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Actively exploited

CVE-2025-15556 Notepad++ Download of Code Without Integrity Check Vulnerability

Notepad++ when using the WinGUp updater, contains a download of code without integrity check vulnerability that could allow an attacker to intercept or redirect update traffic to download and execute an attacker-controlled installer. This could lead to arbitrary code execution with the privileges of the user.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch urgentlyCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 12 Feb 2026.
  • Rated High severity (CVSS 7.7, scored by Vendor).
  • It has been in the catalogue for 267 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

Notepad++ versions prior to 8.8.9, when using the WinGUp updater, contain an update integrity verification vulnerability where downloaded update metadata and installers are not cryptographically verified. An attacker able to intercept or redirect update traffic can cause the updater to download and execute an attacker-controlled installer, resulting in arbitrary code execution with the privileges of the user.

Affected Versions

ProductVersions
notepad-plus-plus notepad-plus-plusbefore 8.8.9

From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Notepad++. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated high, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 5 Mar 2026 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2025-15556
  3. CVE record: CVE-2025-15556
  4. FIRST EPSS
  5. notepad-plus-plus.org/news/clarification-security-incident/
  6. community.notepad-plus-plus.org/topic/27298/notepad-v8-8-9-vulnerability-fix
  7. notepad-plus-plus.org/news/hijacked-incident-info-update/
  8. github.com/notepad-plus-plus/notepad-plus-plus/commit/bcf2aa68ef414338d717e20e059459570ed6c5ab
  9. github.com/notepad-plus-plus/wingup/commit/ce0037549995ed0396cc363544d14b3425614fdb
  10. vulncheck.com/advisories/notepad-plus-plus-wingup-updater-lacks-update-integrity-verification