Vim is one of the most popular text editors used by programmers around the world. Its flexibility and power make it a great choice for editing source code and configuration files. However, like all software, Vim is not immune to bugs and security issues. Recently, a vulnerability was discovered—CVE-2025-22134—that affects how Vim handles buffers when visual mode is active and you use the :all command. Let’s break it down simply, look at how you can reproduce it, why it’s dangerous, and how the fix works.

What is CVE-2025-22134?

When you have visual mode enabled in Vim, you can select text and manipulate it. The :all command, on the other hand, opens all matching files into separate windows (like splits). The problem arises if you switch to other buffers using the :all command while visual mode is still active. In this situation, Vim does not properly exit visual mode, so it might try to access memory past the end of a line—causing a heap-buffer overflow.

In Simple Terms

- If you're in visual mode and run :all, Vim gets confused because it thinks you’re still selecting text.
- It might look for text in a place where nothing exists—outside the actual buffer in memory—which can cause it to crash or be exploited.

Who Found the Bug?

This vulnerability was discovered and reported by github user gandalf4a. Thanks to their efforts, the Vim team has patched the issue quickly.

How is this Dangerous?

Heap buffer overflows are serious. At best, they crash the application; at worst, an attacker can craft input that lets them run arbitrary code or leak sensitive information.

The impact here is “medium”—because the user must be in visual mode and use the :all command, it’s not immediately exploitable by opening a file. However, it’s possible for someone to trick you into executing a certain sequence, or for malicious plugins/scripts to trigger it.

Type :all and press Enter.

Vim may crash or behave unexpectedly. That’s the heap-buffer overflow.

Here’s a pseudo-code representation of what goes wrong

if (visual_mode_active) {
    // Switch buffer without ending visual mode
    //...
    line = get_line_from_another_buffer();
    if (cursor_position > line.length) {
        // Out of bounds: possible heap overflow
        access(line[cursor_position]); // Unsafe!
    }
}

The Fix: Patch 9.1.1003

The bug is fixed as of Vim Patch v9.1.1003, which:

1. Resets Visual Mode: Vim now makes sure to exit visual mode before switching windows or buffers via :all.
2. Buffer Line Check: Even when switching, Vim checks that the cursor is not trying to access beyond the end of a line.

Relevant Fix in the Patch

// Before switching buffers/windows
if (visual_mode_active) {
    end_visual_mode();
}

// Safe position check
if (current_position > buffer_line_length) {
    move_cursor_to_end_of_line();
}

If you want to see the full fix, you can check the official commit:
- Vim Patch v9.1.1003 Commit

References

- Vim Security Patch Notes
- CVE-2025-22134 on NVD
- Reporter’s Profile (gandalf4a)

What Should You Do?

Update Vim as Soon as Possible!
If you’re running Vim older than v9.1.1003, update immediately. Most Linux distributions should have this patch soon. You can also build the latest version from Vim’s GitHub.

Safe Habits:

Conclusion

CVE-2025-22134 is an example of how even a small oversight—like forgetting to exit visual mode—can lead to potentially serious bugs. Thanks again to gandalf4a for reporting the issue and to the Vim devs for fixing it quickly.

Always keep your editors and tools up to date to keep your system safe!

*This article is a unique and simplified explanation of CVE-2025-22134, exclusive for this post. Stay safe and happy coding!*

Timeline

Published on: 01/13/2025 21:15:14 UTC
Last modified on: 03/14/2025 10:15:16 UTC