CVE-2023-40550 is a medium severity vulnerability identified in the Shim bootloader component of Red Hat Enterprise Linux 7. Shim is a small bootloader used to facilitate secure boot by validating signatures and ensuring trusted boot components. This vulnerability arises from an out-of-bounds read error during the validation of SBAT (Software Bill of Materials Attestation) information, a mechanism designed to attest the integrity and provenance of software components during boot. The out-of-bounds read can lead to exposure of sensitive memory contents during the early boot phase, potentially leaking confidential information. The flaw requires local access with low privileges (AV:L, PR:L) and does not require user interaction (UI:N). The vulnerability does not impact system integrity or availability but compromises confidentiality. The CVSS 3.1 vector (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N) reflects these characteristics. No public exploits or active exploitation have been reported to date. The vulnerability affects Red Hat Enterprise Linux 7 systems that use Shim for secure boot, which is common in enterprise and government environments. Since the flaw occurs during boot, it could be leveraged by an attacker with local access to extract sensitive data before the OS fully loads. This could include cryptographic keys or other protected information residing in memory. The vulnerability highlights the importance of secure boot components and their validation logic. Red Hat is expected to release patches to address this issue by correcting the bounds checking in the SBAT validation code. Until patches are applied, organizations should limit local access and monitor for suspicious activity. Given the nature of the flaw, remote exploitation is not feasible, reducing the immediate risk of widespread attacks.

The primary impact of CVE-2023-40550 is the potential exposure of sensitive data during the system boot process on affected Red Hat Enterprise Linux 7 systems. For European organizations, this could lead to leakage of confidential information such as cryptographic keys, secure boot parameters, or other protected memory contents, undermining the confidentiality of critical systems. Although the vulnerability does not affect system integrity or availability, the exposure of sensitive data could facilitate further attacks or unauthorized access if leveraged by malicious insiders or attackers with local access. Sectors with high security requirements, including government, finance, telecommunications, and critical infrastructure operators in Europe, may face increased risks if their RHEL 7 systems are unpatched. The requirement for local access and low privileges limits the attack surface but does not eliminate risk in environments where multiple users have access or where attackers have already gained limited footholds. The lack of known exploits reduces immediate threat levels but does not preclude future exploitation attempts. Overall, the vulnerability could weaken trust in secure boot mechanisms and complicate compliance with data protection regulations such as GDPR if sensitive data is exposed.

1. Apply official patches from Red Hat as soon as they become available to correct the out-of-bounds read in Shim's SBAT validation logic. 2. Restrict local access to Red Hat Enterprise Linux 7 systems to trusted and authorized personnel only, minimizing the risk of exploitation by low-privilege users. 3. Implement strict access controls and monitoring on systems that use Shim for secure boot, including auditing boot logs and access attempts. 4. Consider upgrading to newer supported versions of Red Hat Enterprise Linux where possible, as they may include improved secure boot components and security fixes. 5. Use hardware-based security features such as TPM (Trusted Platform Module) and secure boot policies to strengthen boot integrity and reduce attack vectors. 6. Educate system administrators about the vulnerability and the importance of securing the boot process and local access. 7. Employ endpoint detection and response (EDR) solutions to detect anomalous behavior that could indicate attempts to exploit boot-level vulnerabilities. 8. Review and limit the use of shared or multi-user systems running RHEL 7 to reduce exposure to local privilege exploitation.