CVE-2025-56383: Notepad++ v8.8.3 DLL Hijacking RCE Flaw

CVE-2025-56383 Overview

A DLL hijacking vulnerability exists in Notepad++ version 8.8.3 that allows attackers to execute arbitrary malicious code by replacing legitimate DLL files. This vulnerability (classified as CWE-427: Uncontrolled Search Path Element) occurs when the application loads DLL files from an insecure location, enabling attackers with local access to substitute malicious DLL files that will be executed with the privileges of the Notepad++ process.

Note: This vulnerability is disputed by multiple parties because the exploitable behavior only occurs when a user installs Notepad++ into a directory tree that allows write access by arbitrary unprivileged users, which is not the default installation configuration.

Critical Impact

Successful exploitation allows local attackers to achieve code execution with the privileges of the Notepad++ process, potentially leading to complete system compromise, data theft, or persistence mechanisms.

Affected Products

• Notepad++ v8.8.3
• Potentially earlier versions with similar DLL loading behavior

Discovery Timeline

• 2025-09-26 - CVE-2025-56383 published to NVD
• 2025-11-19 - Last updated in NVD database

Technical Details for CVE-2025-56383

Vulnerability Analysis

This DLL hijacking vulnerability stems from how Notepad++ searches for and loads dynamic link libraries during application startup or runtime operations. When the application attempts to load a DLL, Windows follows a specific search order that includes the application directory and other locations in the system PATH. If an attacker can place a malicious DLL with the expected filename in a location that is searched before the legitimate DLL location, the malicious code will be executed instead.

The dispute surrounding this CVE centers on the requirement that the installation directory must be writable by unprivileged users. Standard Windows installations place applications in C:\Program Files or C:\Program Files (x86), which require administrative privileges to modify. However, installations in user-writable locations (such as portable installations or custom directories) may be vulnerable.

Root Cause

The root cause is the application's reliance on the Windows DLL search order without implementing sufficient safeguards such as absolute path loading, DLL signature verification, or secure search path configuration. When combined with an insecure installation directory, this creates an exploitable condition where arbitrary DLL files can be loaded and executed.

Attack Vector

The attack requires local access to the system and write permissions to either the Notepad++ installation directory or a directory that appears earlier in the DLL search path. An attacker would craft a malicious DLL with the same name as a legitimate DLL that Notepad++ loads, then place this file in a searchable location. When a user launches Notepad++, the malicious DLL is loaded and executed with the user's privileges.

The exploitation scenario typically involves:

1. Identifying DLL files that Notepad++ loads during startup
2. Creating a malicious DLL with the same filename containing attacker-controlled code
3. Placing the malicious DLL in the application directory or another location in the search path
4. Waiting for a user to launch Notepad++, triggering execution of the malicious code

For technical details and proof-of-concept information, refer to the GitHub PoC repository.

Detection Methods for CVE-2025-56383

Indicators of Compromise

• Unexpected DLL files appearing in Notepad++ installation directories
• DLL files in application directories with recent modification timestamps not matching legitimate updates
• Unsigned or improperly signed DLL files in the Notepad++ directory
• Process execution anomalies when Notepad++ starts, such as unexpected child processes or network connections

Detection Strategies

• Monitor file system changes in Notepad++ installation directories for new or modified DLL files
• Implement application whitelisting to detect unauthorized DLL loading
• Use endpoint detection tools to identify DLL side-loading attempts during Notepad++ execution
• Compare DLL file hashes against known-good values from official Notepad++ releases

Monitoring Recommendations

• Enable Windows Event Logging for module load events (Event ID 7) to track DLL loading behavior
• Configure SentinelOne to monitor for suspicious DLL loading patterns in user-writable directories
• Implement file integrity monitoring on the Notepad++ installation directory
• Review process creation events for Notepad++ to detect anomalous behavior following launch

How to Mitigate CVE-2025-56383

Immediate Actions Required

• Install Notepad++ in a protected directory such as C:\Program Files or C:\Program Files (x86) that requires administrative privileges to modify
• Review existing Notepad++ installations to ensure they are not located in user-writable directories
• Audit directory permissions on the Notepad++ installation folder and remove write access for unprivileged users
• Consider upgrading to the latest version of Notepad++ from the official repository

Patch Information

As this vulnerability is disputed and depends on installation configuration rather than a code flaw, no specific patch has been released. The mitigation focuses on proper installation practices. Organizations should verify that Notepad++ is installed in directories with appropriate access controls. For additional guidance, refer to the Vicarius Mitigation Guide.

Workarounds

• Relocate portable Notepad++ installations from user-writable locations to protected system directories
• Apply restrictive NTFS permissions to the Notepad++ installation directory, allowing only administrators to write
• Use Windows Defender Application Control (WDAC) or AppLocker policies to prevent execution of unauthorized DLLs
• Implement SentinelOne endpoint protection to detect and block DLL hijacking attempts

# Verify and restrict permissions on Notepad++ installation directory
# Run as Administrator in PowerShell

# Check current permissions
icacls "C:\Program Files\Notepad++"

# Remove write permissions for Users group (if incorrectly set)
icacls "C:\Program Files\Notepad++" /remove:g "Users"

# Ensure only Administrators have modify access
icacls "C:\Program Files\Notepad++" /grant:r "Administrators:(OI)(CI)F"
icacls "C:\Program Files\Notepad++" /grant:r "SYSTEM:(OI)(CI)F"
icacls "C:\Program Files\Notepad++" /grant:r "Users:(OI)(CI)RX"