Full Report
Exploit used by Play-linked attackers targets the CVE-2025-29824 zero-day vulnerability patched on April 8.
Analysis Summary
# Vulnerability: Windows Common Log File System Driver Privilege Escalation (Zero-Day)
## CVE Details
- CVE ID: CVE-2025-29824
- CVSS Score: N/A (Severity implied High due to Zero-Day and EoP context)
- CWE: N/A (Specific CWE not provided, likely related to Improper Input Validation in a kernel driver)
## Affected Systems
- Products: Microsoft Windows
- Versions: Versions prior to the April 8, 2025 patch date.
- Configurations: Systems utilizing the Common Log File System Driver (`clfs.sys`).
## Vulnerability Description
This is a time-of-check to time-of-use (TOCTOU) vulnerability within the Windows Common Log File System (CLFS) kernel driver (`clfs.sys`). An attacker can trigger a race condition between two threads attempting to interact with a newly opened log file handle.
1. **Thread 1 (Cleanup):** Calls `CloseHandle()`, leading the kernel to send an `IRP_MJ_CLEANUP` request to the CLFS driver, which causes the driver to deallocate the internal `CClfsLogCcb` structure associated with the file operation via its pointer stored in the `FILE_OBJECT`'s `FsContext2` field.
2. **Thread 2 (Operation):** Simultaneously calls `DeviceIoControl()` targeting the same file handle, which results in an `IRP_MJ_DEVICE_CONTROL` request being sent to the CLFS driver.
If the `IRP_MJ_CLEANUP` completes before `IRP_MJ_DEVICE_CONTROL`, the CLFS driver attempts to use the pointer in `FsContext2` which now references already deallocated memory (a use-after-free condition). This allows the attacker to modify kernel memory, leading to **Local Privilege Escalation (LPE)**.
## Exploitation
- Status: **Exploited in the wild** (Used by Play ransomware threat actor "Balloonfly" prior to disclosure/patching).
- Complexity: Low (Exploited successfully by threat actors to gain system-level access).
- Attack Vector: Local (Requires the attacker to already have some level of access to execute the exploit code, although the initial infection vector might have been network-facing, such as a vulnerable Cisco ASA).
## Impact
- Confidentiality: Potentially High (Full system compromise allows data exfiltration).
- Integrity: High (Arbitrary kernel memory write leads to complete system integrity compromise).
- Availability: Potentially High (Kernel crash/BSOD, or system compromise leading to data destruction/encryption).
## Remediation
### Patches
- **Microsoft Patch released April 8, 2025.** Users must apply the corresponding Windows security update.
### Workarounds
- No specific workarounds are detailed in the source text, however, given this is a kernel LPE exploit, strict application of the patch is mandatory. Restricting local user privileges remains a general mitigation.
## Detection
- **Indicators of Compromise (IOCs):**
* `858efe4f9037e5efebadaaa70aa8ad096f7244c4c4aeade72c51ddad23d05bfe` – `go.exe` (CVE-2025-29824 exploit)
* Files created during exploitation in `C:\ProgramData\SkyPDF` (e.g., `PDUDrv.blf`).
- **Detection Methods:** Endpoint Detection and Response (EDR) solutions should monitor for suspicious process injection, unusual handle operations referencing CLFS driver files, and process interaction with the file path `\\.\LOG:\??\C:\ProgramData\SkyPDF\PDUDrv` preceding the patch date. Monitoring for the execution of the Grixba infostealer is also advised.
## References
- Vendor Advisory: Microsoft Security Update Guide (Referencing CVE-2025-29824)
- Secondary Link (Context): hxxps://www.security.com/threat-intelligence/play-ransomware-volume-shadow-copy
- Protection Bulletin: hxxps://www.broadcom.com/support/security-center/protection-bulletin