CVE-2025-15556

Notepad++ versions prior to 8.8.9, when using the bundled WinGUp updater, download update metadata and installers without cryptographically verifying their integrity (CWE-494). An attacker who can intercept or redirect the updater's network traffic, such as through a man-in-the-middle position or a DNS hijack, can substitute an attacker-controlled installer that the updater then downloads and executes. Successful exploitation yields arbitrary code execution with the privileges of the user running Notepad++, with no attacker credentials or privileges required. Any Windows installation of Notepad++ with the auto-updater in use is affected, and because Notepad++ is one of the most widely used free Windows text editors the potentially exposed population is very large, although practical attacks require control of the victim's update path. CISA added CVE-2025-15556 to the Known Exploited Vulnerabilities catalog on 2026-02-12, and public reporting indicates the hijacked update mechanism was used to deliver targeted malware, confirming exploitation in the wild.

What to do: Upgrade to Notepad++ 8.8.9 or later, which adds integrity verification of downloaded updates; this is also the required remediation for federal agencies under CISA BOD 22-01 following the 2026-02-12 KEV listing. Until patched, restrict or monitor hosts' access to the Notepad++ update endpoint and check whether WinGUp recently executed any unexpected installers on systems of interest.