CVE-2022-1154: Vim Use After Free Vulnerability

CVE-2022-1154 Overview

CVE-2022-1154 is a use after free vulnerability in the utf_ptr2char function in Vim, the popular text editor. This memory corruption flaw exists in versions prior to 8.2.4646 and can be triggered when processing maliciously crafted input, potentially leading to arbitrary code execution or denial of service on affected systems.

Critical Impact

This use after free vulnerability allows attackers to potentially execute arbitrary code with the privileges of the user running Vim, compromise system integrity, or cause application crashes through memory corruption.

Affected Products

• Vim versions prior to 8.2.4646
• Fedora 34 and 35
• Debian Linux 9.0 and 10.0
• Oracle Communications Cloud Native Core Network Exposure Function 22.1.1

Discovery Timeline

• March 30, 2022 - CVE-2022-1154 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-1154

Vulnerability Analysis

The vulnerability exists in Vim's regular expression engine, specifically in the src/regexp_bt.c file. The flaw occurs when processing buffer lines during regex operations involving marks. When getmark_buf() is called to retrieve a mark position, the function may free and reallocate the current buffer line, but the code continues to reference the old (now freed) memory location through rex.line and rex.input pointers.

This use after free condition (CWE-416) creates a dangerous situation where subsequent operations access memory that has been deallocated and potentially reused for other purposes. An attacker who can control input processed by Vim's regex engine could craft malicious content that triggers this condition, potentially achieving code execution or causing the application to crash.

Root Cause

The root cause lies in the regexp backtracking code's failure to refresh buffer line pointers after operations that may invalidate them. When getmark_buf() is invoked, it can trigger memory operations that free the current line buffer. The code did not account for this scenario and continued using stale pointers to the freed memory region.

Attack Vector

The attack requires local access and user interaction—a victim must open a specially crafted file or execute a Vim command that triggers the vulnerable regex pattern matching code path. While the attack complexity is low once the conditions are met, the local attack vector and user interaction requirement limit exposure compared to remotely exploitable vulnerabilities.

The following patch from commit b55986c52d4cd88a22d0b0b0e8a79547ba13e1d5 demonstrates the fix:

 		int	mark = OPERAND(scan)[0];
 		int	cmp = OPERAND(scan)[1];
 		pos_T	*pos;
+		size_t	col = REG_MULTI ? rex.input - rex.line : 0;
 
 		pos = getmark_buf(rex.reg_buf, mark, FALSE);
+
+		// Line may have been freed, get it again.
+		if (REG_MULTI)
+		{
+		    rex.line = reg_getline(rex.lnum);
+		    rex.input = rex.line + col;
+		}
+
 		if (pos == NULL		     // mark doesn't exist
 			|| pos->lnum <= 0)   // mark isn't set in reg_buf
 		{

Source: GitHub Commit b55986c5

The patch stores the current column position before calling getmark_buf(), then refreshes the rex.line pointer by calling reg_getline() and recalculates rex.input to point to the correct position in the newly fetched line buffer.

Detection Methods for CVE-2022-1154

Indicators of Compromise

• Unexpected Vim crashes or segmentation faults during file operations
• Anomalous memory access patterns in Vim processes when processing regex patterns
• Core dumps from Vim showing memory corruption signatures in regexp-related functions

Detection Strategies

• Monitor for Vim process crashes with memory corruption indicators in system logs
• Implement file integrity monitoring on systems where Vim is used to edit sensitive files
• Deploy endpoint detection solutions that can identify use after free exploitation attempts

Monitoring Recommendations

• Track Vim version deployments across your environment to identify vulnerable installations
• Monitor for suspicious files with complex regex patterns that could trigger the vulnerability
• Enable crash reporting and analysis for Vim processes to detect potential exploitation attempts

How to Mitigate CVE-2022-1154

Immediate Actions Required

• Update Vim to version 8.2.4646 or later immediately
• Apply vendor-provided patches from your Linux distribution's package manager
• Consider restricting Vim usage on sensitive systems until patching is complete
• Review any files from untrusted sources before opening in Vim

Patch Information

The vulnerability was fixed in Vim version 8.2.4646. The official patch is available through the GitHub commit b55986c52d4cd88a22d0b0b0e8a79547ba13e1d5. Multiple Linux distributions have released security updates:

• Fedora users should apply updates via the Fedora Package Announcements
• Debian users can reference the Debian LTS Security Advisories
• Gentoo users should consult GLSA 202208-32
• Oracle customers should review the Oracle Security Alert July 2022

Workarounds

• Use alternative text editors for processing untrusted files until Vim can be updated
• Avoid opening files from untrusted sources in vulnerable Vim versions
• Consider running Vim in restricted mode when editing potentially malicious content
• Implement application sandboxing to limit the impact of potential exploitation

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

# Update Vim on Fedora
sudo dnf update vim

# Update Vim on Gentoo
sudo emerge --sync && sudo emerge -av app-editors/vim

# Verify Vim version after update
vim --version | head -1