CVE-2019-0991 is a remote code execution (RCE) vulnerability found in the Chakra scripting engine used by the EdgeHTML-based version of Microsoft Edge browser. The vulnerability arises from improper handling of objects in memory, which can lead to memory corruption. An attacker exploiting this flaw can execute arbitrary code within the security context of the current user. If the user has administrative privileges, the attacker could gain full control over the affected system, enabling them to install software, modify or delete data, or create new user accounts with elevated rights. The attack vector is primarily web-based: an attacker can host a malicious website crafted to exploit this vulnerability or leverage compromised or user-content-accepting websites to deliver the exploit. Successful exploitation requires user interaction, specifically convincing the user to visit the malicious or compromised website using the vulnerable EdgeHTML-based Microsoft Edge browser. The vulnerability was addressed by Microsoft through a security update that modifies how the Chakra engine manages objects in memory to prevent corruption. The CVSS v3.1 base score is 4.2, reflecting a medium severity level, with attack vector as network, high attack complexity, no privileges required, user interaction required, and partial impact on confidentiality and integrity but no impact on availability. No known exploits in the wild have been reported, and the vulnerability affects all versions of the EdgeHTML-based Microsoft Edge browser up to the time of the patch release in June 2019.

For European organizations, the impact of CVE-2019-0991 depends on the extent of EdgeHTML-based Microsoft Edge usage within their environments. Organizations relying on this browser version, especially those with users having administrative privileges, face risks of unauthorized code execution leading to potential system compromise. This could result in data breaches, unauthorized access to sensitive information, disruption of business processes, and potential lateral movement within networks. Since the attack requires user interaction via web browsing, phishing or social engineering campaigns could be used to lure users to malicious sites. Given the medium severity and the requirement for user interaction, the threat is moderate but still significant, particularly for sectors with high-value data or critical infrastructure. Additionally, organizations that have not applied the relevant security updates remain vulnerable. The lack of known exploits in the wild reduces immediate risk but does not eliminate the possibility of future exploitation. European organizations must consider this vulnerability in their patch management and endpoint security strategies to prevent potential exploitation.

1. Apply the official Microsoft security update that addresses CVE-2019-0991 promptly to all systems running the EdgeHTML-based Microsoft Edge browser. 2. Where possible, transition users to the Chromium-based Microsoft Edge browser or alternative modern browsers that do not use the vulnerable Chakra engine. 3. Implement strict web filtering and URL reputation services to block access to known malicious or suspicious websites that could host exploit code. 4. Educate users about the risks of visiting untrusted websites and the importance of cautious browsing behavior to reduce the likelihood of successful social engineering attacks. 5. Employ endpoint detection and response (EDR) solutions capable of detecting anomalous behavior indicative of exploitation attempts or post-exploitation activities. 6. Restrict user privileges to the minimum necessary, avoiding administrative rights for routine user accounts to limit the impact of successful exploitation. 7. Monitor network traffic and logs for unusual activity that may indicate exploitation attempts or lateral movement following compromise. 8. Regularly review and update patch management policies to ensure timely deployment of security updates across all endpoints.