Vim is one of the most popular open-source text editors, loved by developers and system admins for its power and customizability. But even trusted tools like Vim can sometimes have serious bugs. In late 2023, a new vulnerability, *CVE-2023-48231*, was discovered in Vim that can lead to the application crashing (but, thankfully, not yet to more serious exploits).

In this article, we’ll break down what this vulnerability is all about, look at the code snipplet that shows the problem, discuss what the risks really are, and explain how you can protect yourself.

What is CVE-2023-48231?

CVE-2023-48231 is a vulnerability found in Vim. Specifically, it relates to how Vim handles windows (the interface, not the Microsoft operating system).

When you close a window in Vim, the application is supposed to properly clean up all the data structures associated with that window. Unfortunately, there’s a bug where Vim sometimes tries to access memory that has already been freed.

This is called a “use-after-free” bug and can cause the application to crash. In terms of security, use-after-free bugs are sometimes exploited by attackers to execute malicious code. However, so far, no one has figured out how to make this bug do more than just crash Vim.

The Technical Details (with Code Snippet)

Let’s look at a simplified code example to help explain the problem.

Imagine Vim’s window handling code looks like this (in simplified C-like code)

void close_window(Window *win) {
    free(win);   // Frees the memory for the window structure

    // ...some other logic...

    do_something(win);  // Oops! Tries to use the 'win' pointer that was just freed
}

In this example, after freeing the memory for the win window, the code tries to use it again. If that memory has already been released, this will almost certainly crash Vim.

In CVE-2023-48231, this sort of error existed in Vim’s actual source code, specifically relating to window management.

You can see the official fix in the Vim commit 25aabc2b, where the developers made sure that no freed memory is used after it’s released.

How Can This Be Exploited?

Currently, the only proven way to “exploit” this vulnerability is to cause Vim to crash. No one has shown that it’s possible to gain control over the system, steal information, or launch other attacks with this bug.

Open that file in a vulnerable version of Vim.

3. When the file triggers closing a window in a specific way, Vim tries to use the freed memory—and crashes.

Crashing the editor can be annoying but isn’t as dangerous as a remote code execution bug. Still, it’s best not to ignore this issue. Use-after-free bugs have sometimes been weaponized in other projects after creative research.

Is There a Workaround?

No. According to the official security advisory, there are no known workarounds for this bug. The best and only recommended action is to upgrade Vim.

Has It Been Fixed?

Yes. The Vim maintainers have fixed the bug in commit 25aabc2b. This fix is included in Vim version 9..2106 and newer. If you update to this version or later, you’re safe from this crash bug.

If your version is 9..2106 or higher, you’re safe.

2. Upgrade if needed: Visit the official Vim download page or use your system’s package manager to upgrade Vim.

Resources and References

- Official CVE Detail Page
- The Vulnerability Fix Commit on GitHub
- Vim Download Page

Conclusion

While CVE-2023-48231 isn’t a world-ending bug, it’s a good reminder to keep even your basic tools updated. For now, the vulnerability can crash your editor, but there’s always a chance a clever attacker could find a way to do more with it. To stay safe and avoid crashes, just update Vim to the latest version.

Timeline

Published on: 11/16/2023 23:15:08 UTC
Last modified on: 12/28/2023 17:39:29 UTC