CVE-2024-21399 is a high-severity use-after-free vulnerability (CWE-416) identified in the Chromium-based Microsoft Edge browser. This vulnerability allows remote code execution (RCE) if exploited successfully. The flaw arises from improper handling of memory within the browser, where an object is freed but later accessed, leading to undefined behavior that attackers can leverage to execute arbitrary code. The vulnerability is remotely exploitable over the network without requiring privileges but does require user interaction, such as visiting a malicious website or opening a crafted link. The CVSS 3.1 base score is 8.3, reflecting high impact on confidentiality, integrity, and availability, with a complexity rated as high due to the need for user interaction and some attack complexity. The scope is changed (S:C), meaning the vulnerability can affect components beyond the initially vulnerable component, increasing the potential impact. Although no known exploits are currently reported in the wild, the vulnerability's nature and Microsoft Edge's widespread use make it a significant threat vector. The vulnerability affects version 1.0.0 of Microsoft Edge Chromium-based, which likely refers to early or specific builds, but given Edge's auto-update mechanism, later versions may also be impacted if not patched. No patch links are provided yet, indicating that mitigation may rely on forthcoming updates or workarounds.

For European organizations, this vulnerability poses a substantial risk due to the widespread adoption of Microsoft Edge as a default or preferred browser in corporate and governmental environments. Successful exploitation could lead to remote code execution, allowing attackers to take full control of affected systems, steal sensitive data, disrupt operations, or deploy further malware. The high impact on confidentiality, integrity, and availability means that critical services, intellectual property, and personal data could be compromised. Given the browser's role as a gateway to the internet and internal resources, exploitation could serve as a foothold for lateral movement within networks. The requirement for user interaction (e.g., visiting a malicious website) means phishing or social engineering campaigns could be effective attack vectors. European organizations handling sensitive data under GDPR and other regulations face potential compliance and reputational risks if exploited. The absence of known exploits currently provides a window for proactive mitigation, but the threat landscape could evolve rapidly.

European organizations should prioritize the following specific actions: 1) Immediately verify the Microsoft Edge version in use across all endpoints and servers, focusing on those running version 1.0.0 or unpatched variants. 2) Apply the latest security updates from Microsoft as soon as they become available; monitor Microsoft security advisories closely. 3) Implement strict browser security policies, including disabling or restricting JavaScript execution on untrusted sites, using browser isolation technologies, and enforcing strict content security policies. 4) Enhance email and web filtering to block or flag suspicious links and attachments that could trigger user interaction leading to exploitation. 5) Conduct targeted user awareness training emphasizing the risks of clicking unknown links or visiting untrusted websites. 6) Employ endpoint detection and response (EDR) solutions to monitor for unusual browser behavior indicative of exploitation attempts. 7) Consider deploying network-level protections such as web proxies with advanced threat detection to intercept malicious traffic. 8) Maintain robust backup and incident response plans to quickly recover if exploitation occurs. These measures go beyond generic advice by focusing on version control, user behavior, and layered defenses tailored to the exploitation method.