CVE-2024-26256 is a high-severity heap-based buffer overflow vulnerability (CWE-122) affecting Microsoft Windows 11 version 22H2 (build 10.0.22621.0). The vulnerability resides within the Libarchive component or functionality integrated into Windows 11, which is responsible for handling archive files. A heap-based buffer overflow occurs when data exceeding the allocated buffer size is written to the heap memory, potentially overwriting adjacent memory and leading to arbitrary code execution. This vulnerability allows a remote attacker to execute code on the affected system by convincing a user to open or interact with a specially crafted archive file. The CVSS 3.1 base score is 7.8, indicating high severity, with the vector string CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C. This means the attack requires local access (AV:L), low attack complexity (AC:L), no privileges (PR:N), but user interaction (UI:R) is necessary. The scope is unchanged (S:U), and the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). The exploitability level is not currently known to be exploited in the wild, and no patches have been linked yet. The vulnerability was reserved in February 2024 and published in April 2024. Given the nature of the vulnerability, successful exploitation could allow an attacker to execute arbitrary code with the privileges of the user opening the malicious archive, potentially leading to full system compromise if the user has elevated rights. The requirement for user interaction limits remote exploitation but remains a significant risk, especially in environments where users frequently handle archive files from untrusted sources.

For European organizations, this vulnerability poses a significant risk, particularly in sectors where Windows 11 22H2 adoption is high and where users regularly handle archive files, such as finance, government, healthcare, and critical infrastructure. Exploitation could lead to unauthorized disclosure of sensitive data, system integrity compromise, and denial of service. The high impact on confidentiality, integrity, and availability means that attackers could steal data, install persistent malware, or disrupt operations. The requirement for user interaction suggests phishing or social engineering campaigns could be effective attack vectors. Organizations with remote or hybrid workforces are especially vulnerable due to increased exposure to potentially malicious files received via email or cloud services. The lack of known exploits in the wild currently provides a window for proactive mitigation, but the high severity score indicates that once exploits emerge, the threat could escalate rapidly. Additionally, the absence of an official patch at the time of publication increases the urgency for interim protective measures.

1. Implement strict email and file filtering policies to block or quarantine archive files from untrusted or unknown sources. 2. Educate users about the risks of opening archive files from unverified senders and encourage verification before extraction. 3. Employ endpoint detection and response (EDR) solutions capable of monitoring and blocking suspicious archive file activities and heap-based memory corruption attempts. 4. Use application whitelisting to restrict execution of unauthorized or unknown applications that could be dropped or executed via malicious archives. 5. Enable and enforce the use of least privilege principles to limit the impact of any successful exploitation, ensuring users operate with minimal necessary rights. 6. Monitor security advisories from Microsoft closely and prepare for rapid deployment of patches once available. 7. Consider disabling or restricting the use of Libarchive-related features or archive file handling in critical environments until patches are released. 8. Implement network segmentation to limit lateral movement in case of compromise. 9. Use sandboxing or virtualized environments for opening suspicious archive files where possible.