Vim is one of the most trusted and widely used text editors in the programming world. Its simplicity, speed, and power have earned it a devoted following. But even the best tools are not immune to flaws. Recently, a critical vulnerability—CVE-2025-24014—was discovered lurking in the internals of Vim versions before 9.1.1043. This post will guide you through what this bug is, why it’s dangerous, and how you can reproduce and defend against it.

What Is the Vulnerability?

When Vim runs in silent Ex mode (using the -s -e flags), it typically operates in the background, editing files without displaying anything on the screen. This is useful in scripts and automated setups.

However, a flaw was discovered: If you feed Vim certain binary characters as input while in silent mode, you can trigger a part of the Vim code responsible for handling graphical scrolling—even though there's no screen displayed. This function, meant for GUI versions of Vim or when the screen is up, tries to access a variable called ScreenLines.

Problem: In silent mode, ScreenLines isn't allocated (because there's no screen to display anything on). Attempting to use it leads to a Segmentation Fault, which crashes Vim. In some cases, this kind of bug could potentially be exploited for more serious attacks.

Here’s a simplified, pseudocode-level look

if (silent_ex_mode) {
    // However, some code path still processes input
    if (received_binary_input_triggers_scroll) {
        scroll_gui_screen();  // meant for GUI mode!
        // scroll_gui_screen calls screen_redraw()
        // screen_redraw() tries to access ScreenLines
        // But ScreenLines was never allocated!
        // Crash: Segmentation Fault
    }
}

When running

vim -s -e inputfile

And if inputfile contains certain malicious binary data, it can trigger this crash.

Here is an example Python snippet to generate an input file that might cause this issue

# Write binary data with control characters, potentially triggering the bug
with open("exploit.vim", "wb") as f:
    f.write(b"\x90\xAB\xCD\xEF\x00\x1b31mHello")  # Example binary payload

Then run

vim -s -e exploit.vim
If your Vim is vulnerable, it may crash with a segmentation fault.
Scripting environments that invoke Vim in silent mode- Systems relying on automated Vim tasks (for example, CI/CD pipelines)
Exploit DetailsWhile this particular bug mainly leads to a crash (denial of service), bugs that allow writing or reading out-of-bounds memory (like this one) are often the starting point for more serious attacks. At the very least, it’s a way to disrupt automated scripts using Vim.

Important: There is no publicly known way to gain code execution from this bug alone, but it’s a risk that cannot be ignored.
How Was It Fixed?The Vim maintainers patched the bug in version 9.1.1043 by ensuring that the scrolling function is never called in silent mode, and that unsafe access to uninitialized pointers like ScreenLines is prevented.Here’s the official fix on GitHub

- [Vim GitHub PR 14134 – fix segfault in silent ex mode (CVE-2025-24014)

Update notes

- Vim Patch 9.1.1043

Quote from official advisory

> "Fixed a segmentation fault when feeding certain binary input in -s -e (silent batch) mode. The scrolling/redraw code could attempt to use the uninitialized ScreenLines pointer."
> – Vim Release 9.1.1043 Notes

Simple: Update Vim!

vim --version

`

Or, download the latest Vim release and build from source.

References

- Vim CVE-2025-24014 Release Notes
- Vim GitHub Security Advisory
- Pull Request Fix


Keep your editor up to date, and stay savvy about even the simplest tools—sometimes, the quietest features hide the noisiest bugs!

Timeline

Published on: 01/20/2025 23:15:07 UTC
Last modified on: 01/21/2025 03:15:06 UTC