🚨 CVE-2025-49706 – SharePoint Spoofing Vulnerability Under Active Exploitation

By Aditya Bhatt – VAPT Specialist | Red Teamer

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📌 TL;DR

Microsoft SharePoint is under active threat. CVE‑2025‑49706, a spoofing vulnerability in SharePoint Server, has evolved from medium-severity to real-world weaponization, with a variant (CVE‑2025‑53770) now actively exploited in the wild. If you're running on-prem SharePoint 2016, 2019, or Subscription Edition, patch immediately or risk full compromise.

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🧠 The Vulnerability

CVE‑2025‑49706 affects:

• SharePoint Server 2016
• SharePoint Server 2019
• SharePoint Server Subscription Edition <16.0.18526.20424

➤ Root Cause:

The issue lies in improper authentication handling (CWE‑287). Authenticated attackers can spoof network requests, leading to potential impersonation and elevation of privileges.

🔒 CVSS Score:

• 6.3 (Medium) – CVSS v3.1 Despite the moderate rating, its chaining potential makes it much more dangerous.

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🧪 PoC Simulation (Ethical Red Teaming Use Only)

🚫 Disclaimer: The steps below are strictly for educational and defensive security purposes. Any unauthorized use against production systems without consent is illegal and unethical.

🔧 Scenario: Authenticated SharePoint user abuses spoofed POST request to trigger system-level code execution via chained web shell drop.

🧾 Requirements:

• Authenticated low-priv SharePoint user
• Burp Suite / MITM proxy
• Access to /sites/<vuln-site>/_layouts/15/SignOut.aspx
• A target endpoint that mishandles spoofed headers

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🔥 Steps Overview:

1. Log in to SharePoint with any authenticated user (no admin required).

2. Intercept a legitimate request to a known vulnerable endpoint (SignOut.aspx, UserProfileService.asmx, etc.) using Burp.

3. Modify headers such as:

   X-UserToken: spoofedtoken
   X-Ms-Client-Request-Id: {malicious-guid}

4. Replay the request with an embedded payload (e.g., dropper command or hidden aspx page injection).

5. Use POST parameters to upload:

   <form action="/_layouts/15/upload.aspx" method="POST" enctype="multipart/form-data">
     <input type="file" name="webshell.aspx">
   </form>

6. Navigate to the dropped shell (spinstall0.aspx) and trigger system commands via query params.

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⚡ Outcome:

• Attacker now controls a reverse shell or persistence implant via authenticated spoofing without triggering standard authN/authZ rules.
• If chained with CVE-2025-53770: full RCE on the SharePoint host.

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⚔️ Real-World Attacks: The “ToolShell” Campaign

Microsoft and security researchers have reported that CVE‑2025‑49706 is being chained with other bugs in active campaigns labeled "ToolShell". This multi-phase attack:

• Leverages CVE‑2025‑49706 + CVE‑2025‑49704
• Drops web shells like spinstall0.aspx
• Steals SharePoint authentication tokens
• Hijacks NT AUTHORITY\SYSTEM via process injection
• Installs malware payloads like SuspSignoutReq.exe

📌 It’s a full compromise scenario.

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🧩 Detection & IOCs

If you're running Defender for Endpoint or Defender AV:

• Watch for alerts like:

  • Possible web shell installation
  • Suspicious IIS Worker Behavior
  • HijackSharePointServer

• Hunt for spinstall0.aspx in:

  • C:\inetpub\wwwroot\wss\VirtualDirectories\*

📁 Other indicators:

• Dropped binaries: SuspSignoutReq.exe, sharepoint_helper.dll
• Suspicious outbound C2: .onion or random DNS traffic from SharePoint box

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🛡️ Mitigation: What You MUST Do Now

✅ PATCH IMMEDIATELY

Install the July 2025 Patch Tuesday updates:

• SharePoint 2016 ➤ KB5002744
• SharePoint 2019 ➤ KB5002741

🔗 Microsoft Update Catalog

✅ ENABLE AMSI + Defender AV

For real-time protection:

Set-MpPreference -EnableScriptScanning $true
Set-MpPreference -DisableRealtimeMonitoring $false

✅ BLOCK EXTERNAL ACCESS TEMPORARILY

If patching is delayed, isolate the SharePoint server from the internet to prevent initial payload delivery.

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🧠 Pro Tip – Custom Threat Hunt Query (Defender):

DeviceFileEvents
| where FileName contains "spinstall0.aspx" or FolderPath contains "inetpub"
| where ActionType == "FileCreated"

Use this KQL in Microsoft 365 Defender Advanced Hunting to detect web shell drops.

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🔚 Final Words

This is not just a CVE with a 6.3 rating — it’s a genuine lateral movement enabler, already leveraged by sophisticated threat actors. If you’re running an on-prem SharePoint instance and haven’t patched since June 2025 — you’re already a target.

🛡️ Patch fast. Monitor logs. Hunt threats. Stay safe.

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📚 References

• CVE-2025-49706 – NVD
• Microsoft Customer Guidance for CVE-2025-53770
• The Hacker News Coverage
• Wiz Threat Report

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👨‍💻 About the Author

I'm a cybersecurity practitioner with a strong focus on red teaming, vulnerability assessment, and offensive security. I’ve ranked in the top 2% on TryHackMe and built tools like KeySentry, PixelPhantomX, and ShadowHash that focus on key leakage detection, AI model evasion, and cryptographic operations.

I hold multiple certifications including CEH, CompTIA Security+, the Red Team Certificate from IIT Kanpur among others. I actively write for InfoSec WriteUps, where I share technical content for the security community, and I’ve contributed to Scopus-indexed research in cybersecurity and AI. I also regularly take part in hackathons and hands-on security challenges.

🔗 GitHub: @AdityaBhatt3010
✍️ Medium: @adityabhatt3010
💼 LinkedIn: Aditya Bhatt

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