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Highlights:
- CVE-2025-29824 is a critical Windows zero-day vulnerability exploited to gain SYSTEM-level access.
- The Storm-2460 group used this flaw to deploy ransomware across various sectors globally.
- Microsoft released patches for Windows Server and Windows 11; Windows 10 updates were delayed.
- Organizations should apply patches, monitor system activity, and implement advanced security measures to protect against such threats.
In April 2025, Microsoft patched a critical zero‑day vulnerability, CVE‑2025‑29824, in the Common Log File System (CLFS) driver (clfs.sys) used by Windows, which allowed local privilege escalation. CVSS v3.1 assigns it a high severity score of 7.8, enabling any authorized local user to elevate to SYSTEM privileges without requiring user interaction. Sophisticated adversaries exploited this use-after-free weakness (CWE‑416) in real-world attacks, triggering urgent action from Microsoft and cybersecurity teams.
Discovery, Impact & Targets of Exploitation
According to Microsoft’s Threat Intelligence Center and Security Response Center, a threat organization called Storm-2460 was found to be actively exploiting this CLFS vulnerability. This group executed the zero-day in memory and elevated privileges on compromised systems using a custom loader called PipeMagic.
Targets affected included Saudi Arabian retail companies, financial institutions in Venezuela, a Spanish software company, and companies in the U.S. real estate and IT sectors. Separately, before the official patch, attackers associated with the Play (Balloonfly) ransomware family also exploited CVE-2025-29824. Symantec discovered that the exploit was deployed in folders posing as Palo Alto Network tools (such as “paloaltoconfig.exe”) in attacks against U.S.-based companies.
Technical Anatomy
At its core, CVE‑2025‑29824 abuses a use‑after‑free bug in the CLFS driver by manipulating two threads to orchestrate a race condition.
This engineering allowed attackers to elevate privileges, execute credential dumps (via LSASS), expand lateral movement, tamper with logs, delete backups, and lay groundwork for potential ransomware, especially in the Storm‑2460 attacks, where full encryption later followed.
Attack Chain & Ransomware Deployment
Usually, a first breach utilizing commodity malware (unrelated to the zero-day) preceded the complete attack development. According to Microsoft investigations, actors used certutil to drop malicious MSBuild projects, which then used the EnumCalendarInfoA API to decode and run PipeMagic, a sophisticated loader. The successful exploitation of CLFS made it possible to escalate to SYSTEM, execute payloads, and get ready to disseminate ransomware.
In the end, ransomware was used in Storm-2460 instances. Custom ransom notes directing to onion domains in the RansomEXX style, extensive log cleanup, and registry changes to turn off recovery capabilities were all signs of compromise.
Ransomware assaults used the same CLFS vulnerability for local exploitation, but they didn’t necessarily spread ransomware. Instead, they used PowerShell to do reconnaissance across Active Directory and launch the information-stealing program Grixba.
Microsoft’s Patch & Affected Platforms
Microsoft addressed CVE‑2025‑29824 in its Patch Tuesday release on April 8, 2025, covering a variety of Windows versions: Windows 10 (pre‑21H2 builds), plus Server 2008, 2012, and 2012 R2. The advisory highlights that Windows 11 version 24H2 and newer are unaffected by the exploit mechanism, even if the vulnerability exists. Updates were delayed for some Windows 10 SKUs; pending patches were scheduled promptly afterward .
CISA recognized CVE‑2025‑29824 as a Known Exploited Vulnerability, explicitly listing it in its catalog on April 8 and mandating mitigation or interruption of services by April 29 for Federal Civilian Executive Branch systems. Microsoft also recommended enabling cloud-based protections in Defender, Endpoint Detection and Response (EDR), and device discovery to extend defense-in-depth.
Signs of Exploitation & Detection Measures
Microsoft and cybersecurity firms released indicators of compromise (IOCs) and detection guidelines.
Logpoint, Symantec, and Tenable disclosed the detection criteria for PowerShell AD enumeration, called pipe generation by PipeMagic loaders, and Cloud-delivered Defender warnings for ransomware activity, DLL injections, and credential dumps.
Multi-platform threat intelligence encourages defenders to look for named pipe creations or odd parental processes that spawn MSBuild/MsBuild.exe. EDR warnings for file deletion in registry dumps or event logs should also be investigated immediately.
Implications & Strategic Takeaways
CVE‑2025‑29824 highlights a rising trend: ransomware actors exploiting zero-day flaws to gain SYSTEM-level privileges and establish persistent, high-impact activity. While such zero-day attacks are uncommon, their potential payoff drives ransomware operators to invest heavily in weaponizing them. CLFS, paired with memory theft, backup deletion, and log wiping, can devastate cybersecurity defenses and complicate recovery.
Microsoft’s rapid patch release and clarifications around unaffected systems (like Windows 11) were pivotal in curbing exploitation . Nonetheless, initial delays for some OS variants underscore the importance of multiple mitigation controls in enterprise environments.
Conclusion
CVE‑2025‑29824 is a sharp reminder that privilege escalation via kernel driver vulnerabilities remains a cornerstone of modern ransomware and post‑compromise strategies. By exploiting a use-after-free bug in the CLFS driver, attackers have repeatedly gained full SYSTEM privileges, dumped credentials, disabled backups, and deployed ransomware across global targets. Microsoft’s swift patch deployment, combined with collaborative detection and mitigation tools, helped blunt the impact, but defenders must remain vigilant.
Comprehensive strategies, not just patching, are required: rapid updates, EDR/XDR adoption, IOC-driven detection, and incident preparedness. As threat actors continue evolving, layered defenses, proactive monitoring, and zero-trust practices are no longer optional; they are essential.
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