CVE-2024-41957: Vim Use-After-Free Vulnerability

CVE-2024-41957 Overview

CVE-2024-41957 is a double free vulnerability in Vim, the widely-used open source command line text editor. The flaw exists in src/alloc.c at line 616 and occurs during window closure operations. When a window is closed, its associated tagstack data is cleared and freed. However, if the quickfix list belonging to that window points to the same tagstack data, Vim attempts to free the memory a second time, resulting in a double-free or use-after-free condition.

Critical Impact

This vulnerability can cause Vim to crash through a double-free memory corruption. While exploitation requires specific non-default flags, it represents a memory safety issue that could potentially be leveraged for more severe attacks in certain scenarios.

Affected Products

• Vim versions prior to v9.1.0647
• Systems running vulnerable Vim installations across Linux, macOS, and other Unix-like operating systems
• Downstream distributions packaging affected Vim versions

Discovery Timeline

• 2024-08-01 - CVE-2024-41957 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2024-41957

Vulnerability Analysis

This vulnerability is classified as CWE-415 (Double Free). The issue manifests when Vim processes window closure operations involving both tagstack and quickfix list data structures. The memory corruption occurs because two separate cleanup routines both attempt to deallocate the same memory region without proper coordination or tracking of memory ownership.

The vulnerability requires local access and user interaction to trigger, as specific non-default command line flags must be used. While the immediate impact is limited to application crashes, double-free vulnerabilities are historically dangerous as they can lead to heap corruption, which may be exploitable for arbitrary code execution under certain conditions.

Root Cause

The root cause lies in the window cleanup logic within src/window.c. When a window is freed, the win_free_lsize() function clears the tagstack entries by directly calling vim_free() on each entry's tagname and user_data fields. However, if a quickfix list shares pointers to the same tagstack data, subsequent cleanup of the quickfix list results in a second deallocation attempt on already-freed memory.

The fix introduces proper abstraction through the tagstack_clear_entry() function to ensure consistent and safe memory deallocation without double-free conditions.

Attack Vector

The attack vector is local, requiring an attacker to either have direct access to the system or trick a user into launching Vim with specific flags. The vulnerability cannot be exploited remotely without additional attack chains.

The exploitation scenario involves:

1. Executing Vim with non-default flags that create shared references between tagstack and quickfix list data
2. Performing operations that close a window while maintaining quickfix list references
3. The subsequent cleanup routines trigger the double-free condition

// Vulnerable code pattern (before patch) in src/window.c
    win_free_lsize(wp);

    for (i = 0; i < wp->w_tagstacklen; ++i)
    {
	vim_free(wp->w_tagstack[i].tagname);
	vim_free(wp->w_tagstack[i].user_data);
    }
    vim_free(wp->w_localdir);
    vim_free(wp->w_prevdir);

Source: GitHub Commit

// Patched code in src/window.c - uses centralized cleanup function
    win_free_lsize(wp);

    for (i = 0; i < wp->w_tagstacklen; ++i)
	tagstack_clear_entry(&wp->w_tagstack[i]);
    vim_free(wp->w_localdir);
    vim_free(wp->w_prevdir);

Source: GitHub Commit

Detection Methods for CVE-2024-41957

Indicators of Compromise

• Unexpected Vim crashes during window closure operations
• Segmentation faults or memory access violations in Vim processes
• Core dumps indicating double-free corruption in the heap
• Unusual Vim invocations with non-standard command line flags in process logs

Detection Strategies

• Monitor for Vim process crashes with memory corruption signatures using crash analysis tools
• Implement file integrity monitoring to detect unauthorized modifications to Vim binaries
• Review system logs for patterns of Vim crashes that could indicate exploitation attempts
• Deploy endpoint detection rules targeting double-free memory corruption patterns

Monitoring Recommendations

• Enable core dump collection for Vim processes to capture crash artifacts for forensic analysis
• Monitor process execution logs for Vim invocations with unusual or suspicious flag combinations
• Implement memory safety monitoring tools (such as AddressSanitizer in development environments) to detect memory corruption
• Track Vim version information across endpoints to identify vulnerable installations

How to Mitigate CVE-2024-41957

Immediate Actions Required

• Update Vim to version 9.1.0647 or later immediately
• Review and inventory all systems running Vim to identify vulnerable installations
• Apply vendor patches from distribution package managers (apt, yum, brew, etc.)
• Consider temporarily restricting Vim usage in sensitive environments until patching is complete

Patch Information

The vulnerability has been fixed in Vim patch v9.1.0647. The patch introduces the tagstack_clear_entry() function to properly handle tagstack memory deallocation, preventing the double-free condition. The fix ensures that memory is only freed once regardless of which cleanup path is taken.

Official patch resources:

• GitHub Security Advisory GHSA-f9cr-gv85-hcr4
• GitHub Commit 8a0bbe7b8aad6f8da28dee218c01bc8a0185a
• NetApp Security Advisory

Workarounds

• Avoid using non-default Vim flags in untrusted environments until patching is complete
• Restrict Vim execution to essential users and processes through access controls
• Consider using alternative text editors temporarily in high-security environments
• Implement process sandboxing for Vim to limit the impact of potential crashes or exploits

# Check current Vim version
vim --version | head -1

# Update Vim on Debian/Ubuntu systems
sudo apt update && sudo apt install vim

# Update Vim on RHEL/CentOS systems
sudo yum update vim

# Update Vim on macOS with Homebrew
brew upgrade vim

# Verify updated version (should be 9.1.0647 or later)
vim --version | grep -i "patch"