CVE-2021-4019 – CVE-2021-4019 is a heap-based buffer overflow v... (How to Fix)

Q: What is the severity of CVE-2021-4019?

CVE-2021-4019 has a CVSS score of 7.8 (HIGH). CVE-2021-4019 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 users who open untrusted files with vulnerable Vim versions. The vulnerability requires user interaction but can lead to full system compromise.

📋 TL;DR

CVE-2021-4019 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 users who open untrusted files with vulnerable Vim versions. The vulnerability requires user interaction but can lead to full system compromise.

💻 Affected Systems

Products:

Vim

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 when opening 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, data theft, or lateral movement.

🟠

Likely Case

Local privilege escalation or arbitrary code execution when users open malicious files from untrusted sources.

🟢

If Mitigated

Limited impact if users only open trusted files and have proper privilege separation.

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

🏢 Internal Only: MEDIUM - Internal users could be targeted via phishing or shared malicious 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 publicly available.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Vim 8.2.3999 and later

Vendor Advisory: https://github.com/vim/vim/commit/bd228fd097b41a798f90944b5d1245eddd484142

Restart Required: No

Instructions:

1. Update Vim using your package manager: 'sudo apt update && sudo apt upgrade vim' (Debian/Ubuntu) or 'sudo yum update vim' (RHEL/CentOS). 2. For source installations: download latest Vim from vim.org and compile. 3. Verify version with 'vim --version'.

🔧 Temporary Workarounds

Restrict file opening

all

Configure Vim to not automatically execute commands from files or restrict opening untrusted files.

set secure
set nomodeline

Use alternative editor

all

Temporarily use alternative text editors like nano, emacs, or vscode until patched.

🧯 If You Can't Patch

Implement strict file handling policies: only open files from trusted sources.
Run Vim with reduced privileges using sandboxing tools or as unprivileged user.

🔍 How to Verify

Check if Vulnerable:

Run 'vim --version' and check if version is below 8.2.3999.

Check Version:

vim --version | head -1

Verify Fix Applied:

Run 'vim --version' and confirm version is 8.2.3999 or higher.

📡 Detection & Monitoring

Log Indicators:

Unusual Vim process crashes
Suspicious file access patterns in Vim

Network Indicators:

Unusual outbound connections from Vim processes

SIEM Query:

process_name:vim AND (event_type:crash OR suspicious_parent_process)

📊 Metadata

CVE ID: CVE-2021-4019

CVSS v3 Score: 7.8 (HIGH)

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

CWE: CWE-122

Published: December 1, 2021

Last Updated: November 3, 2025

🔗 References

http://www.openwall.com/lists/oss-security/2022/01/15/1 Mailing List,Third Party Advisory
https://github.com/vim/vim/commit/bd228fd097b41a798f90944b5d1245eddd484142 Patch,Third Party Advisory
https://huntr.dev/bounties/d8798584-a6c9-4619-b18f-001b9a6fca92 Exploit,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/03/msg00018.html Mailing List,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/11/msg00009.html Mailing List,Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DRPAI5JVZLI7WHWSBR6NWAPBQAYUQREW/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FNXY7T5OORA7UJIMGSJBGHFMU6UZWS6P/
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/bd228fd097b41a798f90944b5d1245eddd484142 Patch,Third Party Advisory
https://huntr.dev/bounties/d8798584-a6c9-4619-b18f-001b9a6fca92 Exploit,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/03/msg00018.html Mailing List,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/11/msg00009.html Mailing List,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2025/03/msg00023.html
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DRPAI5JVZLI7WHWSBR6NWAPBQAYUQREW/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FNXY7T5OORA7UJIMGSJBGHFMU6UZWS6P/
https://security.gentoo.org/glsa/202208-32 Third Party Advisory

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