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cve

CVE-2025-64672: SharePoint XSS Spoofing Flaw

Security Substrate

— 6 min read

CVE ID: CVE-2025-64672

Severity: HIGH | CVSS: 8.8

Sources: 2 different security sources

Let Me Explain What Happened

Well, my friends, Microsoft has disclosed a significant security vulnerability in SharePoint Server that we need to talk about. This one, tracked as CVE-2025-64672, is a cross-site scripting (XSS) vulnerability that allows an authenticated attacker to spoof content and potentially trick users into believing they're seeing legitimate SharePoint content when they're actually viewing something malicious. Think of it like someone being able to forge official-looking notices on your company bulletin board—except this bulletin board is your SharePoint server, and the consequences can be much more serious.

This vulnerability was disclosed as part of Microsoft's December 2025 Patch Tuesday release, which as the Zero Day Initiative noted, caps off the final security update cycle of the year. With a CVSS score of 8.8, this is classified as HIGH severity, and it deserves your immediate attention if you're running SharePoint in your environment.

A Bit More Detail

Here's what's going on under the hood: SharePoint Server isn't properly sanitizing user input before displaying it back in web pages. This is what we call "improper neutralization of input during web page generation"—a fancy way of saying that SharePoint is trusting data it shouldn't trust. When an authenticated user (someone who has legitimate login credentials) submits specially crafted input, SharePoint will render that input as active content in another user's browser session. This allows the attacker to inject malicious scripts that execute in the context of the SharePoint site, making it appear as though the content is legitimate.

What makes this particularly concerning is the spoofing aspect. An attacker could craft convincing fake login forms, fake security warnings, or fake administrative notices that appear to come from your SharePoint environment. Users who trust these spoofed elements might enter credentials, click malicious links, or take actions they wouldn't normally take if they knew the content wasn't genuine.

The Technical Specifics

  • Attack Vector: Network (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
  • Attack Complexity: Low—this doesn't require sophisticated techniques to exploit
  • Privileges Required: Low—the attacker needs to be authenticated, but doesn't need administrative privileges
  • User Interaction: None required for the initial exploit (though victims would need to view the spoofed content)
  • Scope: Unchanged—the vulnerability affects only the SharePoint application itself
  • Impact: High across all three CIA triad elements (Confidentiality, Integrity, and Availability)
  • Affected Products: Microsoft Office SharePoint Server (specific versions detailed in Microsoft's security guidance)
  • CWE Classification: CWE-79 (Improper Neutralization of Input During Web Page Generation, commonly known as Cross-Site Scripting)
  • First Disclosed: December 9, 2025, via Microsoft Security Response Center

Understanding the Attack Chain

Let me walk you through how an attacker might exploit this vulnerability, so you can better understand what you're defending against:

  • Step 1 - Initial Access: The attacker needs valid credentials to your SharePoint environment. This could be a malicious insider, a compromised account, or even a low-privilege service account.
  • Step 2 - Payload Crafting: The attacker creates a specially crafted input containing JavaScript or other client-side code. Because SharePoint doesn't properly sanitize this input, it will be stored and later rendered as active content.
  • Step 3 - Payload Delivery: The malicious content is injected into a SharePoint page, list item, web part, or other component that other users will view.
  • Step 4 - Victim Interaction: When legitimate users navigate to the affected SharePoint page, their browsers execute the malicious script in the context of the SharePoint site.
  • Step 5 - Exploitation: The attacker's script can now perform actions on behalf of the victim, steal session tokens, redirect to phishing sites, or display convincing spoofed content to harvest credentials.

Why This Matters More Than You Might Think

Now, you might be thinking, "It's just XSS—we see those all the time." And you're right that XSS vulnerabilities are common. But let me explain why this particular one deserves your attention. SharePoint is often the central collaboration hub for organizations, containing sensitive documents, project information, and serving as a trusted platform for internal communications. When users see content on SharePoint, they inherently trust it because it's coming from an internal, authenticated system.

This trust is exactly what makes spoofing so dangerous here. An attacker could create fake IT security announcements asking users to "verify their credentials," fake HR notices directing employees to malicious sites, or fake executive communications that could be used for business email compromise schemes. The high CVSS score of 8.8 reflects this reality—the combination of low attack complexity, network-based exploitation, and high impact across confidentiality, integrity, and availability makes this a serious threat.

