CVE-2022-0392: Vim Heap-Based Buffer Overflow Vulnerability

CVE-2022-0392 Overview

CVE-2022-0392 is a heap-based buffer overflow vulnerability affecting Vim text editor versions prior to 8.2. The vulnerability occurs during bracketed paste operations in Ex mode, where improper memory allocation fails to account for the NUL terminator byte. This flaw allows an attacker to trigger an illegal memory access condition when a user opens a specially crafted file or pastes malicious content.

Critical Impact

This heap-based buffer overflow vulnerability can lead to arbitrary code execution with the privileges of the user running Vim, potentially allowing complete system compromise through a local attack vector requiring user interaction.

Affected Products

• Vim versions prior to 8.2.4218
• Apple macOS (addressed in security updates HT213444 and HT213488)
• Debian Linux 10.0

Discovery Timeline

• 2022-01-28 - CVE-2022-0392 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2022-0392

Vulnerability Analysis

The vulnerability exists in Vim's bracketed paste functionality within the src/edit.c source file. When processing paste operations in Ex mode, the code allocates a growing array buffer to store incoming data. The critical flaw occurs in the PASTE_EX case where the ga_grow() function is called with an insufficient size calculation that does not account for the terminating NUL byte that will be appended to the buffer.

This off-by-one error leads to a classic heap-based buffer overflow condition (CWE-122, CWE-787). When the buffer is filled and the NUL byte is written, it overflows into adjacent heap memory, causing memory corruption. Depending on heap layout and memory state, this can result in arbitrary code execution, application crash, or information disclosure.

Root Cause

The root cause is an improper boundary calculation in the memory growth operation. The original code called ga_grow(gap, idx) which allocated exactly idx bytes, but failed to reserve space for the NUL terminator that would subsequently be written. This represents a failure to properly validate buffer boundaries before memory write operations.

Attack Vector

Exploitation requires local access with user interaction - an attacker must convince a user to open a malicious file or paste specially crafted content while Vim is operating in Ex mode. The attacker can craft input that triggers the bracketed paste code path with specific buffer sizes to reliably overflow the heap boundary.

The attack flow involves:

1. Preparing a malicious file or clipboard content designed to trigger bracketed paste in Ex mode
2. User opens the file or pastes the content in Vim
3. The undersized buffer allocation is made
4. Data is written including the NUL terminator, overflowing heap memory
5. Heap corruption occurs, potentially leading to code execution

// Security patch in src/edit.c - patch 8.2.4218
// Source: https://github.com/vim/vim/commit/806d037671e133bd28a7864248763f643967973a

 		    break;
 
 		case PASTE_EX:
-		    if (gap != NULL && ga_grow(gap, idx) == OK)
+		    // add one for the NUL that is going to be appended
+		    if (gap != NULL && ga_grow(gap, idx + 1) == OK)
 		    {
 		mch_memmove((char *)gap->ga_data + gap->ga_len,
 					     buf, (size_t)idx);

Source: GitHub vim Commit Update

Detection Methods for CVE-2022-0392

Indicators of Compromise

• Unexpected Vim process crashes or segmentation faults during paste operations
• Abnormal memory allocation patterns in Vim processes
• Core dump files generated by Vim with heap corruption signatures
• Unusual files with embedded bracketed paste escape sequences opened by users

Detection Strategies

• Monitor for Vim process crashes with heap corruption indicators in core dumps
• Implement file integrity monitoring for Vim binary and configuration files
• Deploy endpoint detection rules that identify abnormal Vim memory behavior
• Use application sandboxing to contain potential exploitation attempts

Monitoring Recommendations

• Enable crash reporting and analyze Vim core dumps for heap overflow patterns
• Monitor system logs for repeated Vim crashes that may indicate exploitation attempts
• Track Vim version inventory across systems to identify unpatched installations
• Implement file scanning for potentially malicious files containing exploit payloads

How to Mitigate CVE-2022-0392

Immediate Actions Required

• Update Vim to version 8.2.4218 or later immediately
• Apply vendor security patches for Apple macOS (HT213444, HT213488) and Debian Linux
• Restrict execution of Vim in sensitive environments until patching is complete
• Educate users about the risks of opening untrusted files in Vim

Patch Information

The vulnerability is fixed in Vim version 8.2.4218 through commit 806d037671e133bd28a7864248763f643967973a. The fix adds one byte to the buffer growth calculation to accommodate the NUL terminator, preventing the heap overflow. Multiple downstream vendors have released patches:

• Vim: Fixed in version 8.2.4218 - see GitHub vim Commit Update
• Apple macOS: Addressed in Apple Security Update HT213444 and Apple Security Update HT213488
• Debian Linux: See Debian LTS Announcement November 2022 and Debian LTS Announcement March 2025
• Gentoo Linux: See Gentoo GLSA 2022-08-32

Workarounds

• Avoid using Ex mode for paste operations until the patch is applied
• Configure Vim to disable bracketed paste mode by adding set t_BE= to your vimrc
• Use alternative text editors for processing untrusted files
• Run Vim in a sandboxed environment to limit potential impact

# Configuration example - Disable bracketed paste in Vim
echo 'set t_BE=' >> ~/.vimrc

# Verify Vim version is patched
vim --version | head -1

# On Debian/Ubuntu, update Vim
sudo apt update && sudo apt upgrade vim

# On macOS, ensure system updates are applied
softwareupdate --list