Critical SharePoint Zero-Day Under Active Attack: How to Protect Your Servers Now
A critical zero-day vulnerability in Microsoft SharePoint Server is being actively exploited by threat actors, allowing for remote code execution (RCE) on affected systems. This high-severity flaw enables authenticated attackers to gain administrative privileges, and security researchers warn that it is being chained with other vulnerabilities to achieve full server compromise.
The most alarming aspect of this developing situation is that no official patch is currently available, leaving countless organizations exposed to potential attacks. If your organization uses SharePoint Server, immediate action is required to mitigate this threat.
Understanding the SharePoint Vulnerability
The core of this exploit is a privilege escalation flaw. In simple terms, an attacker who already has some level of access to a SharePoint server can exploit this vulnerability to elevate their permissions to that of a high-level administrator. This is the first step in a more complex attack chain.
Security experts have observed threat actors combining this privilege escalation bug with a separate code injection vulnerability. This two-stage process works as follows:
- Privilege Escalation: The attacker uses the zero-day flaw to gain administrative rights on the SharePoint server.
- Remote Code Execution: With elevated privileges, the attacker then exploits a second known vulnerability to execute arbitrary code, effectively giving them full control over the compromised server.
Once an attacker achieves RCE, they can deploy malware, steal sensitive data, create backdoors for persistent access, or use the server as a pivot point to move deeper into your network.
The Threat: Unpatched and Actively Exploited
The term “zero-day” refers to a vulnerability that has been discovered by attackers before the software vendor has had a chance to develop and release a patch. This creates a critical window of opportunity for malicious actors.
In this case, proof-of-concept (PoC) exploit code has been publicly released, making it significantly easier for even less-skilled attackers to target vulnerable SharePoint instances. The combination of an unpatched flaw, active exploitation in the wild, and publicly available exploit code creates a perfect storm for cybersecurity defenders.
Actionable Mitigation Steps: What to Do Now
Since there is no security patch to apply, organizations must focus on mitigation and detection. Taking proactive steps is the only way to defend against these ongoing attacks.
Here are the essential security measures your IT and security teams should implement immediately:
- Restrict Access: If possible, limit access to your SharePoint server from the internet. If it must be public-facing, enforce strict access controls and consider allowing connections only from trusted IP address ranges.
- Disable the ‘Public’ Anonymous Access Feature: Microsoft has issued guidance recommending that administrators disable anonymous access sharing features for SharePoint lists and libraries. This may help disrupt the initial stages of an attack.
- Monitor for Indicators of Compromise (IoCs): Scrutinize your SharePoint server logs for any unusual activity. Look for suspicious PowerShell commands, unexpected file creation in SharePoint directories, or processes being spawned by the SharePoint service account that are out of the ordinary. Constant monitoring is key to early detection.
- Apply a ‘Defense-in-Depth’ Strategy: Ensure that other security layers are in place. Your endpoint detection and response (EDR) solution, firewall rules, and network segmentation can help contain an attack even if the initial server is breached.
- Prepare for Patch Deployment: While no patch exists today, one will eventually be released. Ensure your team is prepared to test and deploy it as soon as it becomes available. Sign up for security notifications from Microsoft to stay informed.
This situation serves as a stark reminder of the importance of a robust security posture. While waiting for an official fix, proactive monitoring, access control, and a layered defense strategy are your best defenses against this critical SharePoint vulnerability.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-sharepoint-zero-day-exploited-in-rce-attacks-no-patch-available/
