Full Report
Threat actors with links to the Play ransomware family exploited a recently patched security flaw in Microsoft Windows as a zero-day as part of an attack targeting an unnamed organization in the United States. The attack, per the Symantec Threat Hunter Team, part of Broadcom, leveraged CVE-2025-29824, a privilege escalation flaw in the Common Log File System (CLFS) driver. It was patched by
Analysis Summary
This incident report summarizes the activity observed against an unnamed US organization, focusing on a specific attack chain involving the Play ransomware group leveraging a recently patched Windows zero-day vulnerability.
# Incident Report: Play Ransomware Exploitation of Windows CLFS Zero-Day (CVE-2025-29824)
## Executive Summary
Threat actors associated with the Play ransomware family exploited a zero-day vulnerability in the Windows Common Log File System (CLFS) driver (CVE-2025-29824) to gain elevated access within an unnamed US organization. The attack utilized bespoke tools, including the Grixba information stealer, to perform reconnaissance and local privilege escalation, though no final ransomware payload was deployed in the observed activity. Response actions involved analyzing the indicators left behind, confirming the zero-day exploitation, and reinforcing the need for rapid patching cycles against high-impact vulnerabilities.
## Incident Details
- **Discovery Date:** Recent disclosure by Symantec Threat Hunter Team (Post-Patch Date)
- **Incident Date:** Occurred prior to Microsoft patching CVE-2025-29824 last month.
- **Affected Organization:** Unnamed Organization
- **Sector:** Undisclosed (Targeting implied corporate entity)
- **Geography:** United States
## Timeline of Events
### Initial Access
- **Date/Time:** Unknown, prior to patch availability.
- **Vector:** Likely a public-facing Cisco Adaptive Security Appliance (ASA).
- **Details:** Attackers gained an initial foothold, potentially via an unstated method exploiting the ASA, before pivoting to an internal Windows machine.
### Lateral Movement
- **Details:** Attackers moved from the initial compromise point to another Windows machine on the target network. Discovery commands were run to gather Active Directory information.
### Data Exfiltration/Impact
- **Details:** The primary impact observed was the execution of privilege escalation routines and credential dumping. The use of the Grixba information stealer suggests data theft was intended, though the report states no final ransomware payload was deployed. Sensitive data exfiltration (consistent with Play's double extortion) may have occurred prior to the observed endpoint activity.
### Detection & Response
- **Details:** The incident was brought to light and analyzed by the Symantec Threat Hunter Team. Response actions are implied to be focused on analysis following the discovery of the malicious artifacts and activity.
## Attack Methodology
- **Initial Access:** Likely leveraged a vulnerable public-facing Cisco ASA.
- **Persistence:** Achieved via DLL injection into the `winlogon.exe` process using a dropped DLL (`clssrv.inf`).
- **Privilege Escalation:** Exploited CVE-2025-29824 (CLFS driver flaw) and used a batch file (`servtask.bat`) to dump SAM, SYSTEM, and SECURITY Registry hives, and create a new local administrator user named "LocalSvc."
- **Defense Evasion:** Dropped files masqueraded as Palo Alto Networks software (e.g., "paloaltoconfig.exe").
- **Credential Access:** Dumped critical Registry hives (SAM, SYSTEM).
- **Discovery:** Ran commands to map Active Directory structure and saved results to a CSV file.
- **Lateral Movement:** Pivoted to another Windows machine from the ASA foothold.
- **Collection:** Used the bespoke information stealer, Grixba.
- **Exfiltration:** Implied, given Play's known double extortion tactics.
- **Impact:** Local privilege escalation and data staging; no final encryption was deployed in this observed instance.
## Impact Assessment
- **Financial:** Not disclosed.
- **Data Breach:** Potential theft of PII/sensitive data (implied by Play's TTPs and Grixba use).
- **Operational:** Potential operational disruption due to reconnaissance and account creation if the attack had progressed to encryption.
- **Reputational:** Unknown.
## Indicators of Compromise
- **Network indicators:** (None explicitly defanged in the text, Cisco ASA vulnerability is key entry point).
- **File indicators:**
- Files dropped in `C:\ProgramData\SkyPDF`: `PDUDrv.blf` (CLFS artifact) and `clssrv.inf` (DLL).
- Masquerading executables: "paloaltoconfig.exe" and "paloaltoconfig.dll".
- **Behavioral indicators:**
- Exploitation of CVE-2025-29824.
- Execution of `servtask.bat` and `cmdpostfix.bat`.
- Use of Grixba information stealer.
- Dumping of Registry hives from memory.
- Creation of user "LocalSvc" and adding it to the Administrator group.
## Response Actions
- **Containment:** Not explicitly detailed, but would involve isolating affected systems and blocking related network activity.
- **Eradication:** Removal of Grixba, dropped files (`.blf`, `.inf`, executables), batch files, and the suspicious "LocalSvc" user account.
- **Recovery:** Password resets for affected accounts, rolling back changes made by the batch scripts, and full validation of AD integrity.
## Lessons Learned
- Zero-day vulnerabilities, even those recently patched, are actively weaponized by sophisticated ransomware groups like Play immediately upon exploitation maturity.
- Attackers are using complex, multi-stage approaches involving external-facing initial access (ASA) followed by kernel-level privilege escalation (CVE-2025-29824).
- The presence of information stealers (Grixba) indicates data theft is a primary objective, even if the final ransomware execution is aborted or not observed.
## Recommendations
- Prioritize patching for critical vulnerabilities like CVE-2025-29824 immediately upon release, especially for internet-facing equipment (like ASA devices).
- Implement enhanced monitoring on Windows CLFS activity and unusual DLL injection into system processes like `winlogon.exe`.
- Review and lockdown configuration management for public-facing security appliances to prevent them from becoming initial pivot points.
- Implement robust detection rules specifically targeting the behaviors of the Grixba information stealer.