CVE-2024-38433 Overview
CVE-2024-38433 is an authentication bypass vulnerability (CWE-305) affecting Nuvoton NPCM7xx Baseboard Management Controller (BMC) subsystems. An attacker with write access to the SPI-Flash can modify the u-boot image header on flash that is parsed by the BootBlock reference code, potentially leading to arbitrary code execution at the firmware level.
This vulnerability targets the boot process of BMC systems, which are critical components used for remote server management in data centers and enterprise environments. The BootBlock's failure to properly authenticate the u-boot image header before parsing allows attackers to inject malicious code that executes during the boot sequence.
Critical Impact
Attackers with SPI-Flash write access can achieve arbitrary code execution on Nuvoton NPCM7xx BMC subsystems by manipulating the u-boot image header, potentially compromising server management infrastructure.
Affected Products
- Nuvoton NPCM750R Firmware
- Nuvoton NPCM730R Firmware
- Nuvoton NPCM710R Firmware
- Nuvoton NPCM705R Firmware
- Nuvoton NPCM750R Hardware
- Nuvoton NPCM730R Hardware
- Nuvoton NPCM710R Hardware
- Nuvoton NPCM705R Hardware
Discovery Timeline
- July 11, 2024 - CVE-2024-38433 published to NVD
- November 21, 2024 - Last updated in NVD database
Technical Details for CVE-2024-38433
Vulnerability Analysis
CVE-2024-38433 represents an authentication bypass vulnerability in the boot chain of Nuvoton NPCM7xx BMC processors. The vulnerability exists in the BootBlock reference code, which fails to properly validate the integrity and authenticity of the u-boot image header stored on SPI-Flash memory before parsing it.
BMC (Baseboard Management Controller) systems are embedded controllers used for out-of-band server management, providing administrators with remote access to servers regardless of the operating system state. The NPCM7xx series is Nuvoton's second-generation BMC solution designed for server platforms.
During the boot process, the BootBlock reads and parses the u-boot image header from SPI-Flash to determine how to load and execute the u-boot bootloader. The lack of proper authentication on this header allows an attacker who has gained write access to the SPI-Flash to modify critical fields, redirecting execution to attacker-controlled code.
Root Cause
The root cause of this vulnerability is the absence of proper authentication mechanisms (CWE-305: Authentication Bypass by Primary Weakness) in the BootBlock reference code. The code trusts the u-boot image header data read from SPI-Flash without verifying its cryptographic signature or integrity. This primary weakness in authentication allows the boot chain to be compromised.
Additionally, the vulnerability is classified under CWE-287 (Improper Authentication), as the system fails to prove that a claimed entity or data is authentic before proceeding with critical boot operations.
Attack Vector
The attack requires local access with high privileges to write to the SPI-Flash storage on the target system. An attacker must first obtain write access to the SPI-Flash, which could be achieved through:
- Physical access to the hardware to directly interface with the SPI-Flash chip
- Exploiting another vulnerability that grants flash write permissions
- Compromising administrative credentials for the BMC interface
- Supply chain attacks during manufacturing or maintenance
Once write access is obtained, the attacker can modify the u-boot image header fields that control the boot process. The BootBlock parses these header fields without authentication, allowing the attacker to redirect code execution to malicious payloads stored elsewhere on the flash or to corrupt the boot process in ways that facilitate further exploitation.
The attack mechanism involves manipulating header fields such as entry point addresses, image sizes, or load addresses to cause the BootBlock to load and execute arbitrary code. Since this occurs early in the boot sequence, the attacker gains control before higher-level security mechanisms are initialized.
Detection Methods for CVE-2024-38433
Indicators of Compromise
- Unexpected modifications to SPI-Flash contents, particularly in the u-boot image header region
- Changes to firmware checksums or hash values during integrity verification
- Anomalous BMC behavior during boot sequences or unexpected boot failures
- Unauthorized access attempts to flash programming interfaces
Detection Strategies
- Implement firmware integrity monitoring to detect unauthorized modifications to SPI-Flash contents
- Enable and monitor secure boot logs for authentication failures or unexpected boot paths
- Deploy hardware security modules that can verify flash contents before boot
- Monitor BMC access logs for unauthorized administrative access that could precede flash modification
Monitoring Recommendations
- Establish baseline firmware hashes and regularly verify SPI-Flash contents against known-good values
- Configure alerts for any access to flash programming interfaces or utilities
- Monitor physical access to server hardware that could indicate tampering attempts
- Implement continuous monitoring of BMC health and configuration status
How to Mitigate CVE-2024-38433
Immediate Actions Required
- Review and restrict access to SPI-Flash write capabilities on affected NPCM7xx systems
- Implement hardware write protection for SPI-Flash where possible
- Audit BMC administrative access and credentials to prevent unauthorized flash modifications
- Monitor affected systems for signs of firmware tampering
Patch Information
Organizations using affected Nuvoton NPCM7xx BMC subsystems should consult the Israeli Government CVE Advisories for official guidance and updates. Contact Nuvoton directly or through your server OEM vendor for updated BootBlock reference code that includes proper u-boot image header authentication.
When patching, ensure that:
- Firmware updates are obtained from verified vendor sources
- Updates are cryptographically verified before installation
- Post-update verification confirms the patch was applied correctly
Workarounds
- Enable hardware write-protect jumpers or pins on SPI-Flash chips if available on your hardware platform
- Restrict physical access to servers containing affected BMC hardware
- Implement network segmentation to isolate BMC management interfaces from untrusted networks
- Disable unused BMC interfaces and features to reduce attack surface
- Consider implementing an external trusted platform module (TPM) to verify boot integrity
# Example: Check SPI-Flash write protection status (platform-specific)
# Verify your hardware documentation for specific commands
flashrom -p internal --wp-status
# Enable write protection if supported (example only - verify for your platform)
flashrom -p internal --wp-enable
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
