Cyber Resilience

CVE-2026-6539

Notepad-Plus-Plus Notepad\+\+ 8.9.3

Public PoC
Published
30 April 2026
Modified
01 May 2026
CVSS Score v4 4.6
Click a component to see what it means
Raw vectorCVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0019 9th percentile
Risk Priority 35 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-6539 is a medium-severity Use of Externally-Controlled Format String (CWE-134) vulnerability in Notepad-Plus-Plus Notepad\+\+. Its CVSS base score is 4.6 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

Notepad++ 8.9.3 contains a format string injection vulnerability in the Find Results panel handler that allows attackers to cause denial of service and information disclosure by crafting a malicious nativeLang.xml language pack file. Attackers can distribute a poisoned language pack…

more

through community channels that triggers format string interpretation when a user performs search operations, leading to access violations and potential leakage of stack or register contents.

CWE(s)
CWE-134

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2023-40166Same product: Notepad-Plus-Plus Notepad\+\+
CVE-2023-40036Same product: Notepad-Plus-Plus Notepad\+\+
CVE-2023-40031Same product: Notepad-Plus-Plus Notepad\+\+
CVE-2026-5525Same product: Notepad-Plus-Plus Notepad\+\+
CVE-2023-40164Same product: Notepad-Plus-Plus Notepad\+\+
CVE-2026-48770Same product: Notepad-Plus-Plus Notepad\+\+
CVE-2026-52884Same product: Notepad-Plus-Plus Notepad\+\+
CVE-2026-48800Same product: Notepad-Plus-Plus Notepad\+\+
CVE-2026-48778Same product: Notepad-Plus-Plus Notepad\+\+
CVE-2026-52885Same product: Notepad-Plus-Plus Notepad\+\+

Affected Assets

notepad-plus-plus
notepad\+\+
8.9.3

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and static analysis can discover format-string vulnerabilities before deployment.

SI-10 Information Input Validation good match

Input validation can reject or sanitize externally supplied format strings before they reach formatting functions.

SA-15 Development Process, Standards, and Tools partial match

Secure development standards and tools can mandate use of static format strings or safe formatting APIs.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly prevent external format strings via code review, static analysis, and safe APIs.

ID.RA-01 partial match
prevents

Vulnerability identification can discover existing format-string flaws but does not prevent their introduction.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development can detect format-string vulnerabilities before release.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC mandates input validation and safe API usage that can prevent externally-controlled format strings.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify safe formatting functions and ban uncontrolled format strings.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles discourage dangerous string-handling patterns that lead to format-string issues.

A.8.28 Secure coding partial match
prevents

Secure coding standards directly forbid the use of untrusted format strings and prescribe safe alternatives.

References