CVE-2023-4750 Overview
CVE-2023-4750 is a Use After Free vulnerability affecting Vim, the popular text editor, in versions prior to 9.0.1857. This memory corruption flaw occurs specifically in the is_qf_win() function within the quickfix functionality, where a heap-use-after-free condition can be triggered. The vulnerability requires local access and user interaction, but successful exploitation can lead to arbitrary code execution with the privileges of the user running Vim.
Critical Impact
Attackers exploiting this vulnerability can achieve arbitrary code execution, potentially leading to full system compromise depending on the privileges of the Vim process. The vulnerability affects confidentiality, integrity, and availability of the system.
Affected Products
- Vim versions prior to 9.0.1857
- Fedora 37, 38, and 39
- Apple macOS (various versions)
Discovery Timeline
- 2023-09-04 - CVE-2023-4750 published to NVD
- 2024-11-21 - Last updated in NVD database
Technical Details for CVE-2023-4750
Vulnerability Analysis
This Use After Free vulnerability resides in Vim's quickfix window handling code. The flaw occurs when the is_qf_win() function in src/quickfix.c accesses a window's buffer without first validating that the buffer reference is still valid. During certain autocommand sequences, a buffer can be closed while windows still maintain references to it, creating a dangling pointer situation. When the quickfix-related code subsequently accesses this freed buffer memory, it results in a heap-use-after-free condition.
The vulnerability was discovered and reported through the Huntr bug bounty platform. The issue specifically affects how Vim handles buffer validity checks when iterating through windows in tab pages and when determining if a window is displaying quickfix content.
Root Cause
The root cause is inadequate buffer validity checking in two critical locations within the Vim codebase. In src/main.c, the code iterated through windows and checked only if wp->w_buffer == NULL, but failed to verify that the buffer was still valid using buf_valid(). Similarly, in src/quickfix.c, the is_qf_win() function accessed win->w_buffer properties without first confirming the buffer's validity. Autocommands can close buffers during certain operations, but the window structures may retain stale pointers to the freed buffer memory.
Attack Vector
The attack requires local access to the target system and user interaction to trigger. An attacker must craft a malicious Vim file or script that exploits the autocommand mechanism to trigger the use-after-free condition. When a user opens the malicious file or executes the crafted script, the vulnerability can be triggered during quickfix window operations. The attacker can potentially achieve arbitrary code execution by manipulating the freed heap memory before it is accessed.
The following patches demonstrate the fix applied to address this vulnerability:
Patch in src/main.c:
next_tp = tp->tp_next;
FOR_ALL_WINDOWS_IN_TAB(tp, wp)
{
- if (wp->w_buffer == NULL)
+ if (wp->w_buffer == NULL || !buf_valid(wp->w_buffer))
// Autocmd must have close the buffer already, skip.
continue;
buf = wp->w_buffer;
Source: GitHub Vim Commit Update
Patch in src/quickfix.c:
// set to NULL.
// A window displaying a location list buffer will have the w_llist_ref
// pointing to the location list.
- if (bt_quickfix(win->w_buffer))
+ if (buf_valid(win->w_buffer) && bt_quickfix(win->w_buffer))
if ((IS_QF_STACK(qi) && win->w_llist_ref == NULL)
|| (IS_LL_STACK(qi) && win->w_llist_ref == qi))
return TRUE;
Source: GitHub Vim Commit Update
Detection Methods for CVE-2023-4750
Indicators of Compromise
- Unexpected Vim crashes or segmentation faults during quickfix window operations
- Suspicious Vim script files or modelines that trigger autocommands manipulating buffers
- Abnormal memory access patterns in Vim processes detected by memory sanitizers
- Vim process spawning unexpected child processes or making unusual system calls
Detection Strategies
- Monitor for Vim processes exhibiting abnormal behavior such as crashes followed by unusual process execution
- Deploy memory safety tools (AddressSanitizer, Valgrind) in development and testing environments to detect use-after-free conditions
- Implement file integrity monitoring for Vim configuration files and scripts
- Use endpoint detection and response (EDR) solutions to monitor for exploit chains targeting text editors
Monitoring Recommendations
- Enable crash reporting and analysis for Vim processes across the organization
- Monitor system logs for patterns indicating exploitation attempts through Vim
- Track Vim version deployments and ensure timely updates to patched versions
- Implement SentinelOne's behavioral AI to detect post-exploitation activities that may follow successful memory corruption exploitation
How to Mitigate CVE-2023-4750
Immediate Actions Required
- Upgrade Vim to version 9.0.1857 or later immediately
- Apply vendor-provided security patches for Fedora 37, 38, and 39 systems
- Update macOS to the latest security release as referenced in Apple Support Article HT213984
- Audit systems for outdated Vim installations and prioritize remediation
Patch Information
The vulnerability has been addressed in Vim version 9.0.1857 through commit fc68299d436cf87453e432daa77b6d545df4d7ed. The fix adds proper buffer validity checks using the buf_valid() function before accessing buffer properties in both src/main.c and src/quickfix.c.
Patched packages are available through:
Workarounds
- Restrict execution of untrusted Vim scripts and modelines by adding set nomodeline to your vimrc configuration
- Avoid opening files from untrusted sources in Vim until patching is complete
- Consider using alternative text editors temporarily for handling untrusted content
- Implement strict application control policies to limit Vim execution contexts
# Configuration example - Add to ~/.vimrc to disable modelines
set nomodeline
set modelines=0
# Verify Vim version to ensure patched version is installed
vim --version | head -n 1
# Should show: VIM - Vi IMproved 9.0 (patch 1857 or higher)
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
