Security weaknesses in the widely used text editors Vim and GNU Emacs have been uncovered with the help of simple prompts given to the Claude AI assistant. These flaws could allow attackers to execute remote code merely by tricking users into opening a malicious file.
During the research, the AI assistant not only identified the vulnerabilities but also generated multiple proof-of-concept (PoC) exploits, refined them, and suggested potential fixes.
Vim and GNU Emacs are highly customizable text editors commonly used by developers and system administrators for coding, scripting, and terminal-based tasks. Vim, in particular, is deeply embedded in DevOps environments and comes pre-installed on most Linux distributions, embedded systems, and macOS.
Hung Nguyen, a cybersecurity researcher at Calif—a firm focused on AI red teaming and security engineering—discovered the Vim vulnerability by prompting Claude to locate a zero-day remote code execution (RCE) flaw triggered when opening a file.
Claude analyzed Vim’s source code and identified insufficient security checks, particularly in how modelines are handled. This allowed malicious code embedded within a file to execute as soon as the file is opened. A modeline is a snippet of text at the beginning of a file that instructs Vim on how to process it.
Even when such code was intended to run in a restricted sandbox, an additional flaw enabled attackers to bypass these protections and execute commands with the privileges of the current user.
The issue affects Vim versions 9.2.0271 and earlier and has not been assigned a CVE identifier. After Nguyen reported the vulnerability, Vim maintainers quickly released a fix in version 9.2.0272. They emphasized that simply opening a specially crafted file could trigger the exploit.
“An attacker who can deliver a crafted file to a victim achieves arbitrary command execution with the privileges of the user running Vim,” reads the bulletin.
GNU Emacs Vulnerability Linked to Git Integration
In contrast, the vulnerability affecting GNU Emacs remains unresolved, as its developers attribute the issue to Git rather than the editor itself.
The problem originates from Emacs’ version control integration (vc-git). When a file is opened, Emacs may trigger Git operations through vc-refresh-state. This process reads the .git/config file, where a malicious actor can define a core.fsmonitor program that executes arbitrary commands.
Nguyen demonstrated an attack scenario where a compressed archive—shared via email or cloud storage—contains a hidden .git directory with a manipulated configuration file pointing to a malicious script. Once the victim extracts the archive and opens a file, the payload executes silently under the default GNU Emacs setup.
While GNU Emacs maintainers argue that the issue lies within Git, the practical risk remains significant. The editor automatically invokes Git in untrusted directories without sanitizing potentially dangerous configurations, obtaining user consent, or enforcing sandbox protections.
To mitigate the threat, Nguyen recommended that GNU Emacs explicitly block the use of ‘core.fsmonitor’ in Git operations, preventing automatic execution of harmful scripts.
As no patch has yet been released for GNU Emacs, users are strongly advised to avoid opening files from untrusted or unknown sources.