CVE-2022-0413: Vim Use After Free Vulnerability

CVE-2022-0413 Overview

CVE-2022-0413 is a Use After Free vulnerability discovered in the Vim text editor prior to version 8.2. This memory corruption flaw occurs when the substitute command is used with a function call, leading to the application accessing memory that has already been freed. Successful exploitation of this vulnerability could allow an attacker to execute arbitrary code, cause denial of service, or potentially gain elevated privileges on the affected system.

Critical Impact

This Use After Free vulnerability in Vim could allow attackers to execute arbitrary code or cause system instability when a user opens a maliciously crafted file or executes specially crafted Vim commands.

Affected Products

• Vim versions prior to 8.2
• Fedora 34 and 35
• Debian Linux 9.0 and 10.0

Discovery Timeline

• 2022-01-30 - CVE-2022-0413 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-0413

Vulnerability Analysis

CVE-2022-0413 is classified as a Use After Free vulnerability (CWE-416), a type of memory corruption flaw that occurs when a program continues to use a pointer after the memory it references has been freed. In this case, the vulnerability manifests within Vim's substitute command functionality when combined with function calls.

When Vim executes a substitute operation that involves a function call, the program may improperly manage memory references. The memory allocated for the substitution string can be freed during the function call execution, but the pointer to this memory remains in use. Subsequent operations that reference this freed memory lead to undefined behavior, which attackers can potentially exploit.

The vulnerability requires local access and user interaction—an attacker must convince a victim to open a malicious file or execute specific Vim commands. Despite these prerequisites, successful exploitation can result in complete compromise of confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of this vulnerability lies in improper memory management within Vim's src/ex_cmds.c file. When performing substitution operations with embedded function calls, the substitution string pointer (sub) could reference memory that gets freed during function evaluation. The fix introduces a sub_copy variable to properly manage the lifetime of the substitution string, ensuring that memory references remain valid throughout the operation.

Attack Vector

The attack vector for CVE-2022-0413 requires local access to the system. An attacker would need to craft a malicious Vim script or file containing specially constructed substitute commands with function calls designed to trigger the Use After Free condition. The victim must then interact with this malicious content by opening the file in Vim or executing the crafted commands.

Potential attack scenarios include:

• Distributing malicious .vim configuration files
• Embedding harmful Vim modelines in seemingly innocent text files
• Tricking users into running malicious Vim scripts

// Security patch from src/ex_cmds.c - patch 8.2.4253
// Fix for using freed memory when substitute with function call
     int		save_do_all;		// remember user specified 'g' flag
     int		save_do_ask;		// remember user specified 'c' flag
     char_u	*pat = NULL, *sub = NULL;	// init for GCC
+    char_u	*sub_copy = NULL;
     int		delimiter;
     int		sublen;
     int		got_quit = FALSE;

Source: GitHub Commit 37f47958b8a2a44abc60614271d9537e7f14e51a

Detection Methods for CVE-2022-0413

Indicators of Compromise

• Unexpected Vim crashes or segmentation faults during substitute operations
• Abnormal memory access patterns in Vim processes
• Core dumps indicating memory corruption in ex_cmds.c related functions
• Unusual Vim script files containing complex substitute patterns with function calls

Detection Strategies

• Monitor for abnormal Vim process behavior including unexpected crashes or high memory consumption
• Implement file integrity monitoring for Vim configuration files (.vimrc, .vim/ directories)
• Deploy endpoint detection solutions capable of identifying memory corruption exploitation attempts
• Audit system logs for repeated Vim crashes that may indicate exploitation attempts

Monitoring Recommendations

• Enable core dump analysis to identify potential exploitation attempts targeting this vulnerability
• Monitor for suspicious file downloads that may contain malicious Vim scripts
• Implement SentinelOne's behavioral AI to detect anomalous process behavior associated with memory corruption exploits
• Track Vim version deployments across the environment to identify vulnerable installations

How to Mitigate CVE-2022-0413

Immediate Actions Required

• Update Vim to version 8.2.4253 or later immediately on all affected systems
• Review and audit any untrusted Vim scripts or configuration files before execution
• Implement application whitelisting to control which scripts can be executed
• Consider restricting Vim's ability to execute arbitrary scripts through modelines by setting set nomodeline in system-wide configuration

Patch Information

The vulnerability has been addressed in Vim patch 8.2.4253. The fix is available through the official Vim GitHub repository commit. Linux distributions have released security updates:

• Fedora: Updates available through standard package repositories (FEDORA-2022 announcements)
• Debian: Security patches released via Debian LTS announcements
• Gentoo: Addressed in GLSA 202208-32

Workarounds

• Avoid opening untrusted files in Vim until the patch is applied
• Disable modelines by adding set nomodeline to your .vimrc configuration
• Use restricted mode (vim -Z) when working with untrusted content
• Consider using alternative text editors for handling files from untrusted sources

# Configuration example - Add to system-wide vimrc
# Disable modelines to prevent automatic execution of embedded commands
echo "set nomodeline" >> /etc/vim/vimrc

# Verify Vim version to ensure patched version is installed
vim --version | head -1
# Should show VIM - Vi IMproved 8.2 (patch 4253 or higher)