SharePoint Servers Exploited via Zero-Day Vulnerability (CVE-2025-53770): No Patch Available
Critical SharePoint Zero-Day Flaw (CVE-2025-53770) Under Active Attack: How to Protect Your Servers
A severe, unpatched zero-day vulnerability in Microsoft SharePoint Server, tracked as CVE-2025-53770, is being actively exploited in the wild. This critical security flaw allows attackers to achieve remote code execution (RCE) on affected servers, posing a significant threat to organizations relying on on-premises SharePoint deployments.
At this time, no official patch has been released by Microsoft, leaving many systems vulnerable. Security teams and administrators must take immediate action to mitigate the risk and defend against potential compromise.
Understanding the Threat: What is CVE-2025-53770?
CVE-2025-53770 is a high-severity vulnerability that affects on-premises Microsoft SharePoint Server instances. The flaw allows an unauthenticated attacker to send a specially crafted request to a vulnerable SharePoint server and execute arbitrary code.
This type of attack is particularly dangerous for several reasons:
- It is a zero-day vulnerability, meaning it was discovered and exploited by malicious actors before a security patch was available.
- It allows for remote code execution (RCE), which is one of the most critical types of vulnerabilities. A successful exploit gives an attacker deep control over the server.
- Active exploitation is confirmed, indicating that cybercriminals are already using this flaw to target organizations.
This vulnerability primarily impacts self-hosted, on-premises SharePoint environments. Organizations using SharePoint Online are generally not affected, as the cloud infrastructure is managed and secured by Microsoft.
The Potential Impact of an Exploit
If an attacker successfully exploits CVE-2025-53770, they could achieve a complete server takeover. This access could be used to:
- Steal, modify, or delete sensitive corporate data stored on the SharePoint server.
- Deploy ransomware to encrypt files and disrupt business operations.
- Establish a persistent foothold within the corporate network to move laterally and compromise other systems.
- Use the compromised server as a launchpad for further attacks against internal or external targets.
The consequences of a successful breach can range from significant data loss and financial damage to severe reputational harm.
Urgent Security Measures: How to Mitigate Risk Without a Patch
With no official patch available, proactive mitigation is the only defense. Administrators responsible for on-premises SharePoint servers should implement the following measures immediately.
1. Restrict Untrusted Network Access
If your SharePoint server must be accessible from the internet, strictly limit access to trusted IP addresses. If external access is not essential for business operations, consider taking the server offline or placing it behind a VPN until a patch is released. This is the single most effective way to prevent external exploitation.
2. Implement URL Rewrite Rules
A common temporary fix for web-based vulnerabilities is to use a URL rewrite module to block malicious patterns. Administrators can configure the Internet Information Services (IIS) web server that hosts SharePoint to create a rule that blocks requests containing suspicious patterns known to be associated with the exploit. This can serve as a virtual patch while waiting for an official update.
3. Enhance Monitoring and Logging
Increase the logging level on your SharePoint servers and actively monitor for Indicators of Compromise (IoCs). Look for:
- Unusual w3wp.exe process activity, such as unexpected child processes or high CPU usage.
- Suspicious network connections originating from the SharePoint server to unknown destinations.
- The appearance of unexpected files (e.g., .aspx, .php) in web-accessible directories, which could indicate a webshell has been planted.
4. Review Backup and Recovery Plans
Ensure you have recent, tested, and offline backups of your SharePoint data and server configurations. In a worst-case scenario, such as a ransomware attack, a reliable backup is critical for restoring operations quickly and without paying a ransom.
Stay Vigilant and Prepare for the Patch
This is a developing security situation. The vulnerability poses a clear and present danger to any organization running a vulnerable version of SharePoint Server. While the mitigation steps above can significantly reduce your attack surface, they are not a permanent solution.
It is crucial to monitor official channels for the release of a security patch and be prepared to apply it as soon as it becomes available. Proactive defense today is the best strategy to protect your organization’s critical assets from this ongoing threat.
Source: https://www.helpnetsecurity.com/2025/07/20/microsoft-sharepoint-servers-under-attack-via-zero-day-vulnerability-with-no-patch-cve-2025-53770/
