CVE-2023-0049: Vim Buffer Overflow Vulnerability

CVE-2023-0049 Overview

CVE-2023-0049 is an out-of-bounds read vulnerability in the Vim text editor affecting versions prior to 9.0.1143. This memory safety issue occurs when processing malformed statusline values, potentially allowing an attacker to read beyond allocated memory boundaries. The vulnerability requires local access and user interaction to exploit, but could result in information disclosure or application crashes.

Critical Impact

Successful exploitation could lead to unauthorized access to sensitive memory contents, potential information disclosure, and application instability through memory corruption.

Affected Products

• Vim versions prior to 9.0.1143
• Fedora 36
• Fedora 37

Discovery Timeline

• 2023-01-04 - CVE-2023-0049 published to NVD
• 2025-01-17 - Last updated in NVD database

Technical Details for CVE-2023-0049

Vulnerability Analysis

This out-of-bounds read vulnerability (CWE-125) exists in Vim's statusline processing functionality. The flaw occurs when Vim attempts to parse a malformed statusline configuration value containing a trailing %0 sequence. In vulnerable versions, the parser continues reading memory after encountering a NUL character terminator, leading to invalid memory access beyond the intended buffer boundaries.

The vulnerability requires an attacker to craft a malicious Vim configuration or file that sets a specially crafted statusline value. When processed by an affected Vim instance, this triggers the out-of-bounds read condition. While the attack requires local access and user interaction (opening a malicious file or loading a malicious configuration), successful exploitation could expose sensitive memory contents or cause application crashes.

Root Cause

The root cause lies in insufficient boundary checking within Vim's statusline parsing code in src/buffer.c. When processing format specifiers in the statusline string, the parser failed to properly handle edge cases where a %0 sequence appears at the end of the string, resulting in the parser continuing past the NUL terminator. The fix adds an explicit check for the NUL character condition before advancing the string pointer.

Attack Vector

The vulnerability can be exploited through local access by convincing a user to open a maliciously crafted file or apply a malicious Vim configuration containing a specially formed statusline value. The attack requires user interaction, as the victim must actively load the malicious content into Vim. An attacker could potentially embed the malicious configuration in shared Vim configuration files, modelines within text files, or through other means that influence Vim's statusline processing.

// Security patch in src/buffer.c - adds NUL character check
// Source: https://github.com/vim/vim/commit/7b17eb4b063a234376c1ec909ee293e42cff290c

 #endif
 	if (vim_strchr(STL_ALL, *s) == NULL)
 	{
+	    if (*s == NUL)  // can happen with "%0"
+		break;
 	    s++;
 	    continue;
 	}

Source: GitHub Vim Commit Update

Detection Methods for CVE-2023-0049

Indicators of Compromise

• Unexpected Vim crashes or segmentation faults when opening certain files
• Vim configuration files containing unusual or obfuscated statusline values with %0 patterns
• Files containing suspicious modelines with malformed statusline directives
• Unusual memory access patterns or core dumps from Vim processes

Detection Strategies

• Monitor for Vim processes experiencing abnormal terminations or memory access violations
• Scan Vim configuration files (.vimrc, vimrc, modelines) for suspicious statusline patterns
• Implement file integrity monitoring on system-wide Vim configuration files
• Deploy endpoint detection to identify exploitation attempts through behavioral analysis

Monitoring Recommendations

• Enable core dump analysis for Vim processes to detect exploitation attempts
• Monitor system logs for segmentation faults or memory errors associated with Vim
• Implement alerting for modifications to Vim configuration files in sensitive directories
• Use SentinelOne's behavioral AI to detect anomalous Vim process behavior

How to Mitigate CVE-2023-0049

Immediate Actions Required

• Update Vim to version 9.0.1143 or later immediately
• Review and audit existing Vim configuration files for suspicious statusline values
• Consider disabling modeline processing with set nomodeline in system-wide Vim configuration
• Apply vendor-provided patches from your operating system distribution

Patch Information

The vulnerability has been addressed in Vim version 9.0.1143. The fix adds a boundary check for NUL character termination when parsing statusline format specifiers. The official patch is available through the GitHub Vim Commit with commit hash 7b17eb4b063a234376c1ec909ee293e42cff290c.

Distribution-specific patches are available from:

• Fedora Package Announcements
• Gentoo GLSA 2023-05-16
• Apple Security Update HT213670
• NetApp Security Advisory

Workarounds

• Disable modeline processing by adding set nomodeline to your Vim configuration
• Avoid opening untrusted files with Vim until the patch is applied
• Use alternative text editors for processing untrusted content temporarily
• Restrict Vim configuration modifications through file system permissions

# Configuration example - Disable modeline processing
# Add to /etc/vim/vimrc or ~/.vimrc
echo "set nomodeline" >> ~/.vimrc
echo "set modelines=0" >> ~/.vimrc