Notepad++ 8.9.9 Update: Six Security Flaws Fixed, Including a WM_COPYDATA Bypass and Privilege Escalation, and How to Check Your Version
Notepad++ 8.9.9, released November 6, 2026, fixes six security flaws in the Windows editor and its MIME Tools plugin. Here is what each one does, what is confirmed, and how to check every PC.
Where Worldwide
On this page 7 sections
Notepad++ 8.9.9 came out on Friday, November 6, 2026, with fixes for six security flaws in the free Windows text editor and its bundled MIME Tools plugin. If your developers or IT staff run an older copy, other software on that PC can push it into opening files, pasting leaked memory into documents, slipping its own content into protected files, or, in one specific setup, running commands with administrator rights.
The advisories do not report any of the six being used in real attacks. Five of them need an attacker to already have code running on the machine. That still matters: Notepad++ lives on the PCs where admins edit server configs, hosts files and scripts, often with elevated rights, and those are the machines an intruder wants to reach next.
What the Notepad++ 8.9.9 update fixes
The official release notes list six fixes, each linked to a GitHub security advisory. None has a CVE number yet. The download page says "CVE ID not assigned yet" for each one.
| Flaw | What it lets an attacker do | Affected, per the advisory | Rating on GitHub |
|---|---|---|---|
| WM_COPYDATA sender authentication bypass (GHSA-pg39-63h5-cx35) | A low-integrity process (the restricted level Windows uses for sandboxed code) can make Notepad++ open any file Notepad++ can reach. If Notepad++ runs as administrator, a standard-user process can trigger file opens with elevated access | 8.9.7 and earlier | Moderate, CVSS 5.3 |
| WM_COPYDATA privilege escalation in isSenderTrusted() (GHSA-5jjv-2h6g-63p5) | The sender check can be fooled with a decoy Notepad++ window. With the NppExec plugin installed and loaded in an elevated Notepad++, a spoofed message ran a script at High (administrator) integrity | 8.9.8 | Moderate; the reporter suggested 7.0 High |
| UAC save race condition, TOCTOU (GHSA-w7wv-vg94-7pvp) | When you save a protected file and approve the UAC prompt, another process can swap the temporary file so its bytes get written instead of yours | 8.9.8 | Moderate, CVSS 6.6 |
| Heap disclosure in Paste Binary (GHSA-h5cv-65m7-x97v) | A process that writes to the clipboard can make Notepad++ paste extra memory contents into your document, which may include other document text and file paths | 8.9.8 and earlier | Moderate, CVSS 5.6 |
| Out-of-bounds access via NPPM_MENUCOMMAND (GHSA-j327-595g-jg4c) | A window message makes Notepad++ read past an empty list and hand the result to ShellExecute, the Windows function that launches programs. Control over that memory was not demonstrated | 8.9.8 and earlier | Moderate, CVSS 5.3 |
| Heap buffer overflow in MIME Tools SAML Decode (GHSA-554x-h7h6-gqfm) | A crafted SAML payload, decoded through Plugins, MIME Tools, SAML Decode, can write past allocated memory, causing a crash or potential code execution | MIME Tools 3.1 and earlier; fixed in 3.2 | High in the header; the advisory's impact field says "Critical (Potential Remote Code Execution / Denial of Service)" |
A note on versions, because they differ by flaw. The first advisory, published Tuesday, October 27, lists 8.9.7 and earlier as affected. The privilege escalation advisory was tested against the official 8.9.8 build, and its reporter suggests it may be an incomplete fix of that earlier issue. Whatever version you are on today, the fixed version is the same: 8.9.9.
The MIME Tools flaw is the one that does not need malware already on the PC. It does need a user to open a booby-trapped payload and run SAML Decode on it, which is a tool developers and identity admins actually use when troubleshooting single sign-on. The advisory notes MIME Tools is present in a default install.
What is confirmed and what is not
Confirmed by the Notepad++ project: six security fixes shipped in 8.9.9 on November 6, 2026, each with a published advisory, and the release notes and download page list all six.
Claimed by the researchers, not independently confirmed: the 7.0 High score for the privilege escalation is the reporter's suggestion, while GitHub lists it as Moderate. The MIME Tools code execution is described as "potential." The menu command flaw reached ShellExecute in testing, but the report says it did not show control over what gets run. A Clipboard History variant of the memory leak was not reproduced.
Not known: no CVE numbers have been assigned. None of the advisories reports real-world attacks. The GitHub "Patched versions" field on the five editor advisories reads "None", even though the release notes list all of them as fixed in 8.9.9. The release notes also do not name the MIME Tools version bundled with 8.9.9.
Why Notepad++ may not have offered the update yet
In the official community forum thread for the release, the maintainer wrote: "Auto-updater will be triggered in about 1 week, if no critical issue found in this release." So a PC that depends only on the built-in updater may still be on an older version this week. If you manage more than a handful of machines, push the update yourself rather than waiting for the prompt.
