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Notepad++ v8.9.9 Addresses Critical Privilege Escalation Vulnerabilities

Notepad++ v8.9.9 Addresses Critical Privilege Escalation Vulnerabilities

First seen 9 Nov 2026, 12:10 UTC • •
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ThreatCluster AI
ThreatCluster •November 9, 2026 at 12:10 UTC
  • •Version 8.9.9 fixes six vulnerabilities, including a critical buffer overflow.
  • •The most severe flaw could allow remote code execution via the mimeTools plugin.
  • •Users should update immediately to protect against potential exploitation.

Notepad++ has released version 8.9.9 to address six security vulnerabilities, including a critical heap-based buffer overflow in the SAML decoder of the mimeTools plugin. This flaw could allow attackers to execute arbitrary code by exploiting improperly handled Base64-encoded or DEFLATE-compressed SAML messages. Other vulnerabilities include a TOCTOU risk in UAC, heap disclosure, and various privilege escalation issues, all rated as medium risk. Users are urged to update promptly to mitigate these risks. The vulnerabilities currently do not have CVE identifiers assigned, but details are available on GitHub. The update also improves performance and includes several new features.

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Timeline

2026-11-09
Notepad++ v8.9.9 released
Version 8.9.9 was released to fix six vulnerabilities, including a critical heap overflow issue.
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Common questions

What vulnerabilities does version 8.9.9 fix?
It fixes a critical heap overflow and several medium-risk vulnerabilities related to privilege escalation and data handling.
How urgent is the update?
The update is urgent due to the critical nature of the heap overflow vulnerability that could allow remote code execution.
How can I update Notepad++?
Users can update via the built-in update checker or by using the command 'winget update Notepad++'.