CVE-2023-29357 is a critical security vulnerability identified in Microsoft SharePoint Server 2019 (version 16.0.0), classified under CWE-303, which pertains to incorrect implementation of authentication algorithms. This flaw enables an unauthenticated remote attacker to elevate privileges on the affected system without requiring any user interaction. The vulnerability arises from improper handling of authentication processes within SharePoint Server, allowing attackers to bypass normal access controls and gain elevated permissions. With a CVSS v3.1 base score of 9.8, the vulnerability is rated critical due to its network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), and no user interaction needed (UI:N). The impact metrics indicate high confidentiality (C:H), integrity (I:H), and availability (A:H) impacts, meaning an attacker can fully compromise the system, access sensitive data, modify content, and disrupt services. Although no public exploits have been reported yet, the vulnerability's characteristics make it a prime candidate for exploitation once weaponized. SharePoint Server is widely used in enterprise environments for collaboration and document management, making this vulnerability particularly dangerous in business-critical contexts. The lack of available patches at the time of reporting increases the urgency for organizations to implement interim mitigations and monitor for suspicious activity.

For European organizations, the impact of CVE-2023-29357 is significant due to the widespread use of Microsoft SharePoint Server 2019 in government, finance, healthcare, and industrial sectors. Successful exploitation could lead to unauthorized access to confidential documents, intellectual property theft, data manipulation, and disruption of collaborative workflows. This could result in regulatory non-compliance, financial losses, reputational damage, and operational downtime. Given the critical nature of the vulnerability, attackers could leverage it to establish persistent footholds within networks, facilitating further lateral movement and advanced persistent threats (APTs). The vulnerability poses a heightened risk to organizations with externally accessible SharePoint servers or those lacking robust network segmentation. The potential for full system compromise elevates the threat to national critical infrastructure and large enterprises, making it a priority for cybersecurity defenses in Europe.

To mitigate CVE-2023-29357, European organizations should immediately assess their SharePoint Server 2019 deployments and restrict external network access to these servers using firewalls and network segmentation. Implement strict access controls and monitor authentication logs for unusual privilege escalation attempts. Employ application-layer gateways or web application firewalls (WAFs) to detect and block suspicious requests targeting SharePoint authentication mechanisms. Until an official patch is released, consider disabling or limiting features that expose authentication endpoints externally. Conduct thorough vulnerability scanning and penetration testing focused on SharePoint environments. Maintain up-to-date backups and develop incident response plans specific to SharePoint compromise scenarios. Engage with Microsoft security advisories regularly to apply patches promptly once available. Additionally, educate IT staff on the risks of this vulnerability and ensure multi-factor authentication is enforced for administrative access where possible.