CVE-2021-39256
📋 TL;DR
This vulnerability allows an attacker to trigger a heap-based buffer overflow by providing a malicious NTFS image to NTFS-3G. Systems using NTFS-3G versions before 2021.8.22 to mount NTFS filesystems are affected, potentially allowing arbitrary code execution.
💻 Affected Systems
- NTFS-3G
📦 What is this software?
Ntfs 3g by Tuxera
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with root privileges if NTFS-3G is running as root during mount operations, leading to complete system compromise.
Likely Case
Local privilege escalation or denial of service when mounting a crafted NTFS image, potentially allowing attackers to gain elevated privileges.
If Mitigated
Limited impact if NTFS-3G runs with reduced privileges or if untrusted NTFS images are not mounted.
🎯 Exploit Status
Exploitation requires the attacker to provide a malicious NTFS image that gets mounted. Proof-of-concept code exists in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2021.8.22 and later
Vendor Advisory: https://github.com/tuxera/ntfs-3g/security/advisories/GHSA-q759-8j5v-q5jp
Restart Required: No
Instructions:
1. Update NTFS-3G to version 2021.8.22 or later using your distribution's package manager. 2. For Debian/Ubuntu: sudo apt update && sudo apt install ntfs-3g. 3. For RHEL/CentOS: sudo yum update ntfs-3g. 4. For Gentoo: emerge --sync && emerge -av ntfs-3g.
🔧 Temporary Workarounds
Mount NTFS with noexec option
linuxPrevents execution of binaries from mounted NTFS filesystems, reducing attack surface.
mount -t ntfs-3g -o noexec /dev/sdX1 /mnt/ntfs
Run NTFS-3G with reduced privileges
linuxConfigure NTFS-3G to run as non-root user where possible.
chmod u-s /usr/bin/ntfs-3g
adduser --system --group ntfsuser
mount -t ntfs-3g -o uid=ntfsuser /dev/sdX1 /mnt/ntfs
🧯 If You Can't Patch
- Avoid mounting NTFS filesystems from untrusted sources
- Implement strict access controls on mount points and monitor for unusual mount activity
🔍 How to Verify
Check if Vulnerable:
Check NTFS-3G version: ntfs-3g --version | head -1Check Version:
ntfs-3g --version | head -1Verify Fix Applied:
Verify version is 2021.8.22 or higher: ntfs-3g --version | grep -q '2021.8.22\|2021.8.23\|2021.8.24\|2021.9\|2022' && echo 'Patched' || echo 'Vulnerable'📡 Detection & Monitoring
Log Indicators:
- Kernel logs showing NTFS mount failures or crashes
- System logs with ntfs-3g process termination
Network Indicators:
- Unusual network shares being mounted
- SMB/NTFS traffic from unexpected sources
SIEM Query:
process_name:"ntfs-3g" AND (event_type:"crash" OR exit_code:139)🔗 References
- https://github.com/tuxera/ntfs-3g/releases
- https://github.com/tuxera/ntfs-3g/security/advisories/GHSA-q759-8j5v-q5jp
- https://lists.debian.org/debian-lts-announce/2021/11/msg00013.html
- https://security.gentoo.org/glsa/202301-01
- https://www.debian.org/security/2021/dsa-4971
- https://github.com/tuxera/ntfs-3g/releases
- https://github.com/tuxera/ntfs-3g/security/advisories/GHSA-q759-8j5v-q5jp
- https://lists.debian.org/debian-lts-announce/2021/11/msg00013.html
- https://security.gentoo.org/glsa/202301-01
- https://www.debian.org/security/2021/dsa-4971
