CVE-2021-31872
📋 TL;DR
This vulnerability in klibc's cpio command allows integer overflows on 32-bit systems that can lead to buffer overflows. Attackers could potentially execute arbitrary code or cause denial of service. Systems using klibc versions before 2.0.9 on 32-bit architectures are affected.
💻 Affected Systems
- klibc
- systems using klibc utilities
- initramfs tools
📦 What is this software?
Klibc by Klibc Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with root privileges leading to complete system compromise
Likely Case
Local privilege escalation or denial of service through cpio command manipulation
If Mitigated
Limited impact if proper input validation and sandboxing are in place
🎯 Exploit Status
Exploitation requires ability to trigger cpio operations with malicious input; proof-of-concept details are publicly available
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.0.9 and later
Vendor Advisory: https://lists.zytor.com/archives/klibc/2021-April/004593.html
Restart Required: No
Instructions:
1. Update klibc package to version 2.0.9 or later
2. Update any dependent packages (like initramfs tools)
3. Rebuild initramfs if using klibc in initramfs
4. Verify the update with version check
🔧 Temporary Workarounds
Disable vulnerable cpio usage
linuxRemove or restrict cpio command usage in scripts and automated processes
chmod -x /usr/bin/cpio
mv /usr/bin/cpio /usr/bin/cpio.disabled
Use 64-bit systems
linuxMigrate to 64-bit systems where integer overflow risk is reduced
🧯 If You Can't Patch
- Implement strict input validation for cpio operations
- Run cpio commands with minimal privileges using sudo restrictions or containers
🔍 How to Verify
Check if Vulnerable:
Check klibc version: dpkg -l | grep klibc or rpm -qa | grep klibcCheck Version:
dpkg -l | grep klibc || rpm -qa | grep klibc || find /lib -name '*klibc*' -exec strings {} \; | grep -i versionVerify Fix Applied:
Verify version is 2.0.9 or higher: klibc-version or check package version📡 Detection & Monitoring
Log Indicators:
- Unusual cpio command usage
- Process crashes related to cpio
- Suspicious initramfs operations
Network Indicators:
- N/A (local vulnerability)
SIEM Query:
process_name="cpio" AND (process_args CONTAINS "-I" OR process_args CONTAINS "-O")🔗 References
- http://www.openwall.com/lists/oss-security/2021/04/30/1
- https://git.kernel.org/pub/scm/libs/klibc/klibc.git/commit/?id=9b1c91577aef7f2e72c3aa11a27749160bd278ff
- https://kernel.org/pub/linux/libs/klibc/2.0/
- https://lists.debian.org/debian-lts-announce/2021/06/msg00025.html
- https://lists.zytor.com/archives/klibc/2021-April/004593.html
- http://www.openwall.com/lists/oss-security/2021/04/30/1
- https://git.kernel.org/pub/scm/libs/klibc/klibc.git/commit/?id=9b1c91577aef7f2e72c3aa11a27749160bd278ff
- https://kernel.org/pub/linux/libs/klibc/2.0/
- https://lists.debian.org/debian-lts-announce/2021/06/msg00025.html
- https://lists.zytor.com/archives/klibc/2021-April/004593.html
