CVE-2026-20958 is a Server-Side Request Forgery (SSRF) vulnerability classified under CWE-918, affecting Microsoft SharePoint Enterprise Server 2016 version 16.0.0. SSRF vulnerabilities occur when an attacker can manipulate a server to send crafted requests to internal or external systems, potentially bypassing firewall restrictions and accessing sensitive information. In this case, the vulnerability allows an authorized attacker—meaning one with valid credentials—to induce the SharePoint server to make unauthorized network requests. This can lead to information disclosure over the network, impacting confidentiality and integrity of data. The vulnerability does not require user interaction and has a CVSS v3.1 base score of 5.4, indicating medium severity. The attack vector is network-based with low attack complexity and privileges required are low but authenticated. No known public exploits exist yet, and no patches have been linked at the time of publication, though Microsoft is expected to release updates. The vulnerability's scope is limited to the affected SharePoint version, but given SharePoint's widespread use in enterprise environments, the risk of internal network reconnaissance and data leakage is significant. The vulnerability does not impact availability, so denial of service is not a concern here. The SSRF can be leveraged to access internal services that are otherwise inaccessible externally, potentially enabling further attacks or data exfiltration.

For European organizations, this vulnerability poses a risk of unauthorized internal network reconnaissance and sensitive information disclosure via SharePoint servers. Many enterprises and public sector organizations across Europe rely on Microsoft SharePoint for collaboration and document management, making them potential targets. Exploitation could allow attackers to bypass perimeter defenses and access internal services, increasing the risk of lateral movement and data breaches. The confidentiality and integrity of sensitive corporate or governmental data could be compromised, especially if internal APIs or services are exposed through SSRF. Although availability is not impacted, the breach of sensitive information could lead to regulatory penalties under GDPR and damage to organizational reputation. The requirement for authenticated access limits the threat to insiders or attackers who have compromised credentials, but phishing or credential theft attacks are common, increasing the likelihood of exploitation. Organizations with complex internal networks and critical infrastructure integrated with SharePoint are at higher risk. The absence of known exploits currently provides a window for proactive mitigation.

Organizations should prioritize the following mitigations: 1) Apply official Microsoft patches immediately once available to remediate the vulnerability. 2) Restrict network access from SharePoint servers to only necessary internal services using network segmentation and firewall rules to limit SSRF impact. 3) Implement strict authentication and authorization controls to reduce the risk of credential compromise and unauthorized access. 4) Monitor SharePoint server logs and network traffic for unusual outbound requests indicative of SSRF exploitation attempts. 5) Employ Web Application Firewalls (WAFs) with SSRF detection capabilities to block malicious requests. 6) Conduct regular security audits and penetration testing focused on SSRF and related vulnerabilities. 7) Educate users on phishing and credential security to prevent initial access by attackers. 8) Consider disabling or restricting features in SharePoint that allow server-side HTTP requests if not required. These measures go beyond generic advice by focusing on network-level controls, monitoring, and user access management tailored to the SSRF threat vector.