The Devastating PixieFail Flaws in UEFI – Is Your Device at Risk?

The recent discovery of “PixieFail,” a set of nine vulnerabilities in Tianocore’s EDK II IPv6 network stack, has raised significant concerns in the cybersecurity community. These vulnerabilities are critical as they affect the Preboot eXecution Environment (PXE) network boot process, a common feature in enterprise systems.

The vulnerabilities were discovered by security researchers at Quarkslab. They primarily affect the network stack of EDK II, potentially allowing attackers to execute arbitrary code during the network boot process. The vulnerabilities range from buffer overflows to improper input validation, each presenting unique risks and exploitation scenarios. PXE is widely used for remote booting and system management in enterprise networks. The vulnerabilities in the IPv6 network stack could allow attackers to compromise systems during the boot process, posing a significant threat to organizational security.

The Preboot Execution Environment (PXE) is a standardized client-server interface that allows computers to boot up and load an operating system (OS) from a network server rather than from a local storage device like a hard drive or SSD. PXE is particularly useful in environments where it’s necessary to boot multiple systems with the same configuration or to boot systems without a dedicated storage device.

How PXE Works:

1. Initialization:
   • When a computer equipped with PXE firmware starts up, it initializes its network interface and contacts a server on the network using the Dynamic Host Configuration Protocol (DHCP).
2. DHCP and IP Address Allocation:
   • The DHCP server assigns an IP address to the PXE-enabled client and also provides the location of the boot server (a server that contains the bootable files).
3. Boot Server and Boot File:
   • The boot server is typically a Trivial File Transfer Protocol (TFTP) server. The DHCP server tells the PXE client the address of the TFTP server and the name of a Network Bootstrap Program (NBP) file to be downloaded.
4. Downloading NBP:
   • The PXE client then contacts the TFTP server, downloads the NBP file, and executes it. This NBP is a small piece of software, often a basic OS or a bootloader, which will then start the process of loading the full operating system.
5. Loading the Operating System:
   • After the NBP is executed, it may download additional components or the entire OS image from the network, depending on the configuration. This can be done using TFTP or other protocols like HTTP or iSCSI.
6. OS Boot-Up:
   • Once the necessary components are downloaded, the NBP hands over control to the OS, which continues booting up as it normally would from a local storage device.

Example Scenario:

Imagine a company with a large number of workstations that need to be regularly updated with new software or reconfigured. Instead of manually updating each machine, the company uses PXE to boot the workstations from a central server.

• Server Setup: The company sets up a TFTP server with the required OS images and configurations.
• Workstation Boot-Up: Each workstation is PXE-enabled. When a workstation is booted, it sends a request to the DHCP server.
• DHCP Response: The DHCP server assigns an IP address to the workstation and provides the location of the TFTP server and the NBP file.
• OS Loading: The workstation downloads the NBP from the TFTP server, which in turn loads the necessary OS and software configurations directly from the server.
• Operational Workstation: The workstation is now up and running with the latest configuration, without requiring any local storage for the OS.

Advantages of PXE:

• Centralized Management: Allows centralized control and deployment of OS and software, simplifying management and updates.
• Cost-Effective: Reduces the need for local storage on each client machine.
• Flexibility: Enables quick reconfiguration or re-imaging of systems in a networked environment.
• Scalability: Ideal for large organizations where deploying and maintaining multiple systems is routine.

Limitations:

• Network Dependency: Relies heavily on the network infrastructure. Network issues can prevent systems from booting.
• Security Concerns: The booting process can be vulnerable to attacks, such as rogue DHCP servers or unauthorized access to the network.

PXE is widely used in enterprise environments, data centers, and for remote workstation management, offering a streamlined and efficient way to manage multiple systems.

