CVE-2026-4744: Notepad3 Buffer Overflow Vulnerability

CVE-2026-4744 Overview

An out-of-bounds read vulnerability has been identified in rizonesoft Notepad3, specifically within the scintilla/oniguruma/src modules. This vulnerability is associated with program files regcomp.c and affects Notepad3 versions prior to 6.25.714.1. The flaw occurs due to improper boundary checks during memory read operations, potentially allowing attackers to access sensitive memory regions beyond allocated buffers.

Critical Impact

This out-of-bounds read vulnerability could allow an attacker to read sensitive data from adjacent memory locations, potentially leading to information disclosure, application crash, or enabling further exploitation chains including code execution when combined with other vulnerabilities.

Affected Products

• Notepad3 versions before 6.25.714.1
• scintilla/oniguruma regex library components
• Systems running vulnerable Notepad3 installations with regex processing functionality

Discovery Timeline

• 2026-03-24 - CVE-2026-4744 published to NVD
• 2026-03-24 - Last updated in NVD database

Technical Details for CVE-2026-4744

Vulnerability Analysis

This vulnerability is classified as CWE-125 (Out-of-bounds Read), a memory safety issue that occurs when software reads data past the end or before the beginning of an intended buffer. In the context of Notepad3, the vulnerability resides in the Oniguruma regular expression library integration within the Scintilla editor component.

The vulnerability requires local access and user interaction—specifically, a user must open or process a maliciously crafted file or input that triggers the regex engine. When exploited, the flaw can read memory outside the designated buffer boundaries, potentially exposing sensitive information stored in adjacent memory regions.

The local attack vector combined with user interaction requirements means an attacker would typically need to social engineer a victim into opening a specially crafted document. Despite these prerequisites, the potential impact across confidentiality, integrity, and availability is significant.

Root Cause

The root cause of this vulnerability lies in insufficient bounds checking within the regcomp.c file, which handles regular expression compilation in the Oniguruma library. During the regex pattern compilation process, the code fails to properly validate memory access boundaries, allowing read operations to extend beyond the allocated buffer space. This is a common issue in C-based regex implementations where manual memory management is required.

Attack Vector

The attack requires local access to the target system. An attacker must craft a malicious file or input containing a specially designed regex pattern that, when processed by Notepad3's Oniguruma-based regex engine, triggers the out-of-bounds read condition. This typically involves:

1. Creating a document or search pattern with malformed regex syntax designed to trigger edge cases in regcomp.c
2. Enticing a victim to open the malicious file in Notepad3 or use the crafted pattern in a search/replace operation
3. The vulnerable code path reads beyond allocated buffer boundaries during regex compilation
4. Sensitive memory contents may be exposed or the application may crash

The vulnerability mechanism involves improper validation of index or offset values during regex pattern processing. When the Oniguruma regex compiler encounters certain malformed patterns, it may calculate incorrect buffer offsets, leading to out-of-bounds memory access. For detailed technical information, see the GitHub Pull Request #5392 which contains the fix.

Detection Methods for CVE-2026-4744

Indicators of Compromise

• Unexpected Notepad3 application crashes during file opening or search operations
• Memory access violations or segmentation faults in Notepad3 process logs
• Abnormal memory read patterns detected in endpoint monitoring tools
• Presence of suspicious files with unusual regex patterns targeting Oniguruma library

Detection Strategies

• Monitor for Notepad3 crashes and analyze crash dumps for signs of out-of-bounds memory access
• Implement file scanning to detect documents containing potential regex-based exploit patterns
• Use memory protection tools to detect and alert on out-of-bounds read attempts
• Deploy endpoint detection solutions that can identify exploitation attempts targeting text editors

Monitoring Recommendations

• Enable crash dump collection for Notepad3 to aid in forensic analysis of potential exploitation attempts
• Monitor for unusual process behavior patterns associated with Notepad3, particularly during file operations
• Implement application-level logging to track regex pattern processing activities
• Review endpoint telemetry for anomalies in memory access patterns from Notepad3 processes

How to Mitigate CVE-2026-4744

Immediate Actions Required

• Update Notepad3 to version 6.25.714.1 or later immediately
• Avoid opening untrusted documents or files in vulnerable Notepad3 versions
• Consider using alternative text editors until the patch can be applied
• Restrict execution of Notepad3 to trusted, verified files only

Patch Information

rizonesoft has addressed this vulnerability in Notepad3 version 6.25.714.1. The fix involves implementing proper bounds checking in the regcomp.c file within the Oniguruma regex library components. Users should update to this version or later to remediate the vulnerability. The patch details can be reviewed in GitHub Pull Request #5392.

Workarounds

• Disable or avoid using regex-based search/replace functionality until the patch is applied
• Use alternative text editors for processing untrusted files
• Implement application allowlisting to control which files can be opened by Notepad3
• Deploy endpoint protection solutions to detect and block exploitation attempts

# Verify Notepad3 version on Windows systems
# Navigate to Notepad3 installation directory and check version
dir "C:\Program Files\Notepad3\Notepad3.exe" /q

# Alternatively, check via PowerShell
Get-ItemProperty "C:\Program Files\Notepad3\Notepad3.exe" | Select-Object VersionInfo