CVE-2023-45237: Tianocore EDK2 Information Disclosure Flaw

CVE-2023-45237 Overview

CVE-2023-45237 is an insecure random number generation vulnerability affecting EDK2's Network Package. The vulnerability stems from the use of predictable TCP Initial Sequence Numbers (ISN), which can be exploited by network-based attackers to gain unauthorized access to sensitive information. This weakness in cryptographic randomness undermines the security guarantees that TCP connections are designed to provide.

Critical Impact

Attackers can predict TCP Initial Sequence Numbers, enabling TCP session hijacking, connection spoofing, and unauthorized access leading to potential loss of confidentiality.

Affected Products

• Tianocore EDK2 (all versions with vulnerable Network Package)
• Systems using EDK2-based UEFI firmware with network functionality
• Enterprise servers and embedded devices utilizing EDK2 network stack

Discovery Timeline

• 2024-01-16 - CVE-2023-45237 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2023-45237

Vulnerability Analysis

This vulnerability falls under CWE-338 (Use of Cryptographically Weak Pseudo-Random Number Generator). EDK2's Network Package generates TCP Initial Sequence Numbers using a predictable algorithm, which violates the fundamental security assumptions of TCP protocol design. The ISN is meant to be unpredictable to prevent attackers from injecting packets into legitimate TCP streams or hijacking connections.

When the ISN generation is predictable, an attacker positioned on the network can observe a sequence of connections, deduce the algorithm's state, and predict future sequence numbers. This enables various attack scenarios including TCP session hijacking, blind TCP injection attacks, and connection reset attacks.

The vulnerability is exploitable remotely without requiring authentication or user interaction, making it particularly concerning for systems that rely on EDK2's network stack in pre-boot environments or embedded systems where firmware-level networking is utilized.

Root Cause

The root cause is the use of a cryptographically weak pseudo-random number generator (PRNG) for generating TCP Initial Sequence Numbers in EDK2's Network Package. Instead of using a cryptographically secure random number source, the implementation relies on predictable values that can be reverse-engineered by observing network traffic patterns.

RFC 6528 specifies requirements for TCP ISN generation to prevent sequence number prediction attacks. The EDK2 implementation fails to meet these security requirements, using an algorithm that does not provide sufficient entropy or unpredictability.

Attack Vector

The attack is network-based and can be executed by an attacker who can observe TCP connections originating from the vulnerable system. The attack flow typically involves:

1. Observation Phase: The attacker monitors TCP connections from the target system to capture Initial Sequence Numbers
2. Analysis Phase: By collecting multiple ISN samples, the attacker identifies patterns and reverse-engineers the PRNG state
3. Prediction Phase: Using the recovered state, the attacker predicts future ISNs for new connections
4. Exploitation Phase: The attacker uses predicted ISNs to hijack sessions, inject malicious data, or impersonate legitimate endpoints

The attack does not require any privileges on the target system and can be performed by any attacker with network visibility to the vulnerable system's TCP traffic.

Detection Methods for CVE-2023-45237

Indicators of Compromise

• Unexpected TCP connection resets or anomalies in network traffic patterns
• Suspicious packet injection attempts with accurate sequence number predictions
• Network traffic analysis showing predictable ISN patterns across multiple connections
• Evidence of man-in-the-middle positioning or ARP spoofing attacks preceding TCP hijacking

Detection Strategies

• Deploy network intrusion detection systems (NIDS) configured to detect TCP sequence number anomalies
• Implement statistical analysis of ISN values to identify predictable generation patterns
• Monitor for unexpected session terminations or data integrity failures in critical connections
• Conduct periodic firmware version audits to identify systems running vulnerable EDK2 versions

Monitoring Recommendations

• Enable comprehensive network flow logging for systems using EDK2 network stack
• Configure alerts for TCP sessions with unusual packet injection or reset patterns
• Implement network segmentation to limit attacker visibility of vulnerable system traffic
• Establish baseline TCP connection patterns to detect deviations indicative of exploitation

How to Mitigate CVE-2023-45237

Immediate Actions Required

• Inventory all systems utilizing EDK2-based firmware with network functionality
• Apply firmware updates from system vendors that include patched EDK2 Network Package
• Implement network segmentation to isolate systems with vulnerable firmware
• Consider disabling firmware-level networking if not operationally required until patches are applied

Patch Information

Tianocore has released security advisories addressing this vulnerability. Organizations should consult the GitHub Advisory for EDK2 for detailed patch information. System vendors (OEMs) incorporating EDK2 should release firmware updates integrating the fix.

Additional advisories are available from NetApp Security Advisory and CERT Vulnerability Report for affected enterprise products.

Workarounds

• Deploy network encryption (IPsec, TLS) at higher layers to mitigate confidentiality impact
• Implement strict network access controls to limit attacker visibility of vulnerable systems
• Use network monitoring to detect and block potential exploitation attempts
• Consider hardware-based security solutions that provide cryptographically secure random numbers

For environments where firmware updates cannot be immediately applied, network-level compensating controls provide defense-in-depth while the underlying vulnerability remains. Consult the Openwall OSS Security Post for additional technical guidance on mitigation strategies.