The blog post from Quarkslab provides detailed information about the nine vulnerabilities affecting the IPv6 network protocol stack of EDK II, TianoCore’s open-source reference implementation of UEFI. Here’s a summary of each vulnerability:

1. CVE-2023-45229: Integer Underflow in DHCPv6 Advertise Message Processing
   • This vulnerability is caused by a lack of sanity checks for IA_NA and IA_TA options in DHCPv6 Advertise messages. It can lead to an integer underflow, allowing attackers to read memory past the end of the received packet.
2. CVE-2023-45230: Buffer Overflow via Long Server ID Option in DHCPv6 Client
   • This issue arises when handling the Server ID option in DHCPv6 Request messages. An overly large Length field in the Server ID option can overflow a buffer with controlled data, leading to potential remote code execution.
3. CVE-2023-45231: Out of Bounds Read in ND Redirect Message Handling
   • This vulnerability occurs in the handling of Neighbor Discovery (ND) protocol’s Redirect messages. A single-byte truncated option in the options section of an ND Redirect message can cause an out-of-bounds read.
4. CVE-2023-45232: Infinite Loop in Parsing Unknown Options in Destination Options Header
   • This issue is found in the Ip6IsExtsValid function, which validates extension headers in IPv6 packets. An infinite loop can be triggered when parsing unknown options in the Destination Options header.
5. CVE-2023-45233: Infinite Loop in Parsing a PadN Option in Destination Options Header
   • Similar to CVE-2023-45232, this vulnerability leads to an infinite loop in the Ip6IsOptionValid function when parsing a PadN option with a specific length field value.
6. CVE-2023-45234: Buffer Overflow in Processing DNS Servers Option in DHCPv6 Advertise Message
   • This vulnerability is due to improper handling of the OPTION_DNS_SERVERS option length in DHCPv6 offers. A buffer overflow can occur if the option length is shorter than expected.
7. CVE-2023-45235: Buffer Overflow in Handling Server ID Option from DHCPv6 Proxy Advertise Message
   • This issue arises in the PxeBcRequestBootService function when handling the Server ID option from a DHCPv6 proxy Advertise message. It can lead to a buffer overflow.
8. CVE-2023-45236: Vulnerability in DHCPv6 Relay Forward Message Handling
   • This vulnerability involves the handling of DHCPv6 Relay Forward messages. Specific details about the nature of this vulnerability, such as whether it leads to buffer overflow, information disclosure, or another type of security risk, were not provided in the extracted content. However, it likely involves improper processing or validation of these messages, which could be exploited under certain conditions.
9. CVE-2023-45237: Weakness in Pseudorandom Number Generator
   • This vulnerability is related to a weakness in the pseudorandom number generator used in the network stack. The specific impact of this vulnerability could range from reduced cryptographic strength to potential predictability in functions relying on randomness. This could have implications for security features that depend on random number generation for their effectiveness.

The exploitation of these vulnerabilities could lead to unauthorized access, data breaches, and disruption of critical enterprise operations.

The PixieFail vulnerabilities in Tianocore’s EDK II IPv6 network stack affect several vendors who use the EDK II’s NetworkPkg module. Here is a list of the affected vendors as mentioned in the Quarkslab blog post:

1. Tianocore
   • Specifically, the vulnerabilities are present in the EDK II UEFI implementation developed and maintained by Tianocore.
2. Arm Ltd.
   • Affected through their Arm reference solutions.
3. Insyde Software
   • Their Insyde H20 UEFI BIOS is impacted.
4. American Megatrends Inc. (AMI)
   • The vulnerabilities affect AMI’s Aptio OpenEdition.
5. Phoenix Technologies Inc.
   • Their SecureCore technology is also impacted.
6. Microsoft Corporation
   • The vulnerabilities affect Microsoft’s Project Mu.

Additionally, the CERT/CC published Vulnerability Note VU#132380 provides a more comprehensive list of affected vendors, along with guidance to deploy fixes and mitigations.

Community Response and Discussion

• The cybersecurity community on platforms like Reddit has been actively discussing the technical aspects and potential mitigation strategies for PixieFail. Security experts emphasize the need for prompt patching and revisiting network security protocols to safeguard against such vulnerabilities.

Official Statements and Recommendations

• Tianocore has acknowledged the vulnerabilities and released patches to address them.
• Security Recommendations: Organizations are advised to update their systems with the latest patches and conduct thorough security audits to identify any potential exploitation of these vulnerabilities.

Broader Implications for Network Security

• Analysis: The discovery of PixieFail underscores the ongoing challenges in securing network protocols and firmware components.
• Future Outlook: This incident highlights the need for continuous vigilance, regular security updates, and proactive threat detection mechanisms in enterprise networks.

PixieFail represents a critical reminder of the vulnerabilities that can exist in foundational network components like the EDK II IPv6 stack. The swift identification and patching of these vulnerabilities are commendable, but they also serve as a call to action for the cybersecurity community to remain alert and proactive in identifying and mitigating such threats.