NHS Warns of Hackers Targeting Log4j Flaws in VMware Horizon

The digital security team at the U.K. National Health Service
(NHS) has raised the alarm on active exploitation of Log4Shell
vulnerabilities in unpatched VMware Horizon^[1]
servers by an unknown threat actor to drop malicious web shells and
establish persistence on affected networks for follow-on
attacks.

“The attack likely consists of a reconnaissance phase, where the
attacker uses the Java Naming and Directory InterfaceTM (JNDI) via
Log4Shell payloads to call back to malicious infrastructure,” the
non-departmental public body said^[2]
in an alert. “Once a weakness has been identified, the attack then
uses the Lightweight Directory Access Protocol (LDAP) to retrieve
and execute a malicious Java class file that injects a web shell
into the VM Blast Secure Gateway service.”

The web shell, once deployed, can serve as a conduit to carry
out a multitude of post-exploitation activities such as deploying
additional malicious software, data exfiltration, or deployment of
ransomware. VMware Horizon versions 7.x and 8.x are vulnerable to
the Log4j vulnerabilities.

Log4Shell^[3]
is an exploit for CVE-2021-44228 (CVSS score: 10.0), a critical
arbitrary remote code execution flaw in Apache Log4j 2, an
ubiquitous open-source logging framework, which has been put to use
as part of different malware campaigns^[4] since it came to light
in December 2021. An array of hacking groups, ranging from
nation-state actors to ransomware cartels, have pounced on the
vulnerability to date.

The development also marks the second time VMware products have
come under exploitation stemming as a result of vulnerabilities in
the Log4j library. Last month, AdvIntel researchers disclosed^[5]
that attackers were targeting systems running VMware VCenter
servers with the aim of installing Conti ransomware.

VMware, for its part, has already released security updates^[6] for Horizon, VCenter,
and other products last month that have been impacted by Log4Shell,
with the virtualization services provider acknowledging scanning
attempts in the wild, urging customers to install the patches where
applicable or apply workarounds temporarily to counter any
potential risk.