CVE-2023-45234: Tianocore EDK2 Buffer Overflow Vulnerability

CVE-2023-45234 Overview

EDK2's Network Package is susceptible to a buffer overflow vulnerability when processing DNS Servers option from a DHCPv6 Advertise message. This vulnerability can be exploited by an attacker to gain unauthorized access and potentially lead to a loss of Confidentiality, Integrity and/or Availability. The vulnerability is part of a collection of UEFI firmware flaws collectively known as "PixieFail" that affect the network boot process.

Critical Impact

An adjacent network attacker can exploit this buffer overflow in EDK2's DHCPv6 implementation to achieve remote code execution during the PXE boot process, potentially compromising systems before the operating system loads.

Affected Products

• Tianocore EDK2 (all versions prior to patch)
• Systems using EDK2-based UEFI firmware with PXE boot enabled
• Enterprise and data center systems utilizing network boot functionality

Discovery Timeline

• 2024-01-16 - CVE-2023-45234 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2023-45234

Vulnerability Analysis

This buffer overflow vulnerability exists within EDK2's Network Package, specifically in the code responsible for processing DHCPv6 Advertise messages. When the firmware parses the DNS Servers option within a DHCPv6 response, insufficient bounds checking allows an attacker to overflow a buffer by providing a maliciously crafted DNS Servers option.

The vulnerability requires the attacker to be on the same network segment as the target system (adjacent network access). Since UEFI firmware runs before the operating system loads, traditional endpoint security controls are ineffective at this stage, making this a particularly dangerous attack vector for network boot environments.

Successful exploitation can result in arbitrary code execution within the UEFI environment, allowing attackers to compromise the system before any operating system security measures are active. This could lead to persistent firmware-level malware, secure boot bypass, or complete system compromise.

Root Cause

The root cause is improper input validation (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer) in the DHCPv6 client implementation. The code fails to properly validate the length of the DNS Servers option before copying data into a fixed-size buffer, allowing an attacker-controlled overflow condition.

Attack Vector

The attack requires adjacent network access, meaning the attacker must be on the same network segment as the vulnerable system. The attack is executed by setting up a rogue DHCPv6 server that responds to DHCPv6 Solicit messages with maliciously crafted Advertise messages containing an oversized DNS Servers option.

The attack flow involves:

1. Target system initiates PXE boot and sends DHCPv6 Solicit message
2. Attacker's rogue DHCPv6 server responds with crafted Advertise message
3. Malicious DNS Servers option triggers buffer overflow in EDK2 firmware
4. Attacker achieves code execution in UEFI context

The vulnerability is exploitable without authentication or user interaction, and proof-of-concept code is publicly available through the PixieFail PoC collection.

Detection Methods for CVE-2023-45234

Indicators of Compromise

• Unexpected DHCPv6 traffic on network segments with PXE boot enabled
• Rogue DHCPv6 servers responding to client requests
• Anomalous DHCPv6 Advertise messages with unusually large DNS Servers options
• Systems failing to complete PXE boot or exhibiting unexpected behavior during network boot

Detection Strategies

• Deploy network monitoring to detect unauthorized DHCPv6 servers on boot network segments
• Implement DHCPv6 snooping on network switches to filter rogue DHCP responses
• Monitor for DHCPv6 packets with abnormally large option lengths
• Use network segmentation to isolate PXE boot traffic from untrusted network segments

Monitoring Recommendations

• Enable logging on authorized DHCPv6 servers to detect anomalous request patterns
• Implement network-based IDS/IPS rules to detect PixieFail exploitation attempts
• Monitor firmware integrity on critical systems using hardware security modules or TPM attestation
• Conduct regular network audits to identify unauthorized DHCP servers

How to Mitigate CVE-2023-45234

Immediate Actions Required

• Disable PXE/network boot on systems where it is not required
• Implement network segmentation to isolate boot networks from potentially hostile network segments
• Deploy DHCPv6 guard or snooping features on network infrastructure
• Update EDK2-based firmware to patched versions when available from system vendors

Patch Information

Tianocore has released security patches addressing this vulnerability. System administrators should consult their hardware vendor for firmware updates that incorporate the EDK2 fixes. Details are available in the GitHub Security Advisory.

Additional vendor-specific advisories:

• Fedora Package Announcement
• NetApp Security Advisory
• CERT Vulnerability Note

Workarounds

• Disable DHCPv6 in UEFI settings if IPv6 network boot is not required
• Use static IP configuration for network boot instead of DHCP
• Implement 802.1X port-based authentication on boot network segments
• Deploy network access control to prevent unauthorized devices from responding to DHCPv6 requests

# Example: Disable PXE boot in UEFI via efibootmgr (Linux)
# List current boot options
efibootmgr -v

# Remove network boot option (replace XXXX with actual boot number)
# efibootmgr -b XXXX -B

# Alternatively, configure network switches to block DHCPv6 from unauthorized sources
# Example Cisco IOS DHCPv6 guard configuration:
# ipv6 dhcp guard policy DHCP_GUARD
#   device-role server
#   trusted-port
# interface GigabitEthernet0/1
#   ipv6 dhcp guard attach-policy DHCP_GUARD