted that this same malicious actor successfully dropped ransomware at hospitals and U.S. Government entities.

CISA further reported that malicious actors that leveraged stolen Pulse Secure VPN credentials used tools such as LogMeIn and TeamViewer. LogMeIn is a software that allows users to remotely access another computer. TeamViewer, meanwhile, is an all-in-one solution for remote support, remote access and online meetings. According to CISA, LogMeIn and TeamViewer enable malicious actors to maintain access to the victim’s network environment if they lost their primary connection, that is, via VPN access.

Preventive and Mitigating Measures Against Post Pulse Secure VPN Patching Exploitation

As many organizations encourage employees to work from home as a result of the current COVID-19 crisis, the use of VPN products has been increasing. It’s important to secure this communication line between remote workers and your organization.

Patching, from the word “patch”, is a set of changes to the source code of a software program for the purpose of fixing a known security vulnerability or to improve it.

While patching is still one of the top cybersecurity best practices, this practice alone isn’t enough especially when the exploited security vulnerability involves stolen authentication credentials. According to the US Cybersecurity Agency, organizations that have applied patches for CVE-2019-11510 may still be at risk for exploitation from compromises that occurred pre-patch.

Below are the suggested detection methods by the US Cybersecurity Agency to find out if your organization had been targeted before applying the Pulse Secure VPN patch.

• Turn on unauthenticated log requests.
• Check logs for exploit attempts. To detect exploit attempts, look in the logs for strings such as ../../../data.
• Manually review logs for unauthorized sessions, in particular, sessions originating from unexpected geo-locations.
• Run CISA’s detection tool – a tool that’s available on CISA’s GitHub page. This tool allows system administrators to triage logs (provided authenticated request logging is turned on) and automatically search for CVE-2019-11510 exploitation.

The following are the additional suggested mitigating measures against post Pulse Secure VPN patching exploitation:

• Look for software programs installed without authorization.
• Remove software programs, especially those that allow remote access not approved by your organization.
• Remove any remote access trojans – malicious software that disguised as legitimate software.
• Check scheduled tasks for scripts or executables that could allow an attacker to connect to your organization’s work stations or servers.

“If organizations find evidence of malicious, suspicious, or anomalous activity or files, they should consider reimaging the workstation or server and redeploying back into the environment,” the US Cybersecurity Agency said.