A newly discovered DLL hijacking vulnerability in Notepad++, the popular source code editor, could allow attackers to execute arbitrary code on a victim’s machine.
Tracked as CVE-2025-56383, the flaw exists in version 8.8.3 and potentially affects all installed versions of the software, putting millions of users at risk.
The vulnerability enables a local attacker to achieve code execution by planting a malicious DLL file in a location where the application will load it. This type of attack undermines the integrity of the application and can be used to establish persistence or escalate privileges on a compromised system.
PoC Exploit Released
DLL (Dynamic Link Library) hijacking exploits the way Windows applications search for and load required libraries. If an application searches for a DLL without specifying a full path, it may look in several directories in a predefined order.
An attacker can place a malicious DLL with the same name as a legitimate one in a directory that is searched before the actual library’s location. When the user launches the application, the malicious DLL is loaded and executed instead of the intended one.
In the case of Notepad++, the vulnerability can be exploited by targeting the DLLs associated with its plugins. According to the proof-of-concept, an attacker can replace a plugin file, such as NppExport.dll, located in the Notepad++pluginsNppExport directory, with a custom-crafted malicious DLL.
To remain undetected and ensure the application continues to function normally, the attacker can rename the original DLL (e.g., to original-NppExport.dll) and have the malicious replacement forward all legitimate function calls to it.
This technique, known as proxying, makes the application’s behavior appear seamless to the user while the malicious payload executes in the background.
The provided example demonstrates this file replacement. The malicious NppExport.dll is significantly smaller than the original-NppExport.dll, indicating it contains different code.
Upon launching Notepad++.exe, the application loads the malicious DLL, leading to the execution of the attacker’s code.
A successful exploit was demonstrated by the appearance of a test message box, confirming that the arbitrary code was executed with the same permissions as the user running Notepad++.
Mitigations
The primary threat from this vulnerability is local code execution. An attacker who has already gained initial access to a system through malware, phishing, or other means can use this flaw to establish persistence.
By hijacking a DLL in a commonly used application like Notepad++, the attacker’s code will run every time the user opens the editor, ensuring the malware survives system reboots.
While the demonstration was performed on Notepad++ v8.8.3 installed via the official npp.8.8.3.Installer.x64.exe, the underlying issue is fundamental to how the application loads its components, suggesting that any installed version could be vulnerable.
Currently, there is no official patch from the Notepad++ developers to address CVE-2025-56383. Users are advised to exercise caution and ensure their systems are free from prior infections
System administrators should consider implementing file integrity monitoring on application directories to detect unauthorized modifications.
Until a fix is released, users should only download Notepad++ from official sources and be wary of any unexpected behavior from the application.
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