CVE-2020-10713: GNU GRUB2 RCE Vulnerability

CVE-2020-10713 Overview

A critical buffer overflow vulnerability, commonly known as "BootHole," was discovered in GRUB2 bootloader versions prior to 2.06. This flaw enables attackers to hijack and tamper with the GRUB verification process, effectively bypassing Secure Boot protections on affected systems. The vulnerability allows an attacker with local access to craft malicious strings in the GRUB2 configuration file (grub.cfg) that cause a buffer overflow, leading to arbitrary code execution within the GRUB environment before the operating system loads.

Critical Impact

This vulnerability allows attackers to bypass Secure Boot protections and execute arbitrary code during the boot process, compromising system integrity before the operating system even loads. This enables persistent, stealthy malware that survives OS reinstallation.

Affected Products

• GNU GRUB2 (versions prior to 2.06)
• Debian Linux 10.0
• openSUSE Leap 15.1 and 15.2
• VMware Photon OS

Discovery Timeline

• July 30, 2020 - CVE-2020-10713 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-10713

Vulnerability Analysis

The BootHole vulnerability exists in how GRUB2 parses its configuration file (grub.cfg). When processing configuration directives, GRUB2 fails to properly validate the length of certain input strings before copying them into fixed-size memory buffers. This classic buffer overflow condition (CWE-120) allows attackers to overwrite adjacent memory regions with attacker-controlled data.

The vulnerability is particularly dangerous because GRUB2 executes in a highly privileged context—before the operating system loads and before most security controls are active. Code execution at this stage operates outside the visibility of endpoint security solutions and can persist across OS reinstallations since the bootloader resides on a separate partition.

To exploit this vulnerability, an attacker requires one of the following access conditions: physical access to the target system, the ability to modify PXE boot network configurations, or remote root access to a networked system. With such access, the attacker can modify the grub.cfg file to include malicious strings that trigger the buffer overflow during boot.

Root Cause

The root cause is improper bounds checking when GRUB2 parses configuration file entries. The grub.cfg file parser does not validate input lengths before copying configuration data into fixed-size buffers on the stack or heap. When an attacker supplies specially crafted, oversized input values in the configuration file, the parser writes beyond the allocated buffer boundaries, corrupting adjacent memory structures and enabling control flow hijacking.

Attack Vector

The attack requires local access to the system—either through physical presence, compromised administrator credentials, or control over network boot infrastructure. An attacker with the ability to write to the EFI System Partition (ESP) or GRUB configuration files can craft malicious configuration entries containing oversized strings. During the next boot cycle, GRUB2 parses the malicious configuration, triggers the buffer overflow, and executes attacker-supplied shellcode. Because this occurs before Secure Boot verification completes, the malicious code runs with full hardware privileges and can install persistent bootkits or rootkits.

The vulnerability mechanism involves crafting oversized configuration values that exceed the expected buffer size. When GRUB2's configuration parser processes these values, it copies the data without proper length validation, overwriting return addresses or function pointers that enable arbitrary code execution. For detailed technical analysis, see the Eclypsium Security Analysis.

Detection Methods for CVE-2020-10713

Indicators of Compromise

• Unexpected modifications to grub.cfg or other GRUB2 configuration files on the EFI System Partition
• Changes to the EFI System Partition outside of normal system update processes
• Anomalous boot behavior or extended boot times indicating malicious code execution
• Unsigned or tampered GRUB2 binaries present on the system

Detection Strategies

• Monitor file integrity of the EFI System Partition and GRUB configuration files using cryptographic hashes
• Implement boot measurement and attestation using TPM (Trusted Platform Module) to detect unauthorized boot chain modifications
• Review system logs for unexpected mount operations on the EFI System Partition
• Use firmware security scanning tools to verify bootloader integrity against known-good states

Monitoring Recommendations

• Enable Secure Boot logging and audit events related to boot component verification failures
• Implement continuous monitoring of EFI System Partition access patterns and file modifications
• Deploy endpoint detection capabilities that can inspect pre-boot components during runtime
• Configure alerts for any administrative access to bootloader configuration files

How to Mitigate CVE-2020-10713

Immediate Actions Required

• Update GRUB2 to version 2.06 or later, which includes the security fix for this vulnerability
• Apply vendor-specific security updates for your Linux distribution immediately
• Revoke vulnerable GRUB2 binaries by updating the Secure Boot DBX (forbidden signature database)
• Restrict write access to the EFI System Partition to prevent unauthorized configuration modifications

Patch Information

Security patches have been released by major Linux distributions and vendors. Organizations should apply the appropriate updates for their environment:

• Debian Security Advisory DSA-4735
• Ubuntu Security Notice USN-4432-1
• openSUSE Security Announcements
• VMware Knowledge Base Article 80181
• Cisco Security Advisory
• NetApp Security Advisory
• Gentoo GLSA 202104-05

Additional coordination information is available in the CERT Vulnerability Note VU#174059.

Workarounds

• Implement strict physical security controls to prevent unauthorized access to boot partitions
• Use full disk encryption with pre-boot authentication to protect against offline configuration tampering
• Enable UEFI password protection to prevent unauthorized boot configuration changes
• Consider disabling PXE boot if network boot functionality is not required

# Verify GRUB2 version on Debian/Ubuntu systems
grub-install --version

# Check for available security updates
apt update && apt list --upgradable | grep grub

# Update GRUB2 packages
apt install grub-efi-amd64-signed grub2-common

# Regenerate GRUB configuration after update
update-grub