CVE-2019-16294 in Notepad++
Summary
by MITRE
SciLexer.dll in Scintilla in Notepad++ (x64) before 7.7 allows remote code execution or denial of service via Unicode characters in a crafted .ml file.
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Analysis
by VulDB Data Team • 11/14/2025
CVE-2019-16294 represents a critical vulnerability in the Scintilla library component of Notepad++ editor affecting versions prior to 7.7. This vulnerability specifically targets the SciLexer.dll module which handles syntax highlighting for various programming languages including ML. The flaw manifests when processing malformed Unicode sequences within .ml files, which are typically used for Standard ML programming language source code. The vulnerability falls under CWE-129, representing an improper validation of array index, where the application fails to properly validate Unicode character sequences before processing them. This allows attackers to craft malicious .ml files containing specially constructed Unicode characters that trigger buffer overflows or memory corruption during the lexing process. The attack vector is particularly concerning as it enables remote code execution when users open crafted files, making it a significant threat in scenarios where users might encounter untrusted code or be tricked into opening malicious files. The vulnerability impacts both Windows x64 and x86 architectures, though the x64 version was specifically mentioned in the CVE description. When exploited, the vulnerability can lead to arbitrary code execution with the privileges of the affected user, potentially allowing attackers to install malware, steal data, or compromise the entire system. The denial of service aspect of this vulnerability means that even simply opening a malicious file can crash the Notepad++ application, disrupting user workflows and potentially enabling more sophisticated attacks. The root cause lies in insufficient input validation within the Scintilla lexer component, which fails to properly handle edge cases in Unicode character processing. This vulnerability aligns with ATT&CK technique T1059.007, which covers command and scripting interpreter usage, as attackers could leverage this vulnerability to execute arbitrary commands through the compromised Notepad++ process. The exploitation process typically involves crafting a .ml file with malformed Unicode sequences that cause the lexer to access memory beyond allocated buffers, leading to unpredictable behavior. Organizations using Notepad++ should immediately update to version 7.7 or later to mitigate this vulnerability, as the fix includes proper bounds checking and Unicode validation within the Scintilla library. System administrators should also implement file scanning policies for .ml files from untrusted sources and consider disabling automatic syntax highlighting for potentially malicious files. The vulnerability demonstrates the importance of proper input validation in text processing libraries and highlights the risks associated with complex lexing engines that must handle multiple character encodings. This issue underscores the need for regular security updates and the potential for seemingly benign text processing components to become attack vectors in modern software environments. The impact extends beyond individual users to enterprise environments where Notepad++ is commonly used for code review and documentation tasks, making this vulnerability particularly dangerous in development and operations contexts.