CVE-2026-26153: Windows EFS Privilege Escalation Flaw

CVE-2026-26153 Overview

CVE-2026-26153 is an out-of-bounds read vulnerability in the Windows Encrypting File System (EFS) that enables an authorized attacker to elevate privileges locally. This memory corruption flaw (CWE-125) occurs when EFS improperly reads memory beyond the bounds of an allocated buffer, potentially allowing attackers with local access to gain elevated system privileges.

Critical Impact

Local privilege escalation through out-of-bounds read in Windows EFS could allow attackers with low-privilege access to achieve complete system compromise with high impact to confidentiality, integrity, and availability.

Affected Products

• Windows Encrypting File System (EFS)
• Windows Operating Systems with EFS enabled

Discovery Timeline

• 2026-04-14 - CVE CVE-2026-26153 published to NVD
• 2026-04-14 - Last updated in NVD database

Technical Details for CVE-2026-26153

Vulnerability Analysis

This vulnerability stems from an out-of-bounds read condition (CWE-125) within the Windows Encrypting File System (EFS) component. EFS is a feature built into Windows that provides filesystem-level encryption to protect sensitive data. The vulnerability allows an authenticated local attacker to read memory outside the intended buffer boundaries, which can be leveraged to disclose sensitive information or manipulate program execution flow to achieve privilege escalation.

The attack requires local access to the target system and low privileges to execute. No user interaction is required for exploitation, making this a particularly concerning vulnerability for multi-user environments or systems where attackers may already have limited access through other means.

Root Cause

The root cause is improper bounds checking in the EFS component when processing certain data structures. When EFS handles specific operations, it fails to properly validate the length or boundaries of memory read operations, resulting in an out-of-bounds read condition. This memory safety violation allows attackers to access memory regions beyond what was intended, potentially exposing sensitive kernel information or enabling exploitation chains for privilege escalation.

Attack Vector

The attack vector is local, requiring the attacker to have existing access to the target system with low-level privileges. The exploitation scenario involves:

1. An attacker with valid credentials or initial foothold on a Windows system
2. Crafting malicious input or triggering specific EFS operations that exploit the bounds checking flaw
3. Leveraging the out-of-bounds read to disclose sensitive memory contents or corrupt adjacent memory
4. Using the disclosed information or memory corruption to escalate privileges to SYSTEM level

The vulnerability is exploited through the EFS subsystem, which handles encryption and decryption of files on NTFS volumes. For detailed technical information, refer to the Microsoft Security Update for CVE-2026-26153.

Detection Methods for CVE-2026-26153

Indicators of Compromise

• Unusual EFS-related service crashes or error events in Windows Event Logs
• Unexpected privilege escalation activity from low-privileged user accounts
• Anomalous access patterns to encrypted files or EFS certificate stores
• Memory access violations logged in system diagnostics related to EFS operations

Detection Strategies

• Monitor Windows Security Event Logs for privilege escalation events (Event ID 4672, 4673)
• Deploy endpoint detection solutions to identify suspicious EFS API calls and memory access patterns
• Implement behavioral analysis for processes attempting to interact with EFS in unusual ways
• Use SentinelOne's behavioral AI to detect exploitation attempts targeting EFS components

Monitoring Recommendations

• Enable detailed auditing for EFS-related operations in Windows Security Policy
• Configure alerts for unexpected SYSTEM-level process creation from low-privilege sessions
• Monitor for suspicious process behaviors associated with local privilege escalation techniques
• Deploy memory protection mechanisms to detect out-of-bounds read attempts

How to Mitigate CVE-2026-26153

Immediate Actions Required

• Apply the latest Microsoft security updates for affected Windows systems immediately
• Review and restrict EFS usage to essential systems and users only
• Implement principle of least privilege to limit potential attacker access
• Enable advanced threat protection features on endpoints to detect exploitation attempts

Patch Information

Microsoft has released a security update addressing this vulnerability. System administrators should apply the patch available through Windows Update or the Microsoft Update Catalog. For detailed patch information and affected product versions, refer to the Microsoft Security Response Center advisory.

Workarounds

• Restrict local user access to systems where EFS is critical infrastructure
• Consider disabling EFS on systems where file-level encryption is not required
• Implement application whitelisting to prevent unauthorized code execution
• Deploy network segmentation to limit lateral movement opportunities for attackers with initial access

# Verify EFS service status and consider disabling if not required
sc query EFS
# To disable EFS service (if not needed)
sc config EFS start= disabled
sc stop EFS