CVE-2020-25632
📋 TL;DR
This CVE-2020-25632 vulnerability in GRUB2 allows attackers to unload kernel modules that other modules depend on, creating a use-after-free condition that can lead to arbitrary code execution. It affects systems using GRUB2 versions prior to 2.06, potentially bypassing Secure Boot protections. The flaw threatens data confidentiality, integrity, and system availability.
💻 Affected Systems
- GRUB2
- Linux distributions using GRUB2 bootloader
📦 What is this software?
Fedora by Fedoraproject
Fedora by Fedoraproject
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with Secure Boot bypass, allowing persistent malware installation and full control over the boot process.
Likely Case
Local privilege escalation to kernel-level access, enabling data theft, system manipulation, or denial of service.
If Mitigated
Limited impact if Secure Boot is properly configured with trusted keys and modules are restricted, though risk remains for local attackers.
🎯 Exploit Status
Exploitation requires local access and knowledge of module dependencies. Proof-of-concept code exists in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: GRUB2 2.06 or later
Vendor Advisory: https://bugzilla.redhat.com/show_bug.cgi?id=1879577
Restart Required: Yes
Instructions:
1. Update GRUB2 package to version 2.06 or later using your distribution's package manager. 2. For Red Hat/Fedora: 'sudo dnf update grub2'. 3. For Debian/Ubuntu: 'sudo apt update && sudo apt upgrade grub2'. 4. Regenerate GRUB configuration: 'sudo grub2-mkconfig -o /boot/grub2/grub.cfg'. 5. Reboot the system.
🔧 Temporary Workarounds
Restrict physical and local access
allLimit who has physical or local console access to vulnerable systems
Enable Secure Boot with trusted keys only
linuxConfigure UEFI Secure Boot to only allow signed modules from trusted sources
sudo mokutil --enable-validation
sudo mokutil --import-key /path/to/key.der
🧯 If You Can't Patch
- Implement strict access controls to prevent unauthorized local access to systems
- Monitor for unusual GRUB module loading/unloading activity in system logs
🔍 How to Verify
Check if Vulnerable:
Check GRUB2 version: 'grub2-install --version' or 'dpkg -l | grep grub' or 'rpm -q grub2'Check Version:
grub2-install --versionVerify Fix Applied:
Verify GRUB2 version is 2.06 or higher: 'grub2-install --version | grep -q "2.0[6-9]\|2.[1-9]" && echo "Patched"'📡 Detection & Monitoring
Log Indicators:
- Unusual GRUB module operations in boot logs
- Failed Secure Boot validations
- Unexpected kernel module loading/unloading
Network Indicators:
- None - local exploit only
SIEM Query:
source="boot.log" AND ("grub" OR "module") AND ("unload" OR "rmmod")🔗 References
- https://bugzilla.redhat.com/show_bug.cgi?id=1879577
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZWZ36QK4IKU6MWDWNOOWKPH3WXZBHT2R/
- https://security.gentoo.org/glsa/202104-05
- https://security.netapp.com/advisory/ntap-20220325-0001/
- https://bugzilla.redhat.com/show_bug.cgi?id=1879577
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZWZ36QK4IKU6MWDWNOOWKPH3WXZBHT2R/
- https://security.gentoo.org/glsa/202104-05
- https://security.netapp.com/advisory/ntap-20220325-0001/
