^{CVE-2020-10713:}GRUB2 buffer overflow vulnerability (CVE-2020-10713) allows attackers to bypass Secure Boot protections and execute arbitrary code during boot.

Overview

CVE-2020-10713, also known as "BootHole," is a severe security vulnerability affecting GRUB2 bootloaders prior to version 2.06. The vulnerability stems from a buffer overflow condition that can be exploited to execute arbitrary code during the boot process. What makes this vulnerability particularly dangerous is its ability to bypass Secure Boot, a security feature designed to ensure only trusted software runs during system startup.

The vulnerability exists in the way GRUB2 parses grub.cfg configuration files. Since this file isn't covered by Secure Boot protections, attackers can modify it to include specially crafted strings that trigger buffer overflows, leading to code execution in the GRUB2 context. This effectively undermines the entire secure boot process, as it allows attackers to load modified or malicious operating system kernels despite Secure Boot being enabled.

Exploitation requires some form of initial access to the target system, such as physical access, control over PXE boot infrastructure, or existing remote root access to the system. Once exploited, attackers gain persistent access that's difficult to detect and can survive operating system reinstallation.

Remediation

To mitigate the vulnerability, system administrators should take the following actions:

1. Update GRUB2 to version 2.06 or later, which contains patches for this vulnerability.

2. Apply vendor-specific security updates:

   • For Red Hat systems: Follow the guidance in Red Hat Bugzilla #1825243
   • For Debian systems: Apply DSA-4735 security updates
   • For Ubuntu systems: Apply USN-4432-1 security updates
   • For openSUSE: Apply openSUSE-SU-2020:1168 or openSUSE-SU-2020:1169 as appropriate
   • For other distributions: Apply vendor-provided security updates

3. Update firmware/UEFI:

   • Check with hardware vendors for firmware updates that address this vulnerability
   • Apply UEFI revocation updates to block vulnerable bootloaders

4. Implement additional security measures:

   • Restrict physical access to critical systems
   • Secure PXE boot environments with proper authentication
   • Monitor boot-related files for unauthorized changes
   • Consider implementing multi-factor authentication for BIOS/UEFI configuration changes

5. Verify Secure Boot is properly configured and enabled after applying updates.

References

1. Technical analysis: https://eclypsium.com/2020/07/29/theres-a-hole-in-the-boot/
2. Red Hat Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1825243
3. US-CERT Vulnerability Note: https://www.kb.cert.org/vuls/id/174059
4. Debian Security Advisory: https://www.debian.org/security/2020/dsa-4735
5. Ubuntu Security Notice: https://usn.ubuntu.com/4432-1/
6. openSUSE Security Updates:
   • http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00016.html
   • http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00017.html
7. Cisco Security Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-grub2-code-exec-xLePCAPY
8. NetApp Security Advisory: https://security.netapp.com/advisory/ntap-20200731-0008/
9. VMware Knowledge Base Article: https://kb.vmware.com/s/article/80181
10. OSS-Security Mailing List Discussion: http://www.openwall.com/lists/oss-security/2020/07/29/3