How to check your Notepad++ version and update this week
- Check the version: open Notepad++ and go to the ? menu, then About Notepad++. Anything below 8.9.9 needs updating.
- Download from the official site only: notepad-plus-plus.org. The installer is offered for x64, 32-bit and ARM64, and there is an x64 MSI for deployment through Intune or Group Policy.
- Verify the download: each package has a GPG signature, and SHA-256 hashes are published in a signed checksums file.
- Find portable copies: the portable and mini-portable builds do not show up in normal installed-software lists. Search admin PCs, shared drives and USB toolkits for notepad++.exe.
- Check MIME Tools: open Plugins, then Plugins Admin, then the Installed tab. The advisory lists 3.2 as the fixed version. If nobody uses it, remove it.
- Review NppExec: if it is installed on admin workstations, confirm someone still needs it.
- Stop running Notepad++ as administrator by habit: several of these flaws are worse when the editor is elevated. Open it elevated only for the one file that needs it.
Why this matters for a business network
A text editor sounds harmless, but think about where Notepad++ actually runs: the laptops of the people who hold your server passwords, edit firewall exports and paste API keys. Local flaws like these are the second step of an attack. Someone gets a foothold through a phishing email or a bad download, then looks for anything on the machine that will lend them more access. An elevated editor that trusts the wrong sender is exactly that.
The other problem is visibility. Many patch tools cover Windows and major browsers but skip free utilities, and portable copies are invisible to them entirely. We covered this gap in Who Is Patching the Software That Runs Your Business?. And as Updated Is Not the Same as Patched explains, the version number on the main app is not the whole story: here the MIME Tools plugin carries its own version and its own fix.
Notepad++ 8.9.9 questions people are asking
Is Notepad++ safe to use right now?
Yes, on version 8.9.9 with MIME Tools 3.2 or later, downloaded from the official site. Older versions carry the six flaws described above.
Do I need to update from Notepad++ 8.9.8?
Yes. Four of the six advisories list 8.9.8 as affected, and the MIME Tools fix comes with the new release.
Is the Notepad++ vulnerability being exploited?
None of the advisories reports exploitation in the wild. The researchers published proof-of-concept tests, so the details are public.
Does the Notepad++ privilege escalation work on a default install?
No. According to the advisory it needs the optional NppExec plugin loaded in an already elevated Notepad++, plus attacker code running on the same PC.
Will Notepad++ update itself?
Eventually. The maintainer said the auto-updater would be triggered about a week after release if no critical issue turned up. Updating manually is faster.
Does this affect Notepad++ on Mac or Linux?
The advisories describe the Windows desktop application and Windows mechanisms like window messages and UAC.
The bigger lesson
The tools your technical staff install themselves are part of your attack surface, and they need the same inventory and patch schedule as your servers. If nobody owns that list today, that is the gap to close, not just this one update.
See how we approach security hardening, or request a quote for a review of your systems.
Get security alerts like this by email, with our free checklist, at /security-alerts.
Sources: Notepad++ v8.9.9 release notes; Notepad++ v8.9.9 download page; Notepad++ community forum, release 8.9.9 thread; GHSA-pg39-63h5-cx35; GHSA-5jjv-2h6g-63p5; GHSA-w7wv-vg94-7pvp; GHSA-h5cv-65m7-x97v; GHSA-j327-595g-jg4c; MIME Tools GHSA-554x-h7h6-gqfm.
Have a question about this article?
Ask it here and we will answer you directly by email. Questions are private, never posted.
Security alerts by email
Hear about the next one first.
When attackers start using a flaw in software businesses run on, we email what it is, whether it touches you and what to do that week, with a round-up of our latest security writing. Free, one-click unsubscribe. You get the checklist straight away: 12 things to secure this week.
Want a result like this?
Security alerts, breaches and the technology a business runs on: what happened, who it affects and what to do.
Get a Tech QuoteKeep reading
Malicious OpenClaw Skills: Acronis Found 575 Fake AI Agent Add-Ons Pushing Malware to Windows and Mac, and What to Check This Week
Acronis researchers found 575 malicious OpenClaw skills posing as useful AI agent add-ons. Confirmed payloads...
Refrigeration Controller Hacks: CISA and FBI Warn Cold-Chain Businesses, What Is Confirmed and the Danfoss Firmware to Check
US agencies say attackers are targeting refrigeration and cold-chain controllers after two waves of store atta...
Binance Hack: $6.3 Billion Taken After Engineers' Laptops Were Compromised, What Is Confirmed and What to Check This Week
Attackers took about $6.3 billion from Binance on October 29. Binance's preliminary findings trace the theft t...
