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CISA has included CVE-2025-15556 in its Known Exploited Vulnerabilities (KEV) catalog, emphasizing the ongoing exploitation of a significant code execution vulnerability in Notepad++, a commonly utilized open-source text editor favored by developers and IT experts.
Inserted on February 12, 2026, with a federal civilian executive branch (FCEB) patching deadline set for March 5, 2026, the vulnerability arises from the WinGUp updater’s inability to conduct integrity checks on downloaded code.
Cybercriminals can intercept or reroute update traffic, deceiving users into installing harmful payloads that execute arbitrary code with user-level permissions.
This vulnerability, categorized under CWE-494 (Download of Code Without Integrity Verification), presents substantial dangers in real-world breaches. Malicious actors could employ man-in-the-middle (MitM) strategies on unsecured networks to deliver altered installers, potentially introducing ransomware, malware droppers, or persistent backdoors.
While direct connections to ransomware operations remain uncertain, the ease of the vulnerability—requiring no authentication or user engagement beyond standard updates—renders it suitable for supply chain-style infiltrations.
Notepad++’s widespread use among Windows endpoints increases the risk, particularly in corporate settings where manual updates are prevalent.
| CVE ID | CVSS Score | Description |
|---|---|---|
| CVE-2025-15556 | TBD (NVD pending) | The Notepad++ WinGUp updater downloads code without integrity verification, permitting attackers to redirect traffic and run arbitrary code via a malicious installer. Versions preceding the patch are affected; impacts Windows users. |
Developers of Notepad++ have rectified the problem in version 8.8.9 and later, as explained in their official statement and community forum. The patch enforces cryptographic validation of update packages, thwarting interception efforts.
Nonetheless, users on affected versions (mainly 8.6 to 8.8.8) remain vulnerable if auto-updates are turned off—a common practice for stability.
CISA urges swift implementation of vendor updates, compliance with Binding Operational Directive (BOD) 22-01 for cloud-integrated services, or discontinuing the product if mitigations are not feasible.
Organizations should examine endpoints for outdated Notepad++ versions using tools such as Microsoft Defender or endpoint detection solutions, temporarily disable WinGUp, and enforce network segmentation to obstruct MitM vectors.
Activate update notifications and validate downloads against official SHA-256 hashes from notepad-plus-plus.org.
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