CVE-2025-29824: SYSTEM Privilege Escalation in Windows CLFS Driver (Use-After-Free)

HERMES

HERMES THREAT SCORE & WINDOWS KERNEL COMPROMISE RISK

Target: Microsoft Windows Common Log File System (clfs.sys)

Confidence: 98%

89 / 100

HIGH

Measures real-world operational relevance, exploit weaponization, and active threat posture.

Dimension Breakdown

Exploitability 18 / 20

Threat Activity 19 / 20

Weaponization 20 / 20

Exposure 15 / 20

Prevalence 20 / 20

Impact 19 / 20

Exploit Maturity 20 / 20

Attack Chain Potential 20 / 20

⚖️ Divergence & Operational Rationale

Hermes assesses CVE-2025-29824 at an HTS of 89 (HIGH). This kernel flaw in clfs.sys provides deterministic local privilege escalation. Actively exploited as a zero-day by access brokers and ransomware affiliates (BlackCat, Nokoyawa), it allows adversaries to disable EDR sensors and dump LSASS credentials.

🕸️ Connected Knowledge Graph & Provenance

CVE-2025-29824: SYSTEM Privilege Escalation in Windows CLFS Driver (Use-After-Free)VULNERABILITY

Connected Nodes: 1

Active Relationships (Outgoing)

→ affectsPRODUCTMicrosoft Windows & Windows Server

98% VERY_HIGH

Software platform affected by security vulnerabilities and agentic attack patterns.

🔍 Why is this related? (Evidence & Provenance)

“Confirmed security vulnerability in Microsoft Windows & Windows Server documented in Hermes dossier.”

Supporting Verified Evidence:

[vulnerability_report]
[government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

1. Identification

Parameter	Technical Specification	Operational Impact
CVE Identifier	`CVE-2025-29824`	Official MITRE / NVD entry
Associated CWE	`CWE-416`: Use-After-Free	Kernel dangling pointer manipulation
CVSS v3.1 Score	7.8 HIGH	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`
CVSS v4.0 Score	7.3 HIGH	`CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`
Applicable CPEs	`cpe:2.3:o:microsoft:windows_10::::::::` `cpe:2.3:o:microsoft:windows_11::::::::` `cpe:2.3:o:microsoft:windows_server_2019::::::::` `cpe:2.3:o:microsoft:windows_server_2022::::::::` `cpe:2.3:o:microsoft:windows_server_2025::::::::`	Enterprise Windows endpoints and domain servers
Fixed Versions	April 2025 Patch Tuesday (KB5036893, KB5036892, etc.)	Cumulative security updates

2. Exploitation

CISA KEV: Added on April 8, 2025; confirmed ransomware deployment usage (KnownRansomwareCampaignUse = Known).
EPSS Score: 0.13904 (Percentile: 96.3%).
Operational Status: Confirmed in-the-wild zero-day exploitation. Manipulates crafted Base Log File (.blf) records parsed by clfs.sys.
Weaponization: Integrated into post-exploitation frameworks and cybercriminal intrusion playbooks.

3. Threat Intelligence

Threat Actors: FIN7, Storm-0978, Nokoyawa, and BlackCat/ALPHV affiliates.
Attack Chain: Serves as the primary privilege escalation mechanism once initial access is achieved, swapping process tokens with the kernel System process (EPROCESS.Token).

4. Detection and Forensics

Sigma Rule

title: Suspicious BLF File Creation and CLFS Kernel Elevation (CVE-2025-29824)
id: 29824-clfs-uaf-elevation-en
status: production
description: Detects the creation of abnormal CLFS log files in temp folders followed by privilege transitions.
logsource:
  category: file_event
  product: windows
detection:
  selection_path:
    TargetFilename|endswith: '.blf'
    TargetFilename|contains:
      - '\AppData\Local\Temp\'
      - '\Windows\Temp\'
  selection_process:
    Image|endswith:
      - '\cmd.exe'
      - '\powershell.exe'
      - '\rundll32.exe'
  condition: selection_path and selection_process
level: high

MITRE ATT&CK

T1068: Exploitation for Privilege Escalation
T1562.001: Impair Defenses: Disable or Modify Tools
T1003.001: OS Credential Dumping: LSASS Memory

5. Remediation and Hardening

Install Security Updates: Immediately install the April 2025 cumulative Windows updates.
Reboot Mandatory: A full host restart is required to update the clfs.sys kernel driver in memory.
Attack Surface Reduction (ASR): Enforce rules that restrict child process creation by scripting interpreters.

6. Enterprise Exploitation Scenario

« What happens if this vulnerability is exploited in an enterprise? »
Section titled “« What happens if this vulnerability is exploited in an enterprise? »”

Initial Beachhead: An attacker compromises a corporate workstation through phishing or credential stuffing on an exposed remote service.

Instant Kernel Takeover: Running with standard domain user permissions, the attacker launches the CLFS exploit binary. By triggering the Use-After-Free flaw in clfs.sys, the attacker’s process token is overwritten with NT AUTHORITY\SYSTEM.

Sensor Disabling: With SYSTEM privileges, the threat actor disables endpoint protection software, bypasses tamper protection, and suppresses telemetry logs.

Enterprise-Wide Ransomware: The attacker extracts all cached credentials from LSASS, pivots across administrative shares, and encrypts central backup and file servers.