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A New Cyber Threat Emerges
A Chinese state-sponsored hacking group, UNC5221, has been actively exploiting a newly discovered critical vulnerability in Ivanti products, according to cybersecurity firm Mandiant. The vulnerability, tracked as CVE-2025-22457, is a buffer overflow flaw that allows attackers to achieve remote code execution (RCE) on targeted systems.
Initially assessed as a low-risk denial-of-service (DoS) vulnerability, further investigation revealed that hackers found a way to exploit it in Ivanti Connect Secure (ICS) version 22.7R2.5 and earlier, elevating its severity to critical. Ivanti released a patch on February 11, 2025, but by mid-March 2025, active exploitation in the wild was already underway.
Security researchers observed the deployment of two newly identified malware families by the group post-exploitation, allowing for persistent access, data exfiltration, and network intrusions. This latest cyber espionage activity underscores China’s ongoing strategy of targeting edge devices—security gateways, VPN appliances, and load balancers—used by critical industries and government organizations.
Post-Compromise Activity: Malware Deployment
Once attackers gained access through CVE-2025-22457, they deployed a variety of memory-resident malware, which remains difficult to detect due to its lack of traditional file-based indicators. Key malware families include:
1. Trailblaze and Brushfire
- Trailblaze: A minimal dropper that injects a passive backdoor named Brushfire
- Brushfire: Hooks into SSL functions, allowing attackers to receive commands without detection
2. Spawn Family Malware
UNC5221 also deployed advanced Spawn-family malware variants:
- Spawnsloth: Modifies logs to evade detection, targeting dslogserver to disable local and remote logging
- Spawnsnare: Encrypts Linux kernel images (vmlinux) using AES encryption, bypassing standard security tools
- Spawnwave: An advanced version of Spawnant, incorporating multiple attack techniques
This post-compromise activity allows attackers to establish persistent access, steal credentials, and launch further network intrusions.
China’s Ongoing Targeting of Edge Devices
UNC5221 has a history of exploiting zero-day vulnerabilities in Ivanti products, NetScaler ADC, and NetScaler Gateway appliances, using them as entry points into government and corporate networks.
China-backed cyber espionage groups have significantly escalated their targeting of edge devices in recent years, focusing on organizations in critical infrastructure, finance, and government sectors. In 2024 alone, several Chinese-affiliated groups extensively exploited Ivanti vulnerabilities to gain unauthorized access to sensitive data.
Mandiant’s CTO, Charles Carmakal, cautioned:
“The latest activity from UNC5221 highlights the growing threat of China-backed espionage groups targeting edge devices worldwide. These groups are improving their custom malware capabilities and speed of attack, making cyber defense increasingly challenging.”
With China’s cyber activities accelerating, businesses and governments must prioritize patching vulnerabilities, enhancing endpoint detection capabilities, and strengthening edge security strategies.
What Undercode Says: Analyzing the UNC5221 Threat
1. Edge Devices: The New Cyber Battleground
UNC5221’s focus on edge devices highlights a shifting cyber warfare strategy. Instead of directly attacking high-security internal systems, hackers compromise perimeter devices, which often lack robust Endpoint Detection and Response (EDR) solutions. This approach allows stealthy, long-term access to networks.
2. Memory-Resident Malware: A Silent Killer
By using memory-resident malware, UNC5221 avoids leaving behind traditional forensic evidence, making it extremely difficult for security teams to detect intrusions. Brushfire’s ability to hook into SSL functions means attackers can maintain covert command-and-control (C2) communications indefinitely.
3. The Growing Sophistication of Chinese Cyber Espionage
China-nexus groups are developing custom malware ecosystems tailored to bypass modern cybersecurity defenses. The Spawn family malware showcases their advanced evasion techniques, particularly in modifying logs and encrypting system components.
4. Patch Delays and Exploit Windows
Despite Ivanti releasing a patch in February 2025, active exploitation was observed by mid-March. This one-month gap suggests many organizations failed to apply patches quickly, leaving them vulnerable. Cybercriminals often weaponize new vulnerabilities within weeks, reinforcing the need for aggressive patch management.
5. UNC5221: A Persistent and Adaptive Threat
UNC5221 has repeatedly demonstrated adaptive exploitation techniques. Even when vulnerabilities are initially classified as low-risk, this group finds innovative ways to achieve remote code execution (RCE). Their ability to reverse-engineer patches and develop exploits rapidly makes them one of the most dangerous state-backed actors today.
6. The Future of Cyber Espionage
Given
Fact Checker Results
- CVE-2025-22457 is confirmed as a critical vulnerability affecting Ivanti Connect Secure (ICS), with an official CVSS score of 9.0.
- UNC5221’s activity aligns with known Chinese cyber espionage tactics, targeting government agencies and enterprise infrastructure.
- Memory-resident malware like Trailblaze and Brushfire has been validated by security researchers as effective at bypassing detection tools.
Final Verdict: The report is highly credible, and organizations should take urgent action to mitigate risks associated with CVE-2025-22457.
References:
Reported By: https://www.infosecurity-magazine.com/news/chinese-state-hackers-ivanti-flaw/
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