CVE-2025-27423: The Critical Vulnerability in Vim's tar.vim Plugin and How it was Fixed

Vim is a widely used open-source command-line text editor that is highly customizable and extensible. One of the bundled plugins in Vim is the tar.vim plugin, which allows users to edit and view (compressed or uncompressed) tar files directly from the editor. However, a critical vulnerability (CVE-2025-27423) was discovered in this plugin, affecting Vim versions 9.1.0858 and later. In this post, we will discuss the details of the vulnerability, how it can be exploited, and the steps taken to fix it.

The Vulnerability

The vulnerability was discovered in the tar.vim plugin, which allows the execution of shell commands via specially crafted tar archives. This is because the plugin uses the ":read" ex command line to append below the cursor position. Unfortunately, the input from the tar archive used in the ":read" ex command line was not sanitized, allowing for the possibility of code execution.

Here is a code snippet illustrating the issue

" Read the tarfile
for i in range(10)
  execute "silent read !" .shellescape(tar'{tarfile}'.format(i))
endfor

The problem arises because the shellescape() function does not properly sanitize the input, potentially allowing the execution of unintended shell commands. The exploit, however, depends on the shell being used ('shell' option, which is set using $SHELL).

Exploit Details

To exploit the vulnerability, a malicious actor could create a specially crafted tar archive with a file containing shell commands. When this archive is opened in Vim using the tar.vim plugin, the commands would be executed automatically, without any user interaction.

Here's an example of a malicious tar archive

$ tar cf malicious.tar --directory /tmp 'filename;touch exploittestfile'

When opened in Vim with the tar.vim plugin active, the shell command touch exploittestfile will be executed, creating a file named 'exploittestfile' in the current directory.

For a more detailed explanation of the vulnerability and the exploit, you can refer to the following original references:

1. Vim-dev mailing list announcement
2. GitHub issue discussion

The Fix and Patch

The issue was fixed in Vim patch v9.1.1164, which was released after the vulnerability was discovered and reported. The patch ensures that the input from the tar archive is sanitized before being passed to the ":read" ex command line, effectively preventing the possibility for code execution via malicious shell commands in tar archives.

Here's the fixed code snippet with proper input sanitization

" Read the tarfile
for i in range(10)
  let safe_input = fnameescape(tar'{tarfile}'.format(i))
  execute "silent read !" . safe_input
endfor

To protect Vim installations from this vulnerability, users should update to the latest version of Vim, which includes the patch v9.1.1164, or manually apply the patch for earlier versions from the following link: Vim patch v9.1.1164

Conclusion

As software developers and users, we must be continually vigilant to the risks posed by vulnerabilities in the software we use daily. CVE-2025-27423 serves as a reminder of how even widely used and respected open-source projects like Vim can contain critical security issues. Thankfully, Vim's active community and developers quickly worked together to fix the issue and protect the users. It is essential to regularly update your software and stay informed about security issues to protect yourself and your organization from potential exploits.

Timeline

Published on: 03/03/2025 17:15:15 UTC
Last modified on: 05/02/2025 23:15:16 UTC