Overview
A heap-based buffer overflow vulnerability (CVE-2022-4141) has been discovered in the popular text editor Vim. Versions 9..0946 and below of Vim are affected by this vulnerability, which can result in a compromise of the user's system. This blog post describes the vulnerability, provides code snippets, and explains the exploit details. We will also provide links to original references and sources to help you stay informed about this critical issue.

Vulnerability Details
Heap-based buffer overflow vulnerabilities occur when a program writes more data to a fixed-size buffer than the buffer can hold. This can cause a buffer overflow, potentially resulting in unexpected behavior, application crashes, and, in some cases, the execution of arbitrary code by an attacker.

In this specific vulnerability, an attacker can trigger the buffer overflow by executing the "CTRL-W gf" command within Vim while using the expression found in the right-hand side (RHS) of the substitute command. This enables the attacker to execute arbitrary code on the victim's system, potentially leading to unauthorized access or data loss.

The following is a simple code snippet that demonstrates this vulnerability

" Example of vulnerable Vim script
:let vulnerable_var = "some_expression_here"
:%s/some_pattern/\=vulnerable_var/g | execute "normal! \<C-W>gf"

The code above first sets a variable named vulnerable_var using the let command. Then, it uses the substitute command, which searches for a pattern in the file and replaces it with an expression. The buffer overflow occurs when using the CTRL-W gf command to parse the expression in the RHS of the substitute command.

Exploit Details
In order to successfully exploit this vulnerability, an attacker may craft a malicious Vim file that includes the vulnerable code snippet as described above. Once the user opens the malicious file, the attacker's payload can be executed, potentially granting unauthorized access or executing additional malicious actions.

As a result, the attacker's payload can be executed on the victim's system.

Mitigation and Recommendations
The best way to mitigate this vulnerability is to update Vim to a version that contains the appropriate patch. Vim has released version 9..0947, which addresses this vulnerability. Users are encouraged to update to this version or later to protect themselves from this security issue.

Alternatively, users can disable the execution of arbitrary code from within Vim by adding the following line to their .vimrc configuration file:

set secure

Keep in mind that this setting may limit the functionality of some Vim plugins and scripts, so make sure to test and verify that your Vim environment functions as expected after applying this change.

Original References

Further information about this vulnerability can be found via the following sources

1. The official Vim repository on GitHub, where the vulnerability was patched in version 9..0947: https://github.com/vim/vim/releases/tag/v9..0947
2. The CVE-2022-4141 entry in the Common Vulnerabilities and Exposures (CVE) database: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-4141

Conclusion
CVE-2022-4141 is a critical heap-based buffer overflow vulnerability affecting Vim versions 9..0946 and below. By exploiting this vulnerability, an attacker can potentially compromise a user's system, executing arbitrary code and malicious payloads. Users are advised to update their Vim installations to the latest version or apply the appropriate mitigation steps mentioned earlier in this blog post. Additionally, monitoring the official Vim repository and the CVE database will help keep you informed about future vulnerabilities and patches.

Timeline

Published on: 11/25/2022 14:15:00 UTC
Last modified on: 06/12/2023 20:15:00 UTC