CVE-2022-1629: Vim Buffer Over-read Vulnerability

CVE-2022-1629 Overview

CVE-2022-1629 is a buffer over-read vulnerability in the find_next_quote function in the Vim text editor prior to version 8.2.4925. This security flaw occurs when processing text with trailing backslash escape sequences, potentially allowing an attacker to read past the end of a line buffer. The vulnerability can result in software crashes, memory modification, and potentially remote code execution when a user opens a specially crafted file.

Critical Impact

This buffer over-read vulnerability in Vim can crash the application, modify memory contents, and potentially enable remote code execution through maliciously crafted files.

Affected Products

• Vim versions prior to 8.2.4925
• Fedora 34 and 35
• Apple macOS (multiple versions)

Discovery Timeline

• 2022-05-10 - CVE-2022-1629 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-1629

Vulnerability Analysis

The vulnerability resides in the find_next_quote function within Vim's text object handling code (src/textobject.c). When processing quoted strings with escape characters, the function fails to properly validate that the buffer has not been exhausted after incrementing past an escape sequence. Specifically, when a trailing backslash is encountered at the end of a line, the function increments the column index but continues processing without checking if the new position is beyond the line's null terminator.

This out-of-bounds read condition (CWE-125, CWE-126) allows reading memory beyond the intended buffer boundaries. The local attack vector requires user interaction—the victim must open a maliciously crafted file containing the exploit payload. Successfully exploiting this vulnerability can lead to information disclosure from adjacent memory regions, application crashes due to accessing invalid memory, or potentially arbitrary code execution if the attacker can control the over-read data in a meaningful way.

Root Cause

The root cause is insufficient boundary checking in the find_next_quote function when handling escape characters. After incrementing the column index to skip past an escaped character, the code does not verify that the new position is still within the valid bounds of the line buffer before continuing to process additional characters. This oversight allows the function to read beyond the null terminator that marks the end of the line.

Attack Vector

The attack requires local access and user interaction. An attacker must craft a malicious file containing specially formatted text with a trailing backslash escape sequence. When a victim opens this file in Vim and performs certain text object operations (such as selecting quoted text), the vulnerable find_next_quote function is triggered, causing the buffer over-read. The attacker could potentially leverage this to leak sensitive information from memory or cause denial of service through application crashes.

// Security patch from src/textobject.c
// Source: https://github.com/vim/vim/commit/53a70289c2712808e6d4e88927e03cac01b470dd
 	if (c == NUL)
 	    return -1;
 	else if (escape != NULL && vim_strchr(escape, c))
+	{
 	    ++col;
+	    if (line[col] == NUL)
+		return -1;
+	}
 	else if (c == quotechar)
 	    break;
 	if (has_mbyte)

The patch adds a critical boundary check after incrementing the column index for escape characters. If the new position points to a null terminator (end of line), the function now immediately returns -1 instead of continuing to process potentially invalid memory.

Detection Methods for CVE-2022-1629

Indicators of Compromise

• Unexpected Vim crashes when opening files with unusual escape sequences or quoted text patterns
• Core dumps or crash reports from Vim indicating memory access violations in text object functions
• Files containing malformed quoted strings with trailing backslash sequences designed to trigger the vulnerability

Detection Strategies

• Monitor for abnormal Vim process terminations or segmentation faults during file operations
• Implement file integrity monitoring to detect potentially malicious files with crafted escape sequences
• Deploy endpoint detection rules to identify exploitation attempts targeting text editors
• Use memory sanitizers (ASan, MSan) in development environments to catch buffer over-read attempts

Monitoring Recommendations

• Enable crash reporting and logging for Vim processes to capture exploitation attempts
• Monitor system logs for repeated Vim crashes that may indicate active exploitation
• Track file access patterns to identify suspicious files being opened in Vim
• Implement SentinelOne's behavioral AI to detect anomalous process behavior associated with memory corruption exploits

How to Mitigate CVE-2022-1629

Immediate Actions Required

• Update Vim to version 8.2.4925 or later immediately
• Apply operating system security updates that include patched Vim packages (Fedora, Gentoo, macOS)
• Restrict opening untrusted files in Vim until patches are applied
• Consider using alternative text editors for untrusted content

Patch Information

The vulnerability has been addressed in Vim commit 53a70289c2712808e6d4e88927e03cac01b470dd, which adds proper boundary checking after processing escape characters. Multiple downstream distributions have released security updates:

• Fedora: Security updates available via Fedora Package Announcement
• Gentoo: Patches available per GLSA 202208-32 and GLSA 202305-16
• Apple macOS: Fixed in macOS updates as documented in Apple Support Article HT213488

Workarounds

• Avoid opening files from untrusted sources in Vim until the patch is applied
• Disable or limit text object operations when working with potentially malicious files
• Use Vim's sandbox mode (-S option) when opening untrusted files to restrict functionality
• Consider using containerized or sandboxed environments when editing files of unknown origin

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

# Update Vim on Fedora
sudo dnf update vim

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

# Update Vim on Gentoo
sudo emerge --sync && sudo emerge -u vim