CVE-2021-31870
📋 TL;DR
CVE-2021-31870 is an integer overflow vulnerability in klibc's calloc() function that can lead to heap buffer overflow. This allows attackers to potentially execute arbitrary code or crash affected systems. Systems using klibc versions before 2.0.9 are vulnerable.
💻 Affected Systems
- klibc
📦 What is this software?
Klibc by Klibc Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, privilege escalation, or denial of service.
Likely Case
Application crashes or denial of service affecting system stability.
If Mitigated
Limited impact if proper memory protections (ASLR, stack canaries) are enabled and the vulnerability is not reachable.
🎯 Exploit Status
Exploitation requires control over calloc() parameters to trigger integer overflow; no public exploits have been documented.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.0.9
Vendor Advisory: https://lists.zytor.com/archives/klibc/2021-April/004593.html
Restart Required: Yes
Instructions:
1. Update klibc to version 2.0.9 or later. 2. Rebuild any initramfs images that include klibc. 3. Reboot the system to ensure updated libraries are loaded.
🔧 Temporary Workarounds
Disable vulnerable utilities
linuxIdentify and disable applications that use the vulnerable klibc calloc() function.
Identify using: ldd /path/to/binary | grep klibc
Disable or remove affected binaries
🧯 If You Can't Patch
- Implement strict access controls to limit who can execute klibc-dependent applications.
- Enable security mitigations like ASLR and stack canaries to reduce exploit success probability.
🔍 How to Verify
Check if Vulnerable:
Check klibc version: dpkg -l | grep klibc or rpm -qa | grep klibcCheck Version:
klibc-version 2>/dev/null || echo "Check via package manager"Verify Fix Applied:
Verify klibc version is 2.0.9 or higher using package manager commands.📡 Detection & Monitoring
Log Indicators:
- Application crashes with segmentation faults in klibc-dependent programs
- Unexpected memory allocation patterns
Network Indicators:
- None specific to this vulnerability
SIEM Query:
Search for process crashes involving klibc libraries or initramfs utilities.🔗 References
- http://www.openwall.com/lists/oss-security/2021/04/30/1
- https://git.kernel.org/pub/scm/libs/klibc/klibc.git/commit/?id=292650f04c2b5348b4efbad61fb014ed09b4f3f2
- 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=292650f04c2b5348b4efbad61fb014ed09b4f3f2
- 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
