CVE-2023-40031 - Heap Buffer Write Overflow in Notepad++ Utf8_16_Read Convert Function Leading to Arbitrary Code Execution

Notepad++ is a widely used free and open-source source code editor that supports several programming languages. The program operates under the GPL License and works in a Microsoft Windows environment. Unfortunately, researchers have discovered a critical vulnerability present in versions 8.5.6 and prior of Notepad++, specifically in the Utf8_16_Read::convert function. This vulnerability may lead to heap buffer write overflow, ultimately resulting in arbitrary code execution. As of the time of publication, there are no known patches available in the existing versions of Notepad++.

Description of the Vulnerability

Heap buffer write overflow vulnerabilities occur when a program writes more data to a buffer located on the heap than the buffer can accommodate. This may subsequently lead to overwriting adjacent memory locations, causing memory corruption or crashes, and potentially resulting in arbitrary code execution.

In this case, the vulnerability is present in Notepad++'s Utf8_16_Read::convert function. This function is responsible for handling and converting text files that include different encodings, such as UTF-8 and UTF-16. When an attacker with malicious intent crafts a specially designed text file, it is possible to exploit this vulnerability and execute arbitrary code on the target machine.

Code Snippet of the Vulnerable Function

The following code snippet is taken from the vulnerable function in Notepad++ (source: Notepad++ GitHub repository):

size_t Utf8_16_Read::convert(char *_newBuf, size_t _newSize) const
{
    size_t ret = _newSize * 2;
    utf8_to_utf16((const utf8 *)_newBuf, utf16 *(&m_AllocatedBuffer));
    return ret;
}

Exploit Details

An attacker that has the ability to create a custom-crafted text file can potentially exploit this vulnerability. The exploit process proceeds as follows:

1. An attacker creates a specially designed text file that contains data that will trigger the Utf8_16_Read::convert function to overflow the heap buffer.

The victim opens the malicious text file using Notepad++.

3. As the text file is loaded into Notepad++ and the conversion process takes place, the heap buffer overflow is triggered, which may lead to memory corruption and potentially execute arbitrary code on the victim's machine.

Recommendations

As of the time of publication, there are no known patches available to fix this vulnerability in Notepad++. It is recommended that users take the following precautions until an official update is released:

Keep Notepad++ and all other installed software up-to-date.

3. Follow cybersecurity best practices, such as using strong passwords and keeping backups of essential files.

References

- Notepad++ GitHub Repository
- CVE - CVE-2023-40031
- CWE-122: Heap-based Buffer Overflow

Disclaimer

This document is provided for educational and informational purposes only. The author and publisher accept no responsibility for any damages or consequences that may result from the use or misuse of the information contained herein.

Timeline

Published on: 08/25/2023 20:15:00 UTC
Last modified on: 08/31/2023 18:11:00 UTC