oss-security - [vim-security] Arbitrary Code Execution via Python Omni-Completion in Vim

Follow @Openwall on Twitter for new release announcements and other news

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <aiHrf7gTq2gMr2Wy@256bit.org>
Date: Thu, 4 Jun 2026 23:17:51 +0200
From: Christian Brabandt <cb@...bit.org>
To: oss-security@...ts.openwall.com
Subject: [vim-security] Arbitrary Code Execution via Python Omni-Completion
 in Vim < 9.2.597

Arbitrary Code Execution via Python Omni-Completion in Vim < 9.2.597
====================================================================

Date: 2026-06-04
Severity: Medium
CVE: *requested, not yet assigned*
CWE: Improper Control of Generation of Code (CWE-94)

## Summary

Vim's Python omni-completion executes reconstructed function and class
definitions from the current buffer with `exec()` as part of populating
the completion dictionary. Python evaluates function default values,
parameter annotations, and class base expressions at definition time,
so a hostile buffer can execute attacker-controlled Python expressions
during omni-completion. The existing `g:pythoncomplete_allow_import`
mitigation (GHSA-52mc-rq6p-rc7c) does not cover this path, because the
attacker-controlled code is not a harvested `import`/`from` statement.

## Description

In `runtime/autoload/python3complete.vim` (and the legacy
`pythoncomplete.vim`), the omni-completion entry point calls
`exec(src, self.compldict)` on source reconstructed from the parsed
buffer. The reconstructed source includes function definitions whose
parameter lists are joined verbatim from tokens harvested by the
internal `_parenparse()` helper, which preserves default expressions
and annotations as written in the buffer. The same applies to class
base lists. When `exec()` runs the reconstructed `def` and `class`
statements, Python evaluates those expressions.

## Impact

An attacker who can convince a user to open or edit a hostile Python
buffer and trigger Python omni-completion (CTRL-X CTRL-O, or a plugin
that invokes the completion function) can execute Python code in the
user's Vim process. The code runs with the user's privileges.

Vim built without `+python3` and `+python` is not affected. Triggering
omni-completion in the hostile buffer is required; opening the file
alone is not sufficient.

## Acknowledgements

The Vim project would like to thank github user DavidCarliez for
reporting and analyzing the issue.

## References

The issue has been fixed as of Vim patch [v9.2.597](https://github.com/vim/vim/releases/tag/v9.2.0597).
- [Commit](https://github.com/vim/vim/commit/c8c63673bc4253212820626aeeb75999d9a539d2)
- [Github Security Advisory](https://github.com/vim/vim/security/advisories/GHSA-65p9-mwwx-7468)
- [Github Security Advisory GHSA-52mc-rq6p-rc7c](https://github.com/vim/vim/security/advisories/GHSA-52mc-rq6p-rc7c)
  (prior mitigation for the same surface)

Thanks,
Christian
-- 
Erfolg ist die Kunst, Fehler zu machen, die kein anderer bemerkt.
		-- Martin Jente

Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.