Vim is a widely-used, open source command-line text editor. It’s popular among programmers and sysadmins for its power and extensibility. But like any software, it’s not immune to bugs and vulnerabilities. One of the recent security issues, tracked as CVE-2023-48237, deals with an integer overflow in Vim’s operator pending mode. Let’s walk through what happened, how someone might exploit this, and what you should do about it.
What Is CVE-2023-48237?
CVE-2023-48237 is a vulnerability in certain versions of Vim. It’s triggered if you attempt to "shift" (indent or de-indent) lines using operator pending mode with an extremely large value. If the number provided is high enough, the code handling the operation can overflow the integer value used internally.
What’s Operator Pending Mode?
In Vim, “operator pending mode” means you type an operator (like > to indent or < to de-indent) and then follow it with a movement (like pressing j for down, or typing a number for how many lines). Example: if you type 5>>, you’re asking Vim to indent five lines.
Users running affected Vim versions before 9..2112
- Users who interactively use operator pending commands with very large numbers (unlikely in most use)
No automatic exploitation—user interaction is required
*Impact is considered low*: There’s no known way to exploit this for code execution. At most, it could crash Vim or make it behave incorrectly.
Exploit Scenario (With Example)
As mentioned, exploitation requires a large number that wouldn’t happen under standard editing, but let’s see an example:
Here’s a (simplified) look at the affected code before patching
long amount = (long)count; // 'count' is user-supplied (e.g., '2147483648')
...
pos = startpos + amount;
If count is too large, amount overflows, leading to unexpected results.
Crash: Vim could exit with a segmentation fault or other error.
- Corruption: Data might not be shifted as intended (especially if the number overflows to a small or negative integer).
The issue is fixed in this commit
- 6bf131888
Summary of the fix:
The code now checks user-supplied values more carefully, preventing dangerous overflows.
If using an OS package manager (like apt, yum, or brew), update Vim via that system.
- If building from source, pull the latest stable version from Vim’s GitHub.
There’s *no workaround* if you keep using an older version; only upgrading will protect you from this bug.
References
- Vim Security Advisory
- CVE-2023-48237 in NIST Database
- Patch Commit 6bf131888
Conclusion
CVE-2023-48237 is a low-severity bug in Vim, exposing it to possible crashes when shifting lines with a comically large count. While practical exploitation is unlikely, best practice dictates you should always keep critical tools like Vim up to date. Just take a moment to update—safe editing is good editing!
Feel free to share this post to help keep the Vim community secure!
Timeline
Published on: 11/16/2023 23:15:09 UTC
Last modified on: 01/25/2024 21:33:53 UTC