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CVE-2025-15556

From Exploited flaws, HARD’s guide to the flaws being used in attacks · Checked
This article is about a flaw in Notepad++. For every flaw being used in attacks, see Exploited flaws.

CVE-2025-15556 is a security flaw in Notepad++. Attackers can run their own code on Notepad++. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 12 Feb 2026.[1]

Notepad++ is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 8.8.9 of notepad-plus-plus.

Description

CISA calls it a download of code without integrity check in Notepad++ Notepad++. In its words: “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.”[1]

The CVE record adds: “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.”[2]

The underlying weakness is CWE-494, in MITRE’s list of common software weaknesses.

It scores 7.5 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]

Affected versions

NVD’s record lists one fixed version: everything before it is affected.[2]

ProductFixed in
notepad-plus-plus8.8.9

Most families won’t have Notepad++; it’s for whoever looks after IT at work.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 12 Feb 2026, 9 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 5 Mar 2026 to fix it.[1]

FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 2%. That’s in the top 23% of the flaws it scores.[4]

CISA assesses it as not automatable: each attack takes some work.

CISA doesn’t say who was attacked, or how.

Fix

Notepad++ has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[1]

  1. Check whether you use it.Notepad++ is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
  2. Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 8.8.9 of notepad-plus-plus), or not in use. CISA gave US government agencies until 5 Mar 2026 to fix it.
  3. If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.

You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.

Timeline

DateEvent
The flaw is made public in the National Vulnerability Database, with a severity score of 7.5.[2]
CISA adds it to its catalog of flaws known to be used in attacks.[1]
CISA’s deadline for US government agencies to fix it.[1]
FIRST puts the odds of it being used in attacks in the next 30 days at 2%.[4]

See also

Similar flaws

  • CVE-2026-3502, TrueConf Client: download of code without integrity check ·
  • CVE-2022-40799, D-Link DNR-322L: download of code without integrity check ·
  • CVE-2021-44168, Fortinet FortiOS: arbitrary file download ·

Added the same day

  • CVE-2026-20700, Apple devices: multiple buffer overflow ·
  • CVE-2025-40536, SolarWinds Web Help Desk: security control bypass ·
  • CVE-2024-43468, Microsoft Configuration Manager: SQL injection ·

References

  1. ^ Cybersecurity and Infrastructure Security Agency. “Notepad++ Download of Code Without Integrity Check Vulnerability”. Known Exploited Vulnerabilities Catalog, added 12 Feb 2026.
  2. ^ National Institute of Standards and Technology. “CVE-2025-15556 Detail”. National Vulnerability Database, published 3 Feb 2026.
  3. ^ Notepad++. Advisories and fixes: notepad-plus-plus.org, community.notepad-plus-plus.org, notepad-plus-plus.org, notepad-plus-plus.org.
  4. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.017, percentile 77.8, 31 Oct 2026.
  5. CVE Program. “CVE-2025-15556”. The official CVE record.

This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.