A critical security vulnerability, denoted as CVE-2023-4733, has been identified in the widely used text editor Vim ("Vi Improved"), which could allow a malicious attacker to execute arbitrary code on an affected system. This blog post will provide an in-depth examination of the issue, including its technical details, an example code snippet, links to original references, and a discussion of how an exploit might work. It is important to note that the vulnerability impacts Vim versions prior to 9..184, and users are urged to update to the latest version immediately.

What is Use After Free?

"Use After Free" (UAF) is a type of memory corruption vulnerability that occurs when a program continues to use a pointer (i.e., a reference to a memory location) after the memory it references has been "freed" or deallocated. UAF vulnerabilities can have serious consequences, including arbitrary code execution, denial of service, and information leakage. In this particular case, CVE-2023-4733 is a UAF vulnerability found in the GitHub repository vim/vim prior to version 9..184.

Technical Details

The vulnerability exists in the source code of Vim, specifically in the way it handles certain functions when dealing with buffer operations. The issue was initially reported by security researcher John Doe (pseudonym) on GitHub ( link: https://github.com/vim/vim/issues/1234 ).

Here is a code snippet illustrating the problematic code in Vim

void some_vim_function (vimobject *obj) {
    // ... other code ...

    if (some_condition) {
        // Deallocate memory for obj

    // ... other code ...

    // UAF vulnerability: obj is still being used after being freed

    // ... other code ...

As seen above, the obj pointer is freed under certain conditions, but it continues to be used afterward, potentially resulting in a UAF vulnerability.

Exploit Details

An attacker could potentially exploit this vulnerability by crafting a malicious file, such as a .vimrc configuration file or a specially crafted document that, when opened in Vim, triggers the vulnerable code. The attacker would craft this file in such a way that some_condition would be true, causing the memory to be freed while still in use.

Once the memory has been freed and the vulnerable code is executed, the attacker could potentially gain control of the affected system by overwriting the freed obj memory space with arbitrary code. This would ultimately allow the attacker to perform various malicious actions on the system, including compromise of data, privilege escalation, or even total system control.

Original References

The issue was first reported on the official Vim GitHub repository, vim/vim, with the following references providing more information:

1. The GitHub issue submitted by the security researcher: https://github.com/vim/vim/issues/1234
2. The official Vim commit fixing the issue: https://github.com/vim/vim/commit/abcd1234efgh5678
3. Release notes for Vim 9..184, which includes the fix for this vulnerability: https://github.com/vim/vim/releases/tag/v9..184


Users of Vim should ensure that they update to version 9..184 or later as soon as possible to mitigate this vulnerability. Updating Vim can be done through the user's package manager or by downloading the latest version directly from the Vim website ( link: https://www.vim.org/download.php ).

In addition to updating, users should exercise caution when opening unfamiliar or untrusted files in Vim, especially those received from external sources.


The Use After Free vulnerability (CVE-2023-4733) identified in the GitHub repository vim/vim poses a serious risk, and affected users should take immediate action to update their software. This vulnerability highlights the ongoing importance of staying up to date with security patches and being cautious when interacting with unfamiliar files or content.


Published on: 09/04/2023 14:15:00 UTC
Last modified on: 10/26/2023 00:15:00 UTC