CVE-2026-23988: Rufus Privilege Escalation Vulnerability

CVE-2026-23988 Overview

CVE-2026-23988 is a Time-of-Check Time-of-Use (TOCTOU) race condition vulnerability affecting Rufus, a popular utility for creating bootable USB flash drives. The vulnerability exists in the src/net.c file during the creation, validation, and execution of the Fido PowerShell script. Because Rufus runs with elevated Administrator privileges but writes the script to the %TEMP% directory—which is writeable by standard users—without locking the file, a local attacker can exploit this race condition to replace the legitimate script with a malicious one between the file write operation and the execution step, resulting in arbitrary code execution with Administrator privileges.

Critical Impact

Local attackers can escalate privileges to Administrator level by exploiting a race condition in how Rufus handles PowerShell script execution, potentially leading to complete system compromise.

Affected Products

• Rufus versions 4.11 and below

Discovery Timeline

• 2026-01-22 - CVE CVE-2026-23988 published to NVD
• 2026-01-22 - Last updated in NVD database

Technical Details for CVE-2026-23988

Vulnerability Analysis

This vulnerability is classified under CWE-367 (Time-of-Check Time-of-Use Race Condition). The core issue stems from a fundamental flaw in how Rufus handles the Fido PowerShell script lifecycle. When Rufus needs to download Windows ISO images, it creates a PowerShell script in the user's %TEMP% directory, validates it, and then executes it. However, there is a window of opportunity between these operations where the file is not locked or protected.

The attack requires local access and some user interaction, but the impact is significant given that successful exploitation grants the attacker Administrator-level code execution. This represents a privilege escalation path from a standard user account to full administrative control over the system.

Root Cause

The root cause lies in the insecure file handling within src/net.c. Rufus writes the Fido PowerShell script to a world-writeable location (%TEMP%) without implementing proper file locking mechanisms. The application fails to ensure atomicity between the file write, validation, and execution operations. This creates a classic TOCTOU vulnerability where the state of the file can change between the time it is checked (validated) and the time it is used (executed).

Attack Vector

The attack requires local access to the target system. An attacker with standard user privileges can monitor the %TEMP% directory for the creation of the Fido PowerShell script. When detected, the attacker rapidly replaces the legitimate script content with malicious code before Rufus executes it. Since Rufus runs with Administrator privileges, the malicious script inherits these elevated permissions.

The attack flow involves:

1. The attacker sets up monitoring on the %TEMP% directory
2. A legitimate user runs Rufus and triggers the Fido script functionality
3. Rufus writes the PowerShell script to %TEMP%
4. The attacker's process detects the file and replaces its contents with malicious code
5. Rufus executes the now-malicious script with Administrator privileges

The vulnerability requires user interaction (the victim must run Rufus and trigger the vulnerable code path), but the window for exploitation can be expanded through various techniques to make the race condition more reliable.

Detection Methods for CVE-2026-23988

Indicators of Compromise

• Unexpected PowerShell script modifications or replacements in user %TEMP% directories
• Suspicious processes monitoring or rapidly accessing the %TEMP% directory during Rufus execution
• PowerShell execution events spawned by Rufus containing unexpected commands or payloads
• Anomalous privilege escalation patterns originating from standard user accounts

Detection Strategies

• Monitor for file system race condition patterns targeting the %TEMP% directory, particularly rapid file modifications
• Implement endpoint detection rules for suspicious PowerShell script execution patterns spawned by rufus.exe
• Deploy behavioral analysis to detect privilege escalation attempts following Rufus execution
• Use SentinelOne's Behavioral AI to identify TOCTOU exploitation patterns and anomalous script replacements

Monitoring Recommendations

• Enable detailed PowerShell script block logging and transcription to capture executed script content
• Configure file integrity monitoring on temporary directories during Rufus execution
• Implement process monitoring to track parent-child relationships between rufus.exe and spawned processes
• Review Windows Security Event logs for anomalous process creation with elevated privileges

How to Mitigate CVE-2026-23988

Immediate Actions Required

• Update Rufus to version 4.12_BETA or later, which contains the security fix
• Restrict execution of Rufus to trusted environments until patching is complete
• Consider running Rufus in isolated environments where standard users cannot access the same %TEMP% directory
• Monitor systems running vulnerable Rufus versions for signs of exploitation

Patch Information

The vulnerability has been addressed in Rufus version 4.12_BETA. The fix is documented in the GitHub commit which implements proper file handling to prevent the race condition. Users should download the patched version from the official GitHub release page. Additional details about the vulnerability and its remediation can be found in the GitHub Security Advisory.

Workarounds

• Avoid using the Fido download functionality in vulnerable Rufus versions; manually download ISO images from official Microsoft sources instead
• Run Rufus in an isolated virtual machine or sandbox environment to contain potential exploitation
• Implement application whitelisting to prevent unauthorized script execution from the %TEMP% directory
• Consider using a dedicated administrative account with a separate user profile to isolate the %TEMP% directory from standard users

# Configuration example
# Verify Rufus version before use
rufus.exe --version

# If vulnerable, download patched version from official source
# https://github.com/pbatard/rufus/releases/tag/v4.12_BETA