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Chinese Hackers Exploited a Maximum-Severity Dell Zero-Day for Nearly Two Years Before Discovery

A hardcoded-credential flaw in Dell RecoverPoint rated CVSS 10.0 let Chinese spies deploy three malware families and hide inside VMware infrastructure since mid-2024.

Cybersecurity Nation-State Threats
cybersecurity zero-day Dell China espionage VMware Mandiant
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Overview

A suspected Chinese state-linked hacking group has been silently exploiting a maximum-severity vulnerability in Dell’s enterprise backup software since at least mid-2024, deploying three distinct malware families and pioneering a stealthy technique for burrowing into VMware virtual infrastructure, according to research published today by Google’s Mandiant threat intelligence team.

The vulnerability, tracked as CVE-2026-22769, carries a perfect CVSS score of 10.0 and affects Dell RecoverPoint for Virtual Machines — a widely used solution for VMware virtual machine backup and disaster recovery. Dell has released a patch and urged organizations to apply it immediately.

The Vulnerability

The flaw is almost comically simple: Dell shipped RecoverPoint with hardcoded default credentials for an Apache Tomcat Manager instance, stored in a plaintext configuration file at /home/kos/tomcat9/tomcat-users.xml. Anyone who knew the credentials could authenticate to the Tomcat Manager, upload a malicious WAR file through the /manager/text/deploy endpoint, and execute commands as root on the appliance, as detailed in Mandiant’s research.

Affected versions include all releases of RecoverPoint for Virtual Machines prior to 6.0.3.1 HF1, according to Dell’s advisory DSA-2026-079.

The Attackers

Mandiant attributes the campaign to a threat cluster it tracks as UNC6201, a suspected People’s Republic of China-nexus group that targets edge appliances — devices like VPN concentrators, firewalls, and backup systems that typically lack endpoint detection and response (EDR) coverage, as reported by The Register.

Researchers note that UNC6201 shares “notable overlaps” with UNC5221, the group behind a series of Ivanti zero-day attacks that targeted government agencies, though the two clusters are not yet considered identical, according to Infosecurity Magazine.

Three Malware Families

Once inside, UNC6201 deployed a layered toolkit of three malware families:

  • SLAYSTYLE — A web shell uploaded through the Tomcat Manager exploit, providing initial command execution on compromised appliances.
  • BRICKSTORM — A more capable backdoor written first in Go and later ported to Rust, designed for persistent access on systems where traditional security tools cannot operate.
  • GRIMBOLT — A novel C# backdoor compiled using native ahead-of-time (AOT) compilation and packed with UPX, making it harder to analyze through static methods. It provides remote shell capability and shares command-and-control infrastructure with BRICKSTORM.

Mandiant observed the attackers replacing BRICKSTORM with GRIMBOLT across compromised environments in September 2025, suggesting an active effort to upgrade their tooling while the campaign remained undetected, according to The Register.

Ghost NICs: Hiding Inside VMware

Perhaps the most technically notable aspect of the campaign is UNC6201’s use of “ghost NICs” — hidden, temporary network interfaces created on virtual machines running on VMware ESXi servers. These phantom network ports allowed the attackers to pivot laterally across victims’ internal networks and into software-as-a-service infrastructure without being visible to standard network monitoring, as detailed in Mandiant’s research.

After completing their operations, the threat actors deleted the ghost NICs, further complicating forensic investigation. The group also employed iptables-based Single Packet Authorization (SPA) to control access to their backdoors, adding another layer of stealth.

Scope and Response

Mandiant confirmed that fewer than a dozen organizations were directly exploited through CVE-2026-22769, though the full scale of the campaign remains unknown. Dell stated it had “received a report of limited active exploitation” and urged “immediate implementation” of the provided remediation steps, according to SecurityWeek.

Dell has published remediation guidance under advisory DSA-2026-079, and has provided YARA detection rules for identifying GRIMBOLT and SLAYSTYLE on affected systems. Organizations running RecoverPoint for Virtual Machines versions prior to 6.0.3.1 HF1 should patch immediately; those still on version 5.3 should follow Dell’s migration guidance.

What We Don’t Know

Several questions remain unanswered. The initial access vector — how UNC6201 first discovered the hardcoded credentials — has not been confirmed. It is also unclear whether the group exploited the flaw opportunistically after discovering it independently or whether the credentials were leaked or shared within China’s broader cyber-espionage ecosystem. The total number of RecoverPoint deployments exposed to the internet, and thus potentially vulnerable, has not been publicly disclosed.