CVE-2021-3501
📋 TL;DR
This vulnerability in the Linux kernel's KVM API allows a user process to trigger an out-of-bounds write by manipulating the internal.ndata value. It affects Linux kernel versions before 5.12, potentially compromising data integrity and system availability. Any system running vulnerable kernel versions with KVM enabled is at risk.
💻 Affected Systems
- Linux kernel
📦 What is this software?
Enterprise Linux For Real Time For Nfv by Redhat
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Enterprise Linux For Real Time For Nfv Tus by Redhat
View all CVEs affecting Enterprise Linux For Real Time For Nfv Tus →
Enterprise Linux For Real Time Tus by Redhat
View all CVEs affecting Enterprise Linux For Real Time Tus →
Fedora by Fedoraproject
Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise leading to data corruption, denial of service, or potential privilege escalation through kernel memory corruption.
Likely Case
System instability, crashes, or denial of service affecting virtualized environments using KVM.
If Mitigated
Limited impact if KVM is not enabled or proper access controls restrict user access to KVM interfaces.
🎯 Exploit Status
Exploitation requires local access and KVM privileges. The vulnerability involves manipulating kernel memory structures.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Linux kernel 5.12 and later
Vendor Advisory: https://bugzilla.redhat.com/show_bug.cgi?id=1950136
Restart Required: Yes
Instructions:
1. Update to Linux kernel 5.12 or later. 2. For Red Hat/CentOS: Apply security updates via 'yum update kernel'. 3. For Ubuntu/Debian: Apply security updates via 'apt update && apt upgrade'. 4. Reboot the system after kernel update.
🔧 Temporary Workarounds
Disable KVM
linuxDisable KVM kernel module if not required for virtualization
modprobe -r kvm
echo 'blacklist kvm' >> /etc/modprobe.d/blacklist.conf
Restrict KVM access
linuxLimit access to KVM device files to trusted users only
chmod 600 /dev/kvm
chown root:root /dev/kvm
🧯 If You Can't Patch
- Disable KVM functionality if not required for system operation
- Implement strict access controls to limit which users can access KVM interfaces
🔍 How to Verify
Check if Vulnerable:
Check kernel version with 'uname -r' and verify if it's below 5.12. Check if KVM is loaded with 'lsmod | grep kvm'.Check Version:
uname -rVerify Fix Applied:
After update, verify kernel version is 5.12 or higher with 'uname -r'. Check that KVM module is still functional if needed.📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs
- System crash dumps
- Unexpected KVM-related errors in dmesg
Network Indicators:
- None - this is a local vulnerability
SIEM Query:
Search for kernel panic events or KVM module errors in system logs🔗 References
- https://bugzilla.redhat.com/show_bug.cgi?id=1950136
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=04c4f2ee3f68c9a4bf1653d15f1a9a435ae33f7a
- https://security.netapp.com/advisory/ntap-20210618-0008/
- https://bugzilla.redhat.com/show_bug.cgi?id=1950136
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=04c4f2ee3f68c9a4bf1653d15f1a9a435ae33f7a
- https://security.netapp.com/advisory/ntap-20210618-0008/
