CVE-2025-32713
clfs.sys -- heap-based buffer overflow allows elevation of privilege
Summary
| Field | Value |
|---|---|
| Driver | clfs.sys |
| Vulnerability Class | Buffer Overflow (Heap) |
| CVSS | 7.8 |
| Exploited ITW | No |
| Patch Date | June 10, 2025 |
Root Cause
The Common Log File System driver has become one of the most reliably exploited kernel attack surfaces in Windows, with a lineage stretching from CVE-2022-37969 through CVE-2025-32706 and beyond. CVE-2025-32713 continues that pattern.
The vulnerability sits in how clfs.sys processes metadata structures within Base Log Files (BLF). When the driver parses a crafted BLF, it fails to validate the size of certain metadata fields before copying them into a heap buffer. The result is a classic heap-based buffer overflow: data spills past the end of the allocation and corrupts whatever sits next to it in the NonPagedPoolNx.
What makes this particularly interesting is the consistency of the attack surface. CLFS BLF files are user-writable artifacts that get parsed in kernel context with full trust. Every new CLFS vulnerability follows the same fundamental pattern: craft a file on disk, trick the kernel into parsing it, and exploit the gap between what the file claims and what the kernel expects. S2W published a detailed analysis showing how the metadata corruption maps to specific fields in the BLF container context structures.
Exploitation
An attacker places a malformed CLFS log file in a user-writable directory. When the file is opened and processed by the kernel, the heap overflow corrupts adjacent pool allocations. By shaping the heap layout before triggering the overflow (through techniques like named pipe spraying), the attacker controls what gets overwritten. The corrupted adjacent object provides a primitive for token manipulation, ultimately yielding SYSTEM privileges.
Exploitation Primitive
Crafted CLFS log file -> heap buffer overflow
-> adjacent pool object corruption -> token manipulation -> SYSTEM
Broader Significance
CVE-2025-32713 is another data point in the argument that CLFS needs architectural hardening, not just point fixes. The BLF file format gives attackers a stable, well-documented attack surface where they control the input (the file), the parsing happens in ring 0, and the corruption targets are predictable kernel pool objects. Microsoft has been patching individual bounds checks for years, but the fundamental trust model -- kernel code parsing user-writable files with minimal validation -- remains unchanged.