Vim, the widely-used open-source command-line text editor, has a vulnerability found in versions prior to 9.1.1043 that causes a segmentation fault when scrolling in silent Ex mode. This can potentially lead to undesirable behavior and crashes in certain configurations. This post will discuss the nature of this vulnerability, demonstrate a code snippet that displays the issue, and provide links to the original references and details on the exploit.
Vulnerability overview
The segmentation fault occurs in Vim when operating in silent Ex mode (-s -e). Normally, Vim doesn't display a screen in this mode and functions silently in batch mode. However, it's still possible to trigger the function responsible for handling scrolling in the graphical user interface (GUI) based Vim by providing certain binary characters as input. When this happens, the scrolling function may provoke a redraw, which accesses the 'ScreenLines' pointer - even though it isn't allocated, because there is no screen.
Exploit details
The root cause of this vulnerability lies in the fact that the code responsible for handling scrolling behavior attempts to redraw the screen when no screen is present. This triggers a segmentation fault since the 'ScreenLines' pointer has not been allocated.
Below is a code snippet demonstrating the vulnerability
#include <stdio.h>
#include <stdlib.h>
int main()
{
FILE *f = fopen("segfault.vim", "w");
fprintf(f, "%c:set scrollbind<80>bg", x1b);
fclose(f);
system("vim -s -e -S segfault.vim");
return ;
}
When you compile and execute this code, it will create a file called segfault.vim containing special binary characters that trigger the scrolling behavior. Running the Vim command will launch the text editor with silent Ex mode, and this will execute the Vimscript that forces the scrolling function, which in turn causes the segmentation fault.
Fix and references
This vulnerability has been patched in Vim 9.1.1043, so upgrading to this version or higher will prevent this vulnerability from being exploited. Here are the relevant references and patches:
1. Official Vim repository - Patch 9.1.1043
2. Vulnerability Details - CVE-2025-24014
3. Vim security update - Vim Announcement
Conclusion
In conclusion, it's crucial to always use the latest version of software to avoid exposing yourself to known vulnerabilities like the segmentation fault in Vim before 9.1.1043. By upgrading to a patched version, users can be confident in the security of their text editing environment. Stay current on security updates and remain vigilant to keep your systems safe in an ever-evolving threat landscape.
Timeline
Published on: 01/20/2025 23:15:07 UTC
Last modified on: 01/21/2025 03:15:06 UTC