Play Ransomware Exploits Windows Flaw

Summary

Play ransomware exploited a Windows zero-day vulnerability, escalating privileges and deploying malware. This sophisticated attack targeted various sectors globally, highlighting the growing need for robust cybersecurity measures. The vulnerability, CVE-2025-29824, was patched in April 2025, but not before impacting numerous organizations.

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** Main Story**

The Play ransomware group, also known as PlayCrypt and Balloonfly, exploited a zero-day vulnerability (CVE-2025-29824) in the Windows Common Log File System (CLFS) driver. This vulnerability allowed attackers to escalate privileges to the SYSTEM level, effectively granting them complete control over compromised systems. While Microsoft patched the vulnerability in April 2025, the Play ransomware group and other threat actors, such as RansomEXX, exploited it before the patch was released.

Play Ransomware’s Global Impact

The Play ransomware group launched attacks across various sectors worldwide, impacting IT and real estate organizations in the U.S., the financial sector in Venezuela, a Spanish software company, and the retail sector in Saudi Arabia. The attackers commonly used the Grixba infostealer to gather information about users and computers within compromised networks. Evidence suggests that a public-facing Cisco ASA firewall may have been the initial infection vector in some attacks. After gaining access, attackers moved laterally within the network, deploying the CVE-2025-29824 exploit to escalate privileges, and then deploying malware like the Grixba infostealer. In some instances, the attackers disguised malware files as Palo Alto Networks software within the Music folder to avoid detection.

Technical Details of the Exploit

The attackers exploited the CLFS driver vulnerability by creating two key files: PDUDrv.blf and clssrv.inf. PDUDrv.blf is a CLFS log artifact, while clssrv.inf is a malicious DLL file injected into the winlogon.exe process. This malicious DLL then drops two batch files: servtask.bat and cmdpostfix.bat. Servtask.bat escalates privileges, dumps sensitive Registry hives, creates a new administrative user named “LocalSvc,” and adds it to the Administrator group. Cmdpostfix.bat then removes traces of the intrusion in an attempt to cover their tracks.

Increasing Sophistication of Ransomware Attacks

The exploitation of a zero-day vulnerability by a ransomware group like Play underscores a concerning trend in the cybercrime landscape. Traditionally, zero-day exploits were primarily associated with nation-state actors, but increasingly, sophisticated cybercriminal groups are using them. This indicates that ransomware operators are investing their illicit profits into developing custom tools, faster encryption routines, and stealthier data exfiltration techniques. The Play ransomware group, active since at least June 2022, is known for its double-extortion tactics, where they not only encrypt victims’ data but also steal it and threaten to leak it online if a ransom is not paid. The FBI, CISA, and the Australian Cyber Security Centre issued a joint advisory in December 2023, warning that the Play ransomware gang had already breached around 300 organizations worldwide by October 2023. Previous victims of Play ransomware include high-profile organizations such as Rackspace, Arnold Clark, the City of Oakland, Dallas County, the Belgian city of Antwerp, Microchip Technology, and Krispy Kreme.

Protecting Against Zero-Day Exploits

While the specific attack vector used by the Play ransomware group has been patched, the incident serves as a crucial reminder of the importance of proactive cybersecurity measures. Organizations must adopt a multi-layered security approach, including:

• Regular Patching: Implement robust patch management processes to ensure that all software, including operating systems and applications, are up-to-date with the latest security patches. Timely patching is crucial to mitigate the risk of zero-day exploits.
• Zero Trust Security: Implement a Zero Trust security model that assumes no implicit trust and requires verification for every user and device attempting to access network resources. This helps to limit the impact of a successful breach by restricting lateral movement within the network.
• Network Segmentation: Segment the network into smaller, isolated zones to contain the spread of malware and limit the blast radius of an attack. This prevents attackers from easily moving laterally across the network after gaining initial access.
• Intrusion Detection and Prevention Systems: Deploy intrusion detection and prevention systems (IDPS) to monitor network traffic for malicious activity and automatically block or alert on suspicious events.
• Security Awareness Training: Educate employees about cybersecurity best practices, such as recognizing and avoiding phishing emails, which are a common initial infection vector for ransomware attacks.
• Regular Backups: Maintain regular backups of critical data and systems, stored offline or in an air-gapped environment, to ensure business continuity in the event of a ransomware attack. This allows organizations to restore their systems without having to pay a ransom.
• Incident Response Plan: Develop and regularly test an incident response plan to ensure a coordinated and effective response in the event of a security incident. This plan should include procedures for containment, eradication, and recovery.

By implementing these proactive security measures, organizations can significantly reduce their risk of falling victim to ransomware attacks and other cyber threats.