CVE-2023-40549 is a medium-severity vulnerability identified in Shim, a component used in the boot process of Red Hat Enterprise Linux 7. The flaw arises from an out-of-bounds read caused by insufficient boundary checks when loading Portable Executable (PE) binaries. Specifically, Shim fails to properly verify the size and structure of a PE binary before processing it, allowing an attacker to craft a malicious PE binary that triggers an out-of-bounds read. This results in Shim crashing, which leads to a denial of service (DoS) condition during the boot or secure boot process. The vulnerability does not allow for code execution or data leakage, but it impacts system availability by preventing normal boot operations. The attack vector is local, meaning an attacker must have local access to the system to supply the malicious PE binary. No privileges or user interaction are required, which lowers the barrier for exploitation once local access is obtained. The CVSS v3.1 base score is 6.2, reflecting the medium severity due to the impact on availability and the ease of exploitation without privileges. No known exploits have been reported in the wild, and no patches were linked in the provided information, but it is expected that Red Hat will release updates to address this issue. Organizations running Red Hat Enterprise Linux 7, particularly those relying on secure boot mechanisms involving Shim, should be aware of this vulnerability and prepare to apply patches promptly.

The primary impact of CVE-2023-40549 is a denial of service condition caused by Shim crashing when processing a crafted PE binary. For European organizations, this could lead to system unavailability, particularly in environments where Red Hat Enterprise Linux 7 is used in critical infrastructure, servers, or embedded systems relying on secure boot. The inability to boot or maintain system uptime could disrupt business operations, especially in sectors such as finance, healthcare, telecommunications, and government services. Since the vulnerability requires local access, the risk is higher in environments with multiple users or where attackers can gain physical or remote local access. Although confidentiality and integrity are not directly affected, the availability impact can have cascading effects on service delivery and operational continuity. Organizations using legacy systems or those slow to upgrade from RHEL 7 may face prolonged exposure. The lack of known exploits reduces immediate risk, but the medium severity score indicates that exploitation could be impactful if attackers gain local access.

1. Monitor Red Hat advisories closely and apply official patches or updates for Shim as soon as they are released to remediate the vulnerability. 2. Restrict local system access to trusted and authenticated users only, using strong access controls and physical security measures to prevent unauthorized local access. 3. Implement strict user account management and privilege separation to minimize the risk of unprivileged users exploiting the flaw. 4. Employ system integrity monitoring and logging to detect abnormal Shim crashes or boot failures that could indicate exploitation attempts. 5. Consider upgrading to a newer Red Hat Enterprise Linux version where this vulnerability is not present or has been fixed, reducing exposure to legacy vulnerabilities. 6. In environments where secure boot is critical, validate the integrity of PE binaries before loading them, if feasible, to prevent crafted binaries from triggering the flaw. 7. Conduct regular security audits and penetration testing focusing on local privilege escalation and denial of service vectors to identify and mitigate related risks.