CVE-2022-3591: Vim Use After Free Vulnerability

CVE-2022-3591 Overview

CVE-2022-3591 is a Use After Free vulnerability discovered in the Vim text editor affecting versions prior to 9.0.0789. This memory corruption flaw exists in the buffer handling code and can be triggered when a dummy buffer ends up in a window during certain navigation operations. The vulnerability allows attackers to potentially execute arbitrary code or cause a denial of service when a user opens a maliciously crafted file or performs specific buffer operations.

Critical Impact

Successful exploitation of this Use After Free vulnerability could allow attackers to achieve arbitrary code execution with the privileges of the user running Vim, potentially leading to complete system compromise on affected systems.

Affected Products

• Vim versions prior to 9.0.0789
• vim:vim (all platforms)
• Systems with vulnerable Vim installations including Linux, macOS, and Windows

Discovery Timeline

• 2022-12-02 - CVE-2022-3591 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-3591

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a type of memory corruption vulnerability that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of Vim, the vulnerability manifests in the buffer handling logic within src/buffer.c. When navigating buffers using commands like DOBUF_GOTO or DOBUF_SPLIT, the code failed to properly validate whether the target buffer was a dummy buffer (indicated by the BF_DUMMY flag). Dummy buffers are internal structures not meant to be displayed in windows, and allowing navigation to them creates a condition where freed memory could be accessed.

The attack requires local access and user interaction, specifically the victim must open a malicious file or execute crafted Vim commands. Upon successful exploitation, attackers can achieve high impact to confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of CVE-2022-3591 lies in insufficient validation of buffer types during buffer navigation operations. The Vim codebase lacked proper checks to prevent navigation to dummy buffers, which are internal placeholder buffers not intended for display. When a user or malicious input triggers navigation to such a buffer, it can lead to accessing memory that has been freed or is in an invalid state, resulting in a Use After Free condition.

Attack Vector

This is a local attack vector vulnerability requiring user interaction. An attacker could craft a malicious Vim script or file that, when opened or executed by a victim, triggers buffer navigation commands targeting dummy buffers. The exploitation scenario typically involves:

1. Attacker creates a specially crafted file or Vim script
2. Victim opens the malicious file in Vim
3. The file triggers buffer operations that navigate to a dummy buffer
4. Use After Free condition is triggered, potentially allowing code execution

// Security patch from src/buffer.c - patch 9.0.0789
// Source: https://github.com/vim/vim/commit/8f3c3c6cd044e3b5bf08dbfa3b3f04bb3f711bad

    if ((flags & DOBUF_NOPOPUP) && bt_popup(buf) && !bt_terminal(buf))
	return OK;
#endif
+    if ((action == DOBUF_GOTO || action == DOBUF_SPLIT)
+					  && (buf->b_flags & BF_DUMMY))
+    {
+	// disallow navigating to the dummy buffer
+	semsg(_(e_buffer_nr_does_not_exist), count);
+	return FAIL;
+    }

#ifdef FEAT_GUI
    need_mouse_correct = TRUE;

Source: GitHub Commit Details

Detection Methods for CVE-2022-3591

Indicators of Compromise

• Unexpected Vim crashes or segmentation faults during buffer operations
• Abnormal memory access patterns in Vim process logs
• Presence of suspicious Vim script files attempting buffer manipulation commands
• Core dumps from Vim processes indicating memory corruption

Detection Strategies

• Monitor for Vim process crashes and analyze crash dumps for Use After Free patterns
• Implement file integrity monitoring on systems to detect malicious Vim scripts
• Use memory debugging tools like Valgrind or AddressSanitizer when running Vim in development environments
• Deploy endpoint detection solutions to identify exploitation attempts targeting Vim

Monitoring Recommendations

• Enable crash reporting for Vim processes to capture exploitation attempts
• Monitor system logs for repeated Vim crashes that may indicate active exploitation
• Implement SentinelOne's behavioral AI to detect anomalous process behavior following Vim execution
• Track Vim version deployments across enterprise environments to identify vulnerable installations

How to Mitigate CVE-2022-3591

Immediate Actions Required

• Update Vim to version 9.0.0789 or later immediately
• Review and audit any untrusted Vim scripts or configuration files
• Restrict execution of untrusted files in Vim on production systems
• Consider using Vim in sandbox environments when handling untrusted content

Patch Information

The vulnerability has been addressed in Vim version 9.0.0789 through commit 8f3c3c6cd044e3b5bf08dbfa3b3f04bb3f711bad. The fix adds proper validation to prevent navigation to dummy buffers by checking the BF_DUMMY flag before allowing DOBUF_GOTO or DOBUF_SPLIT actions. When a dummy buffer is detected, the operation now returns a failure with an appropriate error message instead of proceeding with the invalid navigation.

For detailed patch information, see the GitHub Commit Details and the Gentoo GLSA Advisory.

Workarounds

• Avoid opening untrusted files in Vim until the patch can be applied
• Run Vim with restricted mode (vim -Z) when editing files from untrusted sources
• Use containerized or sandboxed Vim environments for handling potentially malicious content
• Disable Vim modelines by adding set nomodeline to your .vimrc configuration

# Configuration example - Disable modelines for additional security
echo "set nomodeline" >> ~/.vimrc

# Verify Vim version to ensure patched version is installed
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-enhanced