CVE-2025-22134: Vim Buffer Overflow Vulnerability

CVE-2025-22134 Overview

CVE-2025-22134 is a heap-buffer-overflow vulnerability in Vim that occurs when switching to other buffers using the :all command while visual mode is still active. The vulnerability arises because Vim does not properly end visual mode before opening other windows and buffers, which may cause the application to access memory beyond the end of a line in a buffer.

Critical Impact

This heap-buffer-overflow can lead to denial of service through application crashes when users execute the :all ex command while visual mode is active.

Affected Products

• Vim versions prior to patch 9.1.1003
• NetApp Bootstrap OS
• NetApp HCI Compute Node

Discovery Timeline

• 2025-01-11 - Vulnerability disclosed on OpenWall OSS-Security mailing list
• 2025-01-13 - CVE CVE-2025-22134 published to NVD
• 2025-08-14 - Last updated in NVD database

Technical Details for CVE-2025-22134

Vulnerability Analysis

This vulnerability is classified as CWE-122 (Heap-based Buffer Overflow). The issue stems from improper state management in Vim when processing the :all command. When a user enters visual mode and then executes the :all command to open all argument files in separate windows, Vim fails to properly reset visual mode before switching buffers. This leads to an out-of-bounds memory access when the editor attempts to reference cursor positions that are valid in the original buffer but exceed the line length in the new buffer.

The vulnerability requires local access and user interaction, as the user must have visual mode active when executing the :all ex command. While exploitation could result in application crashes and denial of service, the impact is contained to availability without affecting confidentiality or integrity.

Root Cause

The root cause is insufficient state management in Vim's buffer switching logic. When the :all command is executed, Vim opens multiple windows for argument files but fails to call reset_VIsual_and_resel() to properly terminate visual mode. This leaves the cursor position and VIsual marker potentially referencing invalid positions in the newly opened buffers, as these positions may exceed the actual line lengths in the target buffers.

Additionally, the gchar_pos() function in src/misc1.c lacked proper bounds checking to verify that the requested column position does not exceed the buffer line length before attempting to access character data.

Attack Vector

The attack vector is local and requires user interaction. An attacker would need to craft a malicious set of files or convince a user to perform the following sequence:

1. Open Vim with multiple file arguments
2. Enter visual mode (e.g., by pressing v, V, or Ctrl-V)
3. Execute the :all command while visual mode is active

This specific sequence triggers the heap-buffer-overflow condition when Vim attempts to access character positions that are valid in the original buffer but exceed the bounds of lines in subsequently opened buffers.

// Security patch in src/arglist.c
// Source: https://github.com/vim/vim/commit/c9a1e257f1630a0866447e53a564f7ff96a80ead
 
    tabpage_T *new_lu_tp = curtab;
 
+    // Stop Visual mode, the cursor and "VIsual" may very well be invalid after
+    // switching to another buffer.
+    reset_VIsual_and_resel();
+
    // Try closing all windows that are not in the argument list.
    // Also close windows that are not full width;
    // When 'hidden' or "forceit" set the buffer becomes hidden.

// Security patch in src/misc1.c - bounds checking addition
// Source: https://github.com/vim/vim/commit/c9a1e257f1630a0866447e53a564f7ff96a80ead
gchar_pos(pos_T *pos)
{
    char_u	*ptr;
+    int		ptrlen;
 
    // When searching columns is sometimes put at the end of a line.
    if (pos->col == MAXCOL)
	return NUL;
+    ptrlen = ml_get_len(pos->lnum);
    ptr = ml_get_pos(pos);
+    if (pos->col > ptrlen)
+	return NUL;
    if (has_mbyte)
	return (*mb_ptr2char)(ptr);
    return (int)*ptr;

Detection Methods for CVE-2025-22134

Indicators of Compromise

• Unexpected Vim crashes or segmentation faults when working with multiple files
• Core dumps generated by Vim processes indicating heap corruption
• Application error logs showing memory access violations during buffer operations
• Unusual Vim process terminations when using the :all command

Detection Strategies

• Monitor system logs for Vim segmentation faults and crash reports
• Implement application crash monitoring to detect patterns of Vim failures
• Use memory sanitizers (ASan, MSan) in development environments to catch heap overflows
• Deploy endpoint detection tools to identify abnormal Vim process behavior

Monitoring Recommendations

• Enable crash reporting and core dump collection for Vim processes
• Monitor for repeated Vim process restarts that may indicate exploitation attempts
• Implement host-based intrusion detection to flag unusual memory access patterns
• Review system audit logs for suspicious Vim command patterns

How to Mitigate CVE-2025-22134

Immediate Actions Required

• Update Vim to version 9.1.1003 or later immediately
• Apply vendor patches from the official Vim repository
• Review NetApp advisory ntap-20250314-0004 if using affected NetApp products
• Consider using alternative text editors temporarily if immediate patching is not possible

Patch Information

The vulnerability has been fixed in Vim patch v9.1.1003. The fix includes two key changes:

1. State Reset: Adding a call to reset_VIsual_and_resel() in src/arglist.c before opening other windows and buffers when executing the :all command
2. Bounds Checking: Adding validation in gchar_pos() in src/misc1.c to verify that the column position does not exceed the buffer line length before accessing character data

Users should update through their package manager or compile from source with the latest patches. The Vim project credited GitHub user gandalf4a for reporting this issue.

For additional details, see the GitHub Security Advisory GHSA-5rgf-26wj-48v8.

Workarounds

• Avoid using the :all command while in visual mode until patching is complete
• Exit visual mode (press Escape) before executing any buffer-switching commands
• Use alternative buffer management commands like :args followed by individual :edit commands
• Implement process sandboxing to limit the impact of potential crashes

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

# Update Vim on RHEL/CentOS systems
sudo yum update vim-enhanced

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