Millions at Risk From Notepad++ DLL Hijacking Vulnerability

An old attack method has found a dangerous new target: Notepad++. A DLL hijacking flaw in the popular editor could give attackers a silent foothold on millions of machines worldwide.

The vulnerability allows attackers to replace legitimate plugin files with malicious DLLs, making every launch of Notepad++ a potential entry point for compromise. With proof-of-concept code already public, the likelihood of real-world attacks is rising fast.

Security researcher zer0t0 confirmed the scope of the flaw, noting that “…any installed Notepad++ is affected by this vulnerability.”

What’s the risk?

If exploited, attackers could leverage this flaw to escalate privileges, establish persistence, or deploy additional malware on systems.

The vulnerability (CVE-2025-56383) underscores the ongoing challenges in secure software development, particularly around how Windows applications load dynamic link libraries (DLLs). Details of the flaw, along with proof-of-concept (PoC) code, have been publicly released, increasing the likelihood of real-world exploitation.

How the attack works

At its core, the vulnerability arises from how Notepad++ loads plugin DLLs without enforcing strict path validation. Windows applications often search for required libraries in multiple directories. If the full path to a DLL is not specified, the application may inadvertently load a malicious file placed in a directory of higher priority.

Attackers can replace a plugin DLL, such as NppExport.dll, with a maliciously crafted version. To maintain functionality and avoid suspicion, the attacker can rename the legitimate DLL (e.g., original-NppExport.dll) and configure the fake one to proxy legitimate function calls. This technique ensures that the user sees no disruption in application performance, even as malicious payloads execute in the background.A successful exploit has already been demonstrated. When the compromised Notepad++ instance was launched, the attacker’s payload executed with the same permissions as the logged-in user, validated by a test message box.

While this specific demonstration was benign, the same method could deliver ransomware, keyloggers, or backdoors.

The existence of a PoC exploit elevates the urgency of this vulnerability. The security researcher confirmed that the exploit was demonstrated on Notepad++ v8.8.3, installed via the npp.8.8.3.Installer.x64.exe package. However, the underlying weakness likely affects all installed versions.

DLL hijacking is not a new attack vector. But its presence in a widely distributed application like Notepad++ dramatically broadens the attack surface. Since Notepad++ is commonly deployed in enterprise environments, compromised instances could become stepping stones in larger campaigns.

Mitigation strategies

Currently, there is no patch from the Notepad++ team addressing CVE-2025-56383. Until a fix is released, organizations and individuals should take the following steps:

• Restrict initial access vectors: Ensure endpoints are hardened against phishing, malware, and drive-by downloads, which attackers often use as a precursor to exploiting local vulnerabilities.
• Monitor file integrity: Implement file integrity monitoring (FIM) on directories such as Notepad++\plugins\ to detect unauthorized modifications to DLL files.
• Use official installers: Only download Notepad++ from the official project site to minimize supply-chain risks.
• Watch for persistence indicators: Security teams should analyze logs for repeated execution of Notepad++ with unexpected DLL loads.
• Broader hygiene practices: Apply least privilege access, enable multi-factor authentication (MFA), and segment critical systems to contain potential compromise.

The bigger picture

This vulnerability highlights a recurring issue in software security: the exploitation of legacy application design choices in modern threat landscapes. DLL hijacking has been documented for years, but attackers continue to find new ways to leverage it in widely used tools.

The risk is compounded by the availability of PoC code, which lowers the barrier for exploitation by both advanced persistent threat (APT) actors and opportunistic cybercriminals. In enterprise environments, the persistence and privilege escalation opportunities are concerning, as compromised endpoints can serve as launchpads for ransomware or lateral movement.

The discovery of CVE-2025-56383 in Notepad++ demonstrates how attackers can exploit seemingly minor flaws for significant gain. With a PoC already circulating, enterprises should act quickly to implement monitoring and defensive measures.

Since DLL hijacking is just one example of broader supply chain risks, the next step is learning how to prevent software supply chain attacks.