Executive brief
Notepad++ is a popular open-source text and source code editor for Windows. A vulnerability in how the application handles internal communication messages allows other programs running on the same computer to force Notepad++ to crash. This results in a denial-of-service where a user may lose unsaved work if a malicious or malfunctioning local process triggers the flaw.
Technical details
An out-of-bounds read vulnerability (CWE-125) exists in Notepad++ prior to version 8.9.6.1. The issue resides in the handling of 'WM_COPYDATA' messages, specifically within the 'COPYDATA_FULL_CMDLINE' path in 'NppBigSwitch.cpp'. The application processes 'COPYDATASTRUCT.lpData' as an unbounded, NUL-terminated 'wchar_t*' string without validating the 'cbData' length field. By sending a malformed message with a large 'cbData' value and a buffer lacking a NUL terminator, a local process in the same interactive session can trigger an access violation (0xc0000005). This results in a reliable application crash. The vulnerability is fixed in version 8.9.6.1 by implementing proper bounds checking and exception handling during command-line string processing.
Affected products
- Notepad++ Notepad++ < 8.9.6.1
Timeline
- 2026-05-26: advisory: GitHub Security Advisory published by vendor
- 2026-06-26: disclosed: CVE published to NVD
- 2026-06-26: patched: Fix included in version 8.9.6.1