Patch SharePoint Vulnerability CVE-2026-45659 Before It’s Too Late

A high-risk vulnerability in Microsoft SharePoint Server is being actively exploited, and SMBs must act quickly to protect their data.

The short version

CVE-2026-45659 is a high-risk SharePoint Server vulnerability being actively exploited.
Apply the Microsoft patch as soon as possible to protect your systems.
Review access logs for signs of unauthorized access or suspicious activity.
Contact a cybersecurity expert to verify your exposure and remediation steps.

What is CVE-2026-45659 and why is it dangerous?

CVE-2026-45659 is a vulnerability in Microsoft SharePoint Server that allows attackers to run arbitrary code on the server by exploiting how it processes untrusted data. In simple terms, if an attacker sends specially crafted data to your SharePoint Server, they could take control of it. This is dangerous because SharePoint is often used to store and share sensitive business information, making it a target for cybercriminals.

This vulnerability has been added to CISA’s Known Exploited Vulnerabilities (KEV) catalog as of July 1, 2026, which means it is already being actively exploited in the wild. That means attackers are already using this flaw to compromise systems. If your business uses SharePoint Server and hasn’t applied the patch, you are at risk of a breach.

How does this affect small and mid-sized businesses?

If your SMB uses Microsoft SharePoint Server, you are at risk from CVE-2026-45659. SharePoint is commonly used for document management, collaboration, and internal communications. If an attacker gains control of your SharePoint server, they could steal sensitive data, install malware, or even hold your systems for ransom. This could lead to operational downtime, financial loss, and reputational damage.

Even if your SharePoint instance is not exposed to the internet, internal attackers or compromised user accounts can still exploit the vulnerability. That’s why it’s critical to apply the patch as soon as possible. While the federal government has a July 4, 2026, deadline to remediate, SMBs should act quickly to reduce their risk of being targeted.

What should you do this week to protect your business?

First, confirm whether your organization is using Microsoft SharePoint Server. If so, apply the patch immediately. Microsoft has released a security update to address this vulnerability. Check the Microsoft Security Response Center for the specific patch KB number and instructions to apply it.

If you're not confident in your ability to apply the patch or verify its effectiveness, contact a cybersecurity expert to help. Delaying the patch could leave your business open to an attack. In addition to patching, review your SharePoint access logs for any unusual activity. Look for unexpected login attempts or file access patterns that could indicate a breach.

How can you tell if your business was already hit?

If you’re using SharePoint Server and haven’t applied the patch, there’s a chance your system has already been compromised. Look for signs such as unauthorized changes to files, unexpected system reboots, or unusual network traffic. Attackers may also install backdoors or other malicious tools that allow them to maintain access to your systems.

To detect a potential breach, review your SharePoint server logs for any suspicious activity. Look for failed login attempts, access from unfamiliar IP addresses, or any unauthorized changes to user permissions. If you find anything unusual, isolate the affected system and contact a cybersecurity professional for a full investigation.

Not sure whether your environment is exposed? That is exactly what our Vulnerability Management service is built to surface. Talk to us.

Frequently asked questions

Is this vulnerability being used by ransomware groups?

At this time, there is no confirmed evidence that CVE-2026-45659 is being used by ransomware groups. However, because the vulnerability is already being exploited in the wild, it could be used as part of a larger attack that leads to ransomware deployment. It’s important to patch now to prevent any potential follow-up attacks.

Do I need to patch if SharePoint is only used internally?

Yes. Even if your SharePoint instance is not exposed to the public internet, internal attackers or compromised user accounts can still exploit the vulnerability. Internal systems are not immune to cyberattacks, especially if user credentials are stolen or access is improperly configured.

What if I don’t use SharePoint Server?

If your business does not use Microsoft SharePoint Server, you are not directly affected by this vulnerability. However, it’s still worth verifying your software inventory to ensure no other systems are unknowingly at risk. Regularly reviewing your software and patching schedule is a best practice for all SMBs.

How can I confirm if the patch is applied correctly?

After applying the patch, review your SharePoint server logs and verify that the patch is listed in the installed updates. You can also use a vulnerability scanning tool to confirm that the system is no longer vulnerable to CVE-2026-45659. If you’re unsure, contact a cybersecurity expert to validate the patch status.

Source (public domain): CISA