CVE-2022-2124: Exploring the Buffer Over-read Vulnerability in Vim Prior to Version 8.2

Vim, the powerful and highly configurable text editor, has been a cornerstone of the UNIX and Linux world for a long time. Recently, a vulnerability identified as CVE-2022-2124 has been discovered in the source code of Vim versions prior to 8.2. This vulnerability is primarily due to a buffer over-read issue in the code that may lead to information disclosure or disruptions in the functionality of the system.

In this post, we will explore and discuss the details of this vulnerability, its potential impact, and how to mitigate against it.

Buffer Over-read Vulnerability in Vim

A critical buffer over-read vulnerability exists in the GitHub repository vim/vim prior to version 8.2. This particular issue is found within the handling of text properties in Vim's source code.

Essentially, when processing certain input, Vim fails to properly validate the length of the input data. As a result, an attacker can exploit this flaw by providing a specially-crafted input that causes Vim to read past the end of an allocated data buffer.

The vulnerable code snippet found within the src/textprop.c file of Vim's source code is shown below

void update_screenline(void)
{
    ...
    int buf_len = strlen((char *)buf) + 1;
    ...
    linebuf[buf_len - 1] = NUL;
    ...
}

The vulnerability resides in the usage of buf_len. Notice that the length of buf is calculated using strlen, which determines the length of a string up to a null-terminator byte. While this appears to be a safe operation, it can potentially allow an attacker to provide input that does not contain the null-terminator byte (NUL), thus causing strlen to keep counting beyond the boundaries of the actual buffer.

Furthermore, the line linebuf[buf_len - 1] = NUL; will erroneously set the null-terminator byte at a position that is out of the bounds of the buffer, resulting in a buffer over-read. Consequently, this may expose sensitive information or cause unexpected behavior that can potentially be exploited by an attacker.

You can refer to the original security advisory and report for this vulnerability in the following links:

- Vim Security Advisory
- NIST National Vulnerability Database (NVD) CVE-2022-2124

Mitigating the Vulnerability

To mitigate this issue, you should update your Vim installation to version 8.2 or later, which contains a patch addressing the vulnerability. You can download the latest version of Vim from the official Vim website at https://www.vim.org/download.php.

If updating Vim is not an option, you can configure your system to restrict access to sensitive data and monitor your system for any signs of unusual behavior. More specifically, ensure that the Vim editor does not have unnecessary access to sensitive files, services, or user accounts.

Conclusion

The CVE-2022-2124 vulnerability presents a critical security risk for users of the Vim text editor. It is crucial to understand the impact of this vulnerability and take the necessary steps in mitigating it. By updating to the latest version of Vim and maintaining due diligence in restricting access to sensitive information, you can protect your system from potential exploits related to this issue.

Timeline

Published on: 06/19/2022 10:15:00 UTC
Last modified on: 08/26/2022 18:04:00 UTC