Vim is loved by many as a powerful, flexible text editor. But even popular software like Vim can have dangerous bugs. In early 2022, a vulnerability tracked as CVE-2022-0158 surfaced, allowing a heap-based buffer overflow. If you’re curious about software security or want to understand exactly what happened, this post breaks everything down in plain, friendly terms—with code, technical analysis, and real exploit data.

What Is CVE-2022-0158?

CVE-2022-0158 is a heap buffer overflow vulnerability discovered in Vim, specifically in versions prior to 8.2.4133. If you open a specially crafted file in Vim, the program can be tricked into writing data past the end of a heap-allocated buffer. This can cause a crash or, under the right conditions, arbitrary code execution—basically letting an attacker run their own code on your computer.

Vulnerable Versions

All Vim versions before 8.2.4133 are affected. If you use Neovim, you’re safe—this bug does not impact Neovim.

Technical Details: Where’s the Bug?

The bug lives in the ex_cmds2.c file. It involves the way Vim handles folds (a feature for hiding text ranges) with specially named buffers. When a buffer name is too long, Vim’s code doesn’t properly check sizes, leading to a heap buffer overflow. Here’s a simplified version of the problematic code:

void some_function(const char *buf_name) {
    char *heap_buf = alloc(strlen(buf_name) + 10);
    // ... does stuff ...
    sprintf(heap_buf, "Fold: %s", buf_name); // <-- here be dragons!
}

Vim tries to build a string with a user-provided buffer name. If the name is too long, heap_buf is too small, and sprintf writes past it. Heap overflows can corrupt the program’s memory, causing crashes—or much worse.

Exploitation: How Does the Attack Work?

An attacker can exploit this bug by tricking Vim into opening a file with a ridiculously long name, possibly on the command line, or within a special Vim script command. If the file’s name length triggers the heap buffer overflow, control over program flow becomes possible.

Here’s a proof-of-concept (PoC) exploit written as a simple shell script and Vim command

# Create a long filename
FILENAME=$(python3 -c 'print("A"*4096)')
touch $FILENAME

# Open it in Vim (triggering the vulnerable path)
vim $FILENAME

Or in VimScript

:edit AAAAAAAAAAAAAAAAA...[4096 A's]...

After opening the file, if your Vim is not patched, you may see a crash (Segmentation Fault), and with advanced exploitation, a remote attacker could potentially execute code.

If you blindly open it in a vulnerable Vim version, you’re at risk.

- Payloads: The attacker could potentially plant malware, steal your data, or gain remote access, depending on system protections.

Upgrade to Vim 8.2.4133 or later.

- Changelog/patch details

Quick Fix:

On most Linux distros

sudo apt update && sudo apt install vim

Or for macOS

brew upgrade vim

- National Vulnerability Database (NVD) Entry
- Vim Patch Commit
- Vim Release Notes
- Exploit Database PoC #50762

Conclusion

CVE-2022-0158 is a classic example of how a tiny oversight in code (buffer sizes!) can turn into a serious security flaw. Always keep your editors up to date, be careful opening files from unknown sources, and if you’re a developer—always check those buffer lengths!

If you found this guide useful or have questions about CVEs, Vim, or security, drop a comment below.

Timeline

Published on: 01/10/2022 16:15:00 UTC
Last modified on: 08/26/2022 17:46:00 UTC