CVE-2021-3968 – CVE-2021-3968 is a heap-based buffer overflow v... (How to Fix)

Q: What is the severity of CVE-2021-3968?

CVE-2021-3968 has a CVSS score of 8.0 (HIGH). CVE-2021-3968 is a heap-based buffer overflow vulnerability in Vim text editor that allows attackers to execute arbitrary code by tricking users into opening specially crafted files. This affects all users who open untrusted files with vulnerable Vim versions. The vulnerability occurs due to improper bounds checking when processing certain file formats.

📋 TL;DR

CVE-2021-3968 is a heap-based buffer overflow vulnerability in Vim text editor that allows attackers to execute arbitrary code by tricking users into opening specially crafted files. This affects all users who open untrusted files with vulnerable Vim versions. The vulnerability occurs due to improper bounds checking when processing certain file formats.

💻 Affected Systems

Products:

Vim
Neovim (potentially affected)
gVim
vim-enhanced packages

Versions: Vim versions before 8.2.3999

Operating Systems: Linux, Unix-like systems, Windows, macOS

Default Config Vulnerable: ⚠️ Yes

Notes: All default installations of affected Vim versions are vulnerable. The vulnerability is triggered when opening specially crafted files.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with the privileges of the Vim user, potentially leading to full system compromise if Vim is run with elevated privileges.

🟠

Likely Case

Local privilege escalation or arbitrary code execution when users open malicious files, potentially leading to data theft or lateral movement.

🟢

If Mitigated

Limited impact if Vim runs with restricted privileges and users avoid opening untrusted files.

🌐 Internet-Facing: LOW - Vim is typically not directly internet-facing, though could be exploited via web interfaces that allow file uploads.

🏢 Internal Only: MEDIUM - High risk for developers and system administrators who frequently use Vim to edit various files.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires user interaction to open a malicious file. Proof-of-concept code is available in public repositories.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Vim 8.2.3999 and later

Vendor Advisory: https://github.com/vim/vim/commit/a062006b9de0b2947ab5fb376c6e67ef92a8cd69

Restart Required: No

Instructions:

1. Update Vim using your system's package manager. 2. For Linux: 'sudo apt update && sudo apt upgrade vim' (Debian/Ubuntu) or 'sudo yum update vim' (RHEL/CentOS). 3. For Windows: Download latest installer from vim.org. 4. For macOS: 'brew upgrade vim' or download from vim.org.

🔧 Temporary Workarounds

Restrict file types

all

Configure Vim to avoid processing potentially dangerous file formats

Add 'set nomodeline' to ~/.vimrc to disable modeline processing

Use sandboxed environment

linux

Run Vim in a container or sandbox when opening untrusted files

firejail vim untrusted_file.txt
bwrap --dev-bind / / -- vim untrusted_file.txt

🧯 If You Can't Patch

Restrict Vim usage to trusted users only and implement strict file handling policies
Use alternative text editors for opening untrusted files and implement application whitelisting

🔍 How to Verify

Check if Vulnerable:

Check Vim version: 'vim --version | head -1'. If version is below 8.2.3999, system is vulnerable.

Check Version:

vim --version | head -1

Verify Fix Applied:

After update, verify version is 8.2.3999 or higher: 'vim --version | head -1'

📡 Detection & Monitoring

Log Indicators:

Segmentation fault or crash logs from Vim processes
Unexpected child process creation from Vim

Network Indicators:

Unusual outbound connections from systems where Vim was recently used

SIEM Query:

process_name:vim AND (event_type:crash OR parent_process:unusual)

📊 Metadata

CVE ID: CVE-2021-3968

CVSS v3 Score: 8.0 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H

CWE: CWE-122

Published: November 19, 2021

Last Updated: November 21, 2024

🔗 References

http://www.openwall.com/lists/oss-security/2022/01/15/1 Mailing List,Third Party Advisory
https://github.com/vim/vim/commit/a062006b9de0b2947ab5fb376c6e67ef92a8cd69 Patch,Third Party Advisory
https://huntr.dev/bounties/00d62924-a7b4-4a61-ba29-acab2eaa1528 Exploit,Issue Tracking,Patch,Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FNXY7T5OORA7UJIMGSJBGHFMU6UZWS6P/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IH2LS2DXBTYOCWGAKFMBF3HTWWXPBEFL/
https://security.gentoo.org/glsa/202208-32 Third Party Advisory
http://www.openwall.com/lists/oss-security/2022/01/15/1 Mailing List,Third Party Advisory
https://github.com/vim/vim/commit/a062006b9de0b2947ab5fb376c6e67ef92a8cd69 Patch,Third Party Advisory
https://huntr.dev/bounties/00d62924-a7b4-4a61-ba29-acab2eaa1528 Exploit,Issue Tracking,Patch,Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FNXY7T5OORA7UJIMGSJBGHFMU6UZWS6P/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IH2LS2DXBTYOCWGAKFMBF3HTWWXPBEFL/
https://security.gentoo.org/glsa/202208-32 Third Party Advisory

📤 Share & Export

📄 Export Markdown 📋 Export JSON

🔗 Related Vulnerabilities

If you're affected by CVE-2021-3968, you might also want to check these: