CVE-2021-4136
📋 TL;DR
CVE-2021-4136 is a heap-based buffer overflow vulnerability in Vim that allows attackers to execute arbitrary code by tricking users into opening specially crafted files. This affects all users who open malicious files with vulnerable Vim versions. The vulnerability stems from improper bounds checking when processing certain file formats.
💻 Affected Systems
- Vim
- Neovim (if using vulnerable Vim components)
- Applications embedding Vim
📦 What is this software?
Fedora by Fedoraproject
Fedora by Fedoraproject
Macos by Apple
macOS is Apple's desktop and laptop operating system powering Mac computers used by millions of professionals, developers, creative professionals, and enterprise users worldwide. Built on a Unix foundation with the Darwin kernel and modern Cocoa frameworks, macOS delivers a seamless ecosystem integr...
Learn more about Macos →Macos by Apple
macOS is Apple's desktop and laptop operating system powering Mac computers used by millions of professionals, developers, creative professionals, and enterprise users worldwide. Built on a Unix foundation with the Darwin kernel and modern Cocoa frameworks, macOS delivers a seamless ecosystem integr...
Learn more about Macos →Vim by Vim
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the user running Vim, potentially leading to full system compromise if the user has elevated privileges.
Likely Case
Local privilege escalation or arbitrary code execution when a user opens a malicious file, potentially leading to data theft or further lateral movement.
If Mitigated
Limited impact if Vim is run with reduced privileges or in sandboxed environments, though data exposure may still occur.
🎯 Exploit Status
Exploitation requires user interaction (opening a malicious file). Proof-of-concept code has been published in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Vim 8.2.4434 and later
Vendor Advisory: https://github.com/vim/vim/commit/605ec91e5a7330d61be313637e495fa02a6dc264
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 version from vim.org. 4. For macOS: 'brew upgrade vim' or download from official site.
🔧 Temporary Workarounds
Disable vulnerable file type processing
allConfigure Vim to avoid processing the specific file types that trigger the vulnerability
Add 'set nomodeline' to ~/.vimrc to disable modeline processing
Add 'set secure' to ~/.vimrc for enhanced security
Run Vim with reduced privileges
linuxExecute Vim with minimal privileges to limit potential damage from exploitation
sudo -u nobody vim file.txt
runuser -l lowprivuser -c 'vim file.txt'
🧯 If You Can't Patch
- Restrict Vim usage to trusted files only and avoid opening unknown or untrusted documents
- Implement application whitelisting to prevent execution of vulnerable Vim versions
🔍 How to Verify
Check if Vulnerable:
Check Vim version with 'vim --version' and verify it's older than 8.2.4434Check Version:
vim --version | head -1Verify Fix Applied:
Run 'vim --version' and confirm version is 8.2.4434 or newer, or check for commit 605ec91e5a7330d61be313637e495fa02a6dc264 in build info📡 Detection & Monitoring
Log Indicators:
- Unusual Vim process crashes
- Suspicious file access patterns in Vim
- Unexpected child processes spawned from Vim
Network Indicators:
- Outbound connections from Vim process to unexpected destinations
- File downloads triggered by Vim sessions
SIEM Query:
process_name:vim AND (event_id:1000 OR event_id:1001) OR parent_process:vim AND process_creation🔗 References
- http://seclists.org/fulldisclosure/2022/Jul/14
- http://seclists.org/fulldisclosure/2022/Mar/29
- http://seclists.org/fulldisclosure/2022/May/35
- http://www.openwall.com/lists/oss-security/2022/01/15/1
- https://github.com/vim/vim/commit/605ec91e5a7330d61be313637e495fa02a6dc264
- https://huntr.dev/bounties/5c6b93c1-2d27-4e98-a931-147877b8c938
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2EY2VFBU3YGGWI5BW4XKT3F37MYGEQUD/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3FH2J57GDA2WMBS6J56F6QQRA6BXQQFZ/
- https://security.gentoo.org/glsa/202208-32
- https://support.apple.com/kb/HT213183
- https://support.apple.com/kb/HT213256
- https://support.apple.com/kb/HT213343
- http://seclists.org/fulldisclosure/2022/Jul/14
- http://seclists.org/fulldisclosure/2022/Mar/29
- http://seclists.org/fulldisclosure/2022/May/35
- http://www.openwall.com/lists/oss-security/2022/01/15/1
- https://github.com/vim/vim/commit/605ec91e5a7330d61be313637e495fa02a6dc264
- https://huntr.dev/bounties/5c6b93c1-2d27-4e98-a931-147877b8c938
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2EY2VFBU3YGGWI5BW4XKT3F37MYGEQUD/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3FH2J57GDA2WMBS6J56F6QQRA6BXQQFZ/
- https://security.gentoo.org/glsa/202208-32
- https://support.apple.com/kb/HT213183
- https://support.apple.com/kb/HT213256
- https://support.apple.com/kb/HT213343
