CVE-2023-40548 is a heap-based buffer overflow vulnerability found in the Shim bootloader component of Red Hat Enterprise Linux 7 on 32-bit architectures. Shim is responsible for loading and verifying boot components, including PE binaries used in the UEFI Secure Boot process. The vulnerability occurs due to an addition operation involving a user-controlled value parsed from a PE binary, which is then used for memory allocation without proper bounds checking. This leads to an out-of-bounds write in the heap, causing memory corruption. The corrupted memory can result in system crashes or data integrity issues during the boot phase, potentially allowing an attacker to disrupt system availability or compromise the boot process integrity. The CVSS v3.1 score of 7.4 reflects a high severity, with an attack vector limited to local access (AV:L), high attack complexity (AC:H), no privileges required (PR:N), and no user interaction (UI:N). The scope remains unchanged (S:U), but the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). No known exploits are currently reported in the wild, but the vulnerability poses a significant risk to systems using 32-bit RHEL 7 with Shim. The lack of patch links suggests that remediation may require vendor updates or configuration changes. Organizations relying on this platform should assess their exposure and implement mitigations to prevent exploitation during the boot process.

For European organizations, the impact of CVE-2023-40548 is significant, especially for those using 32-bit Red Hat Enterprise Linux 7 systems in critical environments such as government, finance, healthcare, and industrial control systems. Exploitation can lead to denial of service through system crashes during boot or potentially allow attackers to compromise the integrity of the boot process, undermining system trustworthiness. This could result in prolonged downtime, loss of data integrity, and increased risk of persistent malware infections if the boot process is subverted. Given the high confidentiality impact, sensitive data could be exposed or manipulated if attackers gain control over the boot sequence. The requirement for local access and high attack complexity somewhat limits the threat to insiders or attackers with physical or administrative access, but the absence of required privileges or user interaction means that once local access is obtained, exploitation is feasible. European organizations with legacy 32-bit RHEL 7 deployments should consider the risk of operational disruption and potential compliance implications under regulations such as GDPR if data integrity or availability is compromised.

1. Apply official patches from Red Hat as soon as they become available to address the buffer overflow in Shim. 2. Restrict physical and local access to systems running 32-bit RHEL 7 to trusted personnel only, reducing the risk of local exploitation. 3. Implement strict boot media controls and secure boot policies to prevent unauthorized or malicious PE binaries from being loaded during the boot process. 4. Where possible, migrate from 32-bit to 64-bit architectures and upgrade to supported Red Hat Enterprise Linux versions to reduce exposure to legacy vulnerabilities. 5. Employ runtime integrity verification tools that monitor bootloader and kernel integrity to detect anomalies caused by exploitation attempts. 6. Conduct regular audits of boot configurations and verify the authenticity of boot components to ensure no tampering has occurred. 7. Use hardware-based security features such as TPM and UEFI Secure Boot with strict enforcement to mitigate unauthorized boot modifications. 8. Develop incident response plans that include boot-level compromise scenarios to quickly isolate and remediate affected systems.