CVE-2023-45236: Tianocore EDK2 Information Disclosure Flaw

CVE-2023-45236 Overview

CVE-2023-45236 is a vulnerability in EDK2's Network Package that involves predictable TCP Initial Sequence Numbers (ISN). The EDK2 (EFI Development Kit II) is the open-source reference implementation of UEFI firmware maintained by Tianocore. This vulnerability stems from the use of insecure random number generation for TCP sequence numbers, which can be exploited by network-based attackers to predict sequence numbers and potentially hijack TCP connections or gain unauthorized access to confidential data.

Critical Impact

Attackers can exploit predictable TCP Initial Sequence Numbers to potentially hijack network connections, leading to unauthorized access and loss of confidentiality in UEFI firmware environments.

Affected Products

• Tianocore EDK2 (all versions with vulnerable Network Package)
• Systems utilizing EDK2-based UEFI firmware with network stack enabled
• Enterprise and embedded devices running affected EDK2 implementations

Discovery Timeline

• 2024-01-16 - CVE-2023-45236 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2023-45236

Vulnerability Analysis

This vulnerability affects the TCP/IP stack implementation within EDK2's Network Package. The core issue lies in the generation of TCP Initial Sequence Numbers, which are intended to be unpredictable to prevent TCP session hijacking attacks. When sequence numbers are predictable, an attacker can forge TCP packets that appear legitimate to the receiving system.

The vulnerability is classified under CWE-338 (Use of Cryptographically Weak Pseudo-Random Number Generator) and CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). The weak random number generation allows attackers to calculate or predict the ISN values that will be used for new TCP connections, enabling various network-based attacks.

This is particularly concerning in firmware environments where the UEFI network stack may be used during pre-boot operations, PXE boot scenarios, or firmware update processes over the network.

Root Cause

The root cause of CVE-2023-45236 is the use of a cryptographically weak pseudo-random number generator (PRNG) for generating TCP Initial Sequence Numbers in EDK2's Network Package. TCP connections rely on unpredictable ISN values as a security measure against blind injection attacks. When the PRNG is weak or predictable, the security guarantees of TCP are undermined, allowing attackers to:

1. Predict future sequence numbers for new connections
2. Inject malicious packets into established sessions
3. Hijack TCP connections to intercept or manipulate data

Attack Vector

The attack vector is network-based and can be exploited remotely without requiring authentication or user interaction. An attacker positioned on the network path (or capable of spoofing source addresses) can:

1. Observe TCP connections from the vulnerable system to analyze ISN patterns
2. Use statistical analysis to predict future ISN values based on the weak PRNG
3. Initiate connection hijacking or blind injection attacks using predicted sequence numbers
4. Potentially intercept confidential data or inject malicious commands during firmware operations

The vulnerability exploitation mechanism involves analyzing the algorithm used for ISN generation and exploiting its predictability. Rather than providing synthetic exploit code, the technical details of the ISN prediction methodology can be found in the CERT Vulnerability Advisory and the GitHub Security Advisory.

Detection Methods for CVE-2023-45236

Indicators of Compromise

• Anomalous TCP connection patterns with sequential or predictable ISN values observed in network traffic
• Unexpected TCP RST packets indicating potential session hijacking attempts
• Network traffic anomalies during UEFI/firmware operations such as PXE boot or firmware updates
• Evidence of spoofed packets targeting systems during pre-boot network operations

Detection Strategies

• Implement network traffic analysis to detect TCP connections with predictable ISN patterns
• Deploy network intrusion detection systems (NIDS) with rules to identify ISN prediction attack patterns
• Monitor firmware update and PXE boot traffic for signs of tampering or injection
• Audit systems to identify EDK2-based firmware versions in the environment

Monitoring Recommendations

• Enable detailed logging for network operations during UEFI/firmware stages where possible
• Implement network segmentation to isolate pre-boot and firmware management traffic
• Monitor for advisory updates from Tianocore, NetApp, and other affected vendors
• Conduct periodic firmware audits to track EDK2 versions deployed across the infrastructure

How to Mitigate CVE-2023-45236

Immediate Actions Required

• Review the Tianocore GitHub Security Advisory for patch availability and affected versions
• Identify all systems in your environment using EDK2-based UEFI firmware with network capabilities
• Prioritize patching for systems that perform network operations during pre-boot (PXE boot, firmware updates over network)
• Implement network segmentation to reduce exposure of vulnerable systems during firmware operations

Patch Information

Tianocore has released a security advisory addressing this vulnerability. Organizations should consult the GitHub Security Advisory GHSA-hc6x-cw6p-gj7h for specific patch information and updated EDK2 versions. Additionally, the NetApp Security Advisory NTAP-20240307-0011 provides guidance for NetApp products affected by this vulnerability.

Firmware updates should be obtained from device manufacturers who incorporate EDK2 into their UEFI implementations. Coordinate with hardware vendors to determine when patched firmware versions will be available for specific platforms.

Workarounds

• Disable network boot (PXE) functionality where not required to reduce the attack surface
• Isolate firmware management networks from untrusted network segments
• Use out-of-band management channels for firmware updates instead of in-band network methods
• Implement strict network access controls for systems during UEFI/pre-boot operations

Mitigation strategies for this vulnerability focus primarily on network isolation and reducing the use of network functionality during firmware operations. As this is a firmware-level vulnerability, configuration-based mitigations are limited. The recommended approach is to apply firmware updates from device manufacturers as they become available and minimize network exposure during pre-boot operations until patches can be deployed.