CVE-2022-0128: Vim Out-of-bounds Read Vulnerability

CVE-2022-0128 Overview

CVE-2022-0128 is an out-of-bounds read vulnerability affecting Vim, the popular text editor. This memory corruption flaw occurs when Vim reads one byte beyond the end of a line during command parsing, specifically when processing increment (++) and decrement (--) operators. The vulnerability can be triggered when a user opens a maliciously crafted file or executes specially crafted input, potentially leading to information disclosure, application crashes, or in some scenarios, arbitrary code execution.

Critical Impact

This out-of-bounds read vulnerability in Vim can allow attackers to cause denial of service or potentially execute arbitrary code when users interact with malicious files, affecting systems across Linux distributions and Apple macOS platforms.

Affected Products

• Vim (all versions prior to patch 8.2.4009)
• Apple Mac OS X 10.15.7 (multiple security update versions)
• Apple macOS (multiple versions including 11.x and 12.x series)

Discovery Timeline

• 2022-01-06 - CVE-2022-0128 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-0128

Vulnerability Analysis

The vulnerability exists in Vim's command parsing functionality within the ex_docmd.c source file. When parsing commands, Vim checks for increment (++) and decrement (--) operators by comparing consecutive characters. However, the original implementation failed to verify that the first character being checked was not a null terminator (NUL) before comparing it with the next character. This oversight allows an out-of-bounds read of one byte beyond the allocated buffer when processing the end of a line.

The flaw is classified as CWE-125 (Out-of-bounds Read), which occurs when software reads data past the end or before the beginning of an intended buffer. In this case, the missing bounds check enables reading beyond the legitimate memory boundaries of the command line being parsed.

Root Cause

The root cause is insufficient input validation in the command parsing logic. The vulnerable code directly compared p[0] with p[1] to detect consecutive + or - characters without first verifying that p[0] was not a null terminator. When p points to the end of a string (the null byte), the comparison p[0] == p[1] would read one byte past the string terminator, resulting in an out-of-bounds memory access.

Attack Vector

The attack requires local access and user interaction—specifically, a victim must open a maliciously crafted file or execute a crafted Vim command. An attacker could embed malicious content in a file that, when opened by Vim, triggers the vulnerable code path. While the local attack vector limits remote exploitation, the widespread use of Vim for editing configuration files and source code makes this a significant concern for development environments and server administration workflows.

// Vulnerable code in src/ex_docmd.c (before patch)
// Check for "++nr" and "--nr".
if (p == eap->cmd && p[0] == p[1] && (*p == '+' || *p == '-'))

// Fixed code in src/ex_docmd.c (patch 8.2.4009)
// Check for "++nr" and "--nr".
if (p == eap->cmd && p[0] != NUL && p[0] == p[1]
                                   && (*p == '+' || *p == '-'))

Source: GitHub Commit for Vim

Detection Methods for CVE-2022-0128

Indicators of Compromise

• Unexpected Vim crashes or segmentation faults when opening files
• Memory access violations logged in system logs related to Vim processes
• Unusual Vim behavior when parsing commands containing ++ or -- sequences

Detection Strategies

• Monitor for Vim process crashes and core dumps that indicate memory corruption
• Implement file integrity monitoring for Vim binaries to detect tampering
• Use memory sanitizer tools (AddressSanitizer, Valgrind) in development environments to detect out-of-bounds access
• Deploy endpoint detection tools to identify exploitation attempts targeting Vim

Monitoring Recommendations

• Configure system logging to capture Vim process errors and crashes
• Set up alerts for repeated Vim crashes from the same user or system
• Monitor for suspicious files with unusual encoding or content patterns that may be crafted to trigger the vulnerability

How to Mitigate CVE-2022-0128

Immediate Actions Required

• Update Vim to version 8.2.4009 or later immediately
• For Apple macOS users, apply the relevant security updates (HT213183, HT213256, or HT213343)
• Review and update Vim installations on all managed systems, including servers and developer workstations
• Consider temporarily restricting Vim usage on critical systems until patches are applied

Patch Information

The vulnerability was addressed in Vim patch 8.2.4009, which adds a null terminator check before comparing consecutive characters. The fix is available in the GitHub Commit for Vim. Apple has also released security updates addressing this vulnerability for macOS Monterey, macOS Big Sur, and macOS Catalina through security updates documented in Apple Support Article HT213183, Apple Support Article HT213256, and Apple Support Article HT213343. Gentoo users should reference Gentoo GLSA 202208-32 for distribution-specific guidance.

Workarounds

• Avoid opening untrusted files with Vim until patched
• Use alternative text editors for reviewing files from untrusted sources
• Enable operating system-level exploit mitigations such as ASLR and DEP
• Run Vim in sandboxed or containerized environments when handling potentially malicious content

# Check current Vim version
vim --version | head -n 2

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

# Update Vim on macOS via Homebrew
brew update && brew upgrade vim

# Verify patch level includes 8.2.4009 or higher
vim -c 'echo has("patch-8.2.4009")' -c 'quit'