Notepad++ DLL Hijack Flaw Lets Attackers Run Malicious Code

Security researchers have identified a critical DLL hijacking vulnerability in Notepad++ version 8.8.3, tracked as CVE-2025-56383.

This flaw enables attackers to execute arbitrary code by replacing legitimate Dynamic Link Library (DLL) files within the application’s plugin directory with malicious versions that maintain the same export functions.

Technical Details

The vulnerability specifically targets Notepad++’s plugin system, particularly the NppExport.dll file located in the Notepad++pluginsNppExport directory.

Attackers can exploit this weakness by creating a malicious DLL file with identical export functions that forward calls to the original DLL while simultaneously executing harmful code.

When users launch Notepad++, the application automatically loads these plugin DLLs, providing an opportunity for malicious code execution.

The attack method involves replacing the original DLL file with a crafted version that appears legitimate but contains embedded malicious functionality.

Successful exploitation requires attackers to have local file system access and the ability to modify files within the Notepad++ installation directory.

While this limits the attack scope to scenarios where attackers already have some level of system access, it can serve as an effective privilege escalation or persistence mechanism.

The vulnerability has been assigned a CVSS 3.1 score of 7.8 (High), indicating significant security implications.

The attack vector is classified as local with low complexity, requiring low privileges and user interaction to succeed.

Security researcher zer0t0 has published a proof-of-concept demonstration on GitHub, showing how the vulnerability can be exploited using the NppExport.dll plugin.

 The demonstration includes replacing the original DLL with a malicious version named original-NppExport.dll while maintaining the forged NppExport.dll in its place.

While no official patch has been released yet, users should exercise caution when downloading Notepad++ from unofficial sources or allowing untrusted software to modify their system.

Organizations should monitor their Notepad++ installations for unauthorized changes to plugin DLL files.

The vulnerability affects not only version 8.8.3 but potentially other versions of Notepad++ that use similar plugin loading mechanisms.

Users should verify the integrity of their plugin files and consider restricting write access to the Notepad++ installation directory.

This discovery highlights the importance of secure application design and the need for robust file integrity verification in software that loads external components.

As Notepad++ remains widely used across various environments, addressing this vulnerability should be a priority for both users and the development team.

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