CVE-2022-36763: Tianocore EDK2 Buffer Overflow Vulnerability

CVE-2022-36763 Overview

CVE-2022-36763 is a heap buffer overflow vulnerability affecting EDK2, the open-source UEFI firmware implementation maintained by TianoCore. The vulnerability exists in the Tcg2MeasureGptTable() function, which is responsible for measuring GPT (GUID Partition Table) data as part of the Trusted Computing Group (TCG) measured boot process. An attacker with local access can exploit this flaw to trigger a heap buffer overflow, potentially compromising the confidentiality, integrity, and availability of the affected system.

Critical Impact

Successful exploitation of this heap buffer overflow vulnerability in UEFI firmware can lead to arbitrary code execution at the firmware level, potentially bypassing Secure Boot protections and establishing persistent system compromise that survives operating system reinstallation.

Affected Products

• Tianocore EDK2 (all versions prior to patch)
• Systems utilizing EDK2-based UEFI firmware implementations
• Fedora and Debian distributions using affected EDK2 packages

Discovery Timeline

• 2024-01-09 - CVE-2022-36763 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2022-36763

Vulnerability Analysis

This vulnerability is classified under CWE-122 (Heap-based Buffer Overflow) and CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The Tcg2MeasureGptTable() function in EDK2 fails to properly validate the size of GPT table entries before copying them into a heap-allocated buffer. When processing specially crafted partition table data, the function can write beyond the allocated heap buffer boundaries, corrupting adjacent memory structures.

The vulnerability occurs during the measured boot process, which is designed to establish a chain of trust by measuring firmware and boot components into the TPM (Trusted Platform Module). Ironically, this security feature contains a flaw that can be exploited to undermine system security.

Root Cause

The root cause of CVE-2022-36763 lies in insufficient bounds checking within the Tcg2MeasureGptTable() function. When processing GPT table entries for TPM measurement, the function allocates a fixed-size heap buffer but does not adequately validate the actual size of the data being copied. This allows an attacker to supply a malformed GPT table that exceeds expected dimensions, resulting in heap memory corruption.

Attack Vector

Exploitation requires local access to the target system. An attacker must be able to manipulate the GPT partition table data that is processed during the boot sequence. This could be achieved through:

• Physical access to modify disk contents
• Privilege escalation to write to raw disk sectors
• Compromising a process with disk write capabilities

Once the malicious GPT data is in place, the vulnerability is triggered during the next system boot when the Tcg2MeasureGptTable() function processes the malformed partition table. The heap overflow can be leveraged to overwrite critical data structures, potentially achieving code execution at the UEFI firmware level.

The local attack vector requires low privileges and no user interaction to exploit, making it a significant risk for systems where attackers have achieved initial access.

Detection Methods for CVE-2022-36763

Indicators of Compromise

• Unexpected modifications to GPT partition table entries with anomalous sizes
• System crashes or unexpected behavior during boot sequence related to TPM measurements
• Firmware integrity check failures or TPM measurement discrepancies
• Evidence of raw disk sector writes by unauthorized processes

Detection Strategies

• Monitor for unauthorized modifications to disk partition tables using file integrity monitoring tools
• Implement TPM-based attestation to detect firmware-level compromises
• Deploy SentinelOne Singularity Platform for real-time detection of suspicious disk access patterns and boot-time anomalies
• Review system logs for boot failures or TPM-related errors that may indicate exploitation attempts

Monitoring Recommendations

• Enable UEFI Secure Boot and verify its configuration remains intact
• Implement hardware-based root of trust mechanisms to detect firmware tampering
• Configure alerts for any processes attempting raw disk writes outside of expected maintenance windows
• Regularly verify TPM PCR (Platform Configuration Register) values against known-good baselines

How to Mitigate CVE-2022-36763

Immediate Actions Required

• Update EDK2 firmware to the latest patched version as specified in the TianoCore Security Advisory
• Apply vendor-specific UEFI firmware updates for affected systems
• Restrict local access and implement strong privilege controls to limit potential attackers' ability to modify disk structures
• Review and update Fedora and Debian systems with patched EDK2 packages as per distribution advisories

Patch Information

TianoCore has released security patches addressing CVE-2022-36763. Organizations should consult the GitHub Security Advisory (GHSA-xvv8-66cq-prwr) for specific patch details. Linux distributions including Fedora and Debian have issued their own package updates, available through their respective security announcement channels.

For Fedora systems, refer to the Fedora Package Announcement for update instructions.

For Debian systems, refer to the Debian LTS Announcement for patching guidance.

Workarounds

• Implement strict access controls to prevent unauthorized users from accessing raw disk devices
• Enable and enforce UEFI Secure Boot to provide an additional layer of protection against firmware-level attacks
• Use full disk encryption with pre-boot authentication to limit opportunities for disk modification
• Consider deploying endpoint detection solutions like SentinelOne that monitor for suspicious boot-time activities and disk access patterns

# Verify current UEFI Secure Boot status
mokutil --sb-state

# Check for available firmware updates on Fedora
sudo dnf update edk2-*

# Check for available firmware updates on Debian
sudo apt update && sudo apt upgrade edk2-*