Summary
CVE-2025-49706 is an improper authentication vulnerability in Microsoft SharePoint, disclosed at Pwn2Own Berlin 2025. It affects the ToolPane endpoint, where SharePoint mistakenly trusts crafted Referer headers. Attackers can send one fake HTTP request with a spoofed Referer to access protected SharePoint APIs without logging in, enabling impersonation and abuse. This flaw, part of the ToolShell chain, is often combined with CVE-2025-49704 for remote code execution. Microsoft fixed it on July 8, 2025.
Urgent Actions Required
- Apply Microsoft’s July 8, 2025 security update for SharePoint Server 2016, 2019, and Subscription Edition.[2] [3]
- Block unauthenticated access to the /ToolPane.aspx endpoint via Web Application Firewall (WAF) or reverse proxy.
- Monitor network traffic for suspicious requests with spoofed Referer headers pointing to /layouts/SignOut.aspx.
- Check for signs of compromise including access to /spinstall0.aspx and usage of malicious ASPX payloads.
- Regenerate cryptographic machine keys if unauthorized access is suspected.
Which Systems Are Vulnerable to CVE-2025-49706?
Technical Overview
- Vulnerability Type: Improper Authentication via Referer Header Spoofing
- Affected Software/Versions:
- Microsoft SharePoint Server 2016
- Microsoft SharePoint Server 2019
- Microsoft SharePoint Server Subscription Edition (On-Prem)
- Attack Vector: Network (HTTP)
- CVSS Score: 6.5
- Exploitability Score:
- Attack Vector: Network
- Attack Complexity: Low
- Privileges Required: None
- User Interaction: None
- Patch Availability: Yes, released July 8, 2025[1]
How Does the CVE-2025-49706 Exploit Work?
The attack typically follows these steps:
What Causes CVE-2025-49706?
Vulnerability Root Cause:
This vulnerability arises from improper authentication handling in Microsoft SharePoint’s ToolPane endpoint. SharePoint fails to validate the Referer HTTP header correctly and mistakenly trusts spoofed values. By crafting a request with a Referer pointing to /layouts/SignOut.aspx, attackers can trick SharePoint into treating the request as authenticated. This flaw enables unauthenticated access to protected APIs, allowing attackers to impersonate users and abuse SharePoint functionality without credentials or user interaction.
How Can You Mitigate CVE-2025-49706?
If immediate patching is delayed or not possible:
- Block or filter malicious requests targeting the /_layouts/15/ToolPane.aspx endpoint using a web application firewall (WAF).
- Monitor HTTP traffic for spoofed Referer headers, particularly those referencing /layouts/SignOut.aspx.
- Inspect logs for unusual ToolPane access patterns that may indicate exploitation attempts.
- Implement strong authentication mechanisms across all SharePoint endpoints to reduce exposure.
- Harden access controls and review permissions for sensitive SharePoint features to prevent abuse.
Which Assets and Systems Are at Risk?
Asset Types Affected:
- Microsoft SharePoint OnPremise Servers – including SharePoint Server Subscription Edition, 2019, and 2016
- Web Interfaces and APIs – particularly those exposed via the vulnerable /ToolPane.aspx endpoint
- Public-Facing SharePoint Deployments – systems accessible over HTTP/S that evaluate request headers for access decisions
Exposure Level:
- Internet-Facing SharePoint Servers – unpatched servers are being actively exploited in the wild, as confirmed by multiple security vendors
- Internally Hosted SharePoint Instances – still affected if accessible via internal networks and not yet patched
Will Patching CVE-2025-49706 Cause Downtime?
Patch application impact: Low downtime. Microsoft’s July 8, 2025 security update fixes CVE-2025-49706. Most SharePoint environments can apply the patch with minimal disruption. Test first if using custom configurations.
How Can You Detect CVE-2025-49706 Exploitation?
Exploitation Signatures:
Look for unauthenticated HTTP requests to the SharePoint ToolPane endpoint with a spoofed Referer header pointing to /layouts/SignOut.aspx.
Indicators of Compromise (IOCs/IOAs):
- Requests to ToolPane endpoint containing Referer: /layouts/SignOut.aspx
- Access to protected SharePoint APIs without credentials
Behavioral Indicators:
- SharePoint treats unauthenticated requests as trusted because of the spoofed Referer
- Unauthorized access to SharePoint features or APIs
Alerting Strategy:
- Priority: Medium
- Trigger alerts for:
- Requests with Referer set to /layouts/SignOut.aspx targeting ToolPane
- Access to protected APIs without authentication
Remediation & Response
Patch/Upgrade Instructions:
- Apply Microsoft’s security update released on July 8, 2025, to patch the vulnerability in SharePoint.[1]
Mitigation Steps if No Patch:
- Monitor and block suspicious HTTP requests with spoofed Referer headers targeting the ToolPane endpoint (e.g., requests referencing /layouts/SignOut.aspx).
- Use Web Application Firewall (WAF) or proxy rules to filter or block unauthenticated requests with abnormal Referer headers aimed at SharePoint APIs.
Remediation Timeline:
- Immediate (0–2 hrs): Implement monitoring and request filtering at the edge or proxy level.
- Within 24 hrs: Apply the official Microsoft patch to all affected SharePoint instances.
Rollback Plan:
- If the patch causes issues, revert to the last stable SharePoint version and maintain monitoring/filtering rules.
- Document rollback procedures clearly with version and timing details.
Incident Response Considerations:
- Quickly isolate affected SharePoint servers to prevent unauthorized access via crafted Referer headers.
- Collect logs from reverse proxies and SharePoint access logs to identify suspicious unauthenticated requests.
- Investigate potential unauthorized API access and user impersonation attempts.
- After patching, increase logging and validate that requests to protected APIs require proper authentication and valid headers.
Compliance & Governance Notes
Audit Trail Requirement:
- Log requests with spoofed Referer headers targeting the ToolPane endpoint, including timestamp, source IP, and URI.
- Record patch deployment details such as date and responsible personnel.
Policy Alignment:
- Update policies to validate Referer headers and prevent spoofing.
- Include specific response steps for this vulnerability in the Incident Response Plan.
Where Can I Find More Information on CVE-2025-49706?
- ^CVE-2025-49706 – Security Update Guide – Microsoft – Microsoft SharePoint Server Spoofing Vulnerability
- ^Description of the security update for SharePoint Enterprise Server 2016: July 8, 2025 (KB5002744) – Microsoft Support
- ^Description of the security update for SharePoint Server Subscription Edition: July 8, 2025 (KB5002751) – Microsoft Support
- ^Disrupting active exploitation of on-premises SharePoint vulnerabilities | Microsoft Security Blog
- ^NVD – CVE-2025-49706
CVSS Breakdown Table
| Metric | Value | Description |
|---|---|---|
| Base Score | 6.5 | Medium severity vulnerability with significant impact and exploitability |
| Attack Vector | Network | Exploitable remotely over HTTP without local access |
| Attack Complexity | Low | Exploit does not require special conditions; straightforward |
| Privileges Required | None | No authentication or elevated privileges needed to exploit |
| User Interaction | None | No user action required for exploitation |
| Scope | Unchanged | Exploitation affects only the vulnerable component |
| Confidentiality Impact | Low | Limited disclosure of sensitive data possible |
| Integrity Impact | Low | Limited unauthorized modification or bypass of controls |
| Availability Impact | None | No impact on system availability expected |
