CVE-2023-1170: Vim Buffer Overflow Vulnerability

CVE-2023-1170 Overview

CVE-2023-1170 is a heap-based buffer overflow vulnerability affecting the Vim text editor in versions prior to 9.0.1376. This memory corruption flaw occurs when performing a put operation in Visual block mode, leading to invalid memory access. Successful exploitation requires local access and user interaction but can result in application crashes, denial of service, and potential compromise of system integrity.

Critical Impact

This heap-based buffer overflow can cause Vim to crash or potentially allow attackers to corrupt memory, leading to denial of service and possible arbitrary code execution in the context of the affected user.

Affected Products

• Vim versions prior to 9.0.1376
• Linux distributions shipping vulnerable Vim packages (including Fedora)
• Any system with Vim installed from source prior to the security patch

Discovery Timeline

• 2023-03-03 - CVE-2023-1170 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-1170

Vulnerability Analysis

This vulnerability is classified as CWE-122 (Heap-based Buffer Overflow). The flaw exists in Vim's register handling code within src/register.c, specifically in the logic that processes trailing spaces during Visual block mode put operations. When a user performs a paste (put) operation in Visual block mode, the code responsible for inserting trailing spaces fails to properly validate the spaces variable before using it in memory operations.

The vulnerability allows invalid memory access because the condition checking for trailing spaces (if ((j < count - 1 || !shortline) && spaces)) does not adequately verify that the spaces value is positive. When spaces contains an unexpected value, the subsequent vim_memset() call can write to unintended memory locations on the heap, corrupting adjacent memory structures.

Root Cause

The root cause lies in insufficient validation of the spaces variable in the register handling code. The original conditional check && spaces was intended to verify that spaces needed to be inserted, but this check is inadequate because it only tests for non-zero values without ensuring the value is positive. A negative or corrupted spaces value could pass this check and cause the vim_memset() function to operate on an incorrect memory size, resulting in heap corruption.

Attack Vector

Exploitation of this vulnerability requires local access to the system and user interaction. An attacker would need to craft a malicious file or sequence of operations that, when opened and manipulated in Vim using Visual block mode paste operations, triggers the buffer overflow condition. The attack vector involves:

1. Preparing content that creates specific conditions in Vim's internal register state
2. Convincing a user to open the crafted content in Vim
3. Having the user perform a Visual block mode paste operation that triggers the vulnerable code path

// Security patch from src/register.c
// Source: https://github.com/vim/vim/commit/1c73b65229c25e3c1fd8824ba958f7cc4d604f9c

 		ptr += yanklen;
 
 		// insert block's trailing spaces only if there's text behind
-		if ((j < count - 1 || !shortline) && spaces)
+		if ((j < count - 1 || !shortline) && spaces > 0)
 		{
 		    vim_memset(ptr, ' ', (size_t)spaces);
 		    ptr += spaces;

The fix changes the condition from && spaces to && spaces > 0, ensuring that the vim_memset() operation only executes when the spaces variable contains a valid positive value.

Detection Methods for CVE-2023-1170

Indicators of Compromise

• Unexpected Vim crashes when performing paste operations in Visual block mode
• Core dumps or segmentation faults associated with the Vim process
• Memory corruption errors in system logs related to Vim execution
• Unusual process behavior or child processes spawned from Vim sessions

Detection Strategies

• Monitor for Vim process crashes, particularly segmentation faults or abort signals
• Implement file integrity monitoring on Vim binary and configuration files
• Deploy endpoint detection rules for anomalous memory access patterns in text editors
• Review system logs for repeated Vim crash events with similar patterns

Monitoring Recommendations

• Enable crash reporting and core dump collection for forensic analysis
• Configure SentinelOne to monitor for heap corruption indicators in Vim processes
• Set up alerts for multiple Vim crashes from the same user account in short time periods
• Monitor for suspicious files with unusual content being opened in Vim

How to Mitigate CVE-2023-1170

Immediate Actions Required

• Update Vim to version 9.0.1376 or later immediately
• Apply vendor-provided security patches from your Linux distribution
• Review systems for vulnerable Vim installations using package managers
• Consider temporarily restricting Vim usage on critical systems until patched

Patch Information

The vulnerability has been addressed in Vim version 9.0.1376. The security patch is available through the official Vim GitHub repository commit. Linux distributions including Fedora have released updated packages addressing this vulnerability, as noted in their package announcements.

Additional details about the vulnerability discovery and patch can be found on the Huntr bounty page.

Workarounds

• Avoid using Visual block mode paste operations until the patch is applied
• Consider using alternative text editors for critical operations on unpatched systems
• Implement application whitelisting to restrict Vim execution to trusted users
• Deploy additional memory protection mechanisms such as ASLR and heap hardening

# Check current Vim version
vim --version | head -1

# Update Vim on Fedora/RHEL-based systems
sudo dnf update vim-enhanced vim-common

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

# Build from source with the security patch
git clone https://github.com/vim/vim.git
cd vim
git checkout v9.0.1376
./configure && make && sudo make install