What You Should Do About This

Let me guide you through the steps you need to take, starting with immediate actions and then moving to longer-term protective measures:

  • Right Now (Emergency Response):
    • Identify Your Exposure: Inventory all SharePoint Server instances in your environment. Check which versions you're running and whether they're affected by this vulnerability. Microsoft's security guidance at the MSRC portal will list specific affected versions.
    • Review Recent Activity: Examine SharePoint logs for unusual content creation or modification, especially in areas accessible to multiple users like shared lists, pages, and web parts. Look for JavaScript or HTML tags in content that shouldn't contain them.
    • Monitor User Reports: Brief your help desk team about this vulnerability and ask them to escalate any reports of unusual SharePoint behavior, unexpected pop-ups, or suspicious-looking content.
    • Consider Temporary Mitigations: If you cannot immediately patch, consider restricting SharePoint access to only essential users or implementing additional monitoring on SharePoint authentication and content modification.
  • For the Long Term (Remediation and Hardening):
    • Apply Microsoft's Security Updates: Visit the Microsoft Security Response Center guidance at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-64672 and download the appropriate patches for your SharePoint versions. Test these updates in a non-production environment first, then deploy to production following your change management procedures.
    • Implement Content Security Policy: Configure Content Security Policy (CSP) headers on your SharePoint sites to provide defense-in-depth against XSS attacks. This won't fix the vulnerability, but it adds an additional layer of protection.
    • Review SharePoint Permissions: Follow the principle of least privilege. Audit who has content creation and modification permissions in SharePoint. The fewer authenticated users who can create content, the smaller your attack surface.
    • Enable Enhanced Logging: Ensure you're capturing detailed SharePoint audit logs and forwarding them to your SIEM or log management platform. You want visibility into content changes for both detection and forensic purposes.
    • User Awareness: Brief your users about the possibility of spoofed content in SharePoint. Encourage them to verify unusual requests through secondary channels (like phone calls) rather than clicking links in unexpected SharePoint announcements.

Detection and Hunting Guidance

For those of you with security operations capabilities, here are some ways to hunt for potential exploitation attempts:

Log Analysis: Review SharePoint ULS logs and IIS logs for patterns indicating XSS attempts. Look for URL-encoded or HTML-encoded script tags in POST requests to SharePoint pages. Pay particular attention to requests containing strings like <script>, javascript:, onerror=, or onload= in unexpected fields.

Content Inspection: If you have the capability, scan SharePoint content databases or use SharePoint's search API to look for stored content containing script tags or JavaScript event handlers in fields that should only contain plain text or basic formatting.

Behavioral Monitoring: Watch for authenticated users who suddenly begin creating or modifying large amounts of content, especially if that content is being viewed by many other users. This could indicate an attacker using a compromised account to distribute malicious payloads.

Going Deeper: MITRE ATT&CK Context

For those of you who map threats to the MITRE ATT&CK framework, this vulnerability aligns with several techniques:

  • T1189 - Drive-by Compromise: While not a traditional drive-by, the stored XSS nature means users are compromised simply by viewing SharePoint content.
  • T1566 - Phishing: The spoofing capability enables sophisticated phishing attacks that appear to originate from trusted internal systems.
  • T1056 - Input Capture: Attackers could use injected scripts to capture keystrokes or form data entered on SharePoint pages.
  • T1539 - Steal Web Session Cookie: XSS is a classic technique for stealing session tokens and cookies to hijack authenticated sessions.

The Bigger Picture

This vulnerability was disclosed as part of Microsoft's December 2025 Patch Tuesday, which the Zero Day Initiative characterized as an exciting end to the year's security updates. While we only have limited details from the two sources reporting on this specific CVE, the timing and severity suggest Microsoft is taking this seriously as part of their year-end security housekeeping.

Cross-site scripting vulnerabilities in enterprise collaboration platforms like SharePoint represent a particularly insidious threat because they abuse the trust users place in internal systems. Unlike external phishing attacks that users are trained to be suspicious of, attacks leveraging SharePoint's trusted status can bypass many of our psychological defenses.

Final Thoughts

I know security patches can feel like an endless treadmill, especially during the busy holiday season when this was released. But this one is worth prioritizing. The combination of high severity, low attack complexity, and the central role SharePoint plays in many organizations makes CVE-2025-64672 a vulnerability that attackers will likely attempt to exploit.

Take the time to patch your SharePoint servers, review your permissions, and ensure your monitoring is in place. Your future self—and your users—will thank you for it.

Stay safe out there, and remember: security is a journey, not a destination. Each patch applied, each log reviewed, and each user educated makes your environment that much more resilient.

Where I Found This Information

Note: This is automated security intelligence based on multiple sources. Always test updates carefully in a non-production environment before applying them to production systems. Consult Microsoft's official security guidance for complete patch deployment instructions specific to your SharePoint version.

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