Microsoft SharePoint is a critical collaboration platform for many organizations, storing everything from internal documents and policies to financial information and employee resources.
That makes it an attractive target for cybercriminals.
Recent security activity involving on-premises Microsoft SharePoint Server is a reminder that businesses cannot afford to treat security updates as routine maintenance that can always wait until later.
SharePoint Vulnerabilities Are Being Actively Exploited
The Cybersecurity and Infrastructure Security Agency (CISA) recently added CVE-2026-55040, a Microsoft SharePoint weak-authentication vulnerability, to its Known Exploited Vulnerabilities (KEV) Catalog after evidence showed that attackers were actively exploiting it.
This follows additional SharePoint security issues disclosed earlier this summer.
In July, CISA warned that attackers were exploiting several SharePoint vulnerabilities affecting supported versions of on-premises SharePoint Server, including SharePoint Server 2016, SharePoint Server 2019, and SharePoint Server Subscription Edition.
Microsoft's July security release also identified SharePoint vulnerabilities where exploitation had been detected, including vulnerabilities capable of privilege escalation and remote code execution.
In other words, this isn't simply a theoretical security problem.
Attackers are actively looking for vulnerable SharePoint environments.
Why This Matters to Businesses
A vulnerable SharePoint server can potentially provide attackers with an entry point into a much larger business network.
Depending on the vulnerability and configuration, successful exploitation could potentially allow an attacker to:
- Gain unauthorized access to a SharePoint environment
- Execute malicious code on a server
- Access or steal business information
- Establish persistence within the environment
- Deploy additional malware
- Use the compromised server as a foothold for attacks against other systems
CISA previously warned that attackers exploiting SharePoint vulnerabilities were conducting post-exploitation activities such as stealing IIS machine keys and attempting to maintain persistent access.
For organizations storing sensitive operational information in SharePoint, the consequences can extend well beyond one compromised application.
“We Installed the Patch” May Not Be Enough
Installing Microsoft's security updates should be a priority, but organizations should also consider whether attackers may have accessed a vulnerable server before it was patched.
This is an important distinction.
Patching closes known vulnerabilities, but it doesn't automatically remove an attacker who already established another method of accessing the environment.
Businesses running affected SharePoint servers should therefore combine patching with a broader security review.
What Businesses Should Do Now
Organizations using on-premises Microsoft SharePoint Server should take several immediate steps.
1. Verify your SharePoint version and patch level
Confirm that supported Microsoft security updates have been installed across every SharePoint server—not just the primary server.
2. Determine whether SharePoint is exposed to the internet
Internet-facing infrastructure typically carries greater risk because attackers can continuously scan the internet looking for vulnerable systems.
Organizations should evaluate whether direct internet exposure is actually necessary.
3. Review the environment for suspicious activity
Administrators should review SharePoint, Windows, IIS, firewall, endpoint security, and authentication logs for unusual activity.
Pay particular attention to unexpected administrative activity, unusual processes, suspicious outbound connections, or authentication behavior that doesn't match normal business operations.
4. Review privileged accounts
Compromised administrator credentials can turn an application vulnerability into a much larger network compromise.
Organizations should review administrative accounts, remove unnecessary privileges, and ensure strong multifactor authentication is being used wherever possible.
5. Make sure endpoint detection is running on servers
Modern endpoint detection and response (EDR) platforms can provide another layer of visibility when suspicious processes or behaviors occur on critical servers.
6. Review your backup and recovery strategy
Cybersecurity isn't only about preventing attacks.
Businesses should maintain tested backups of critical information and understand how systems would be restored following ransomware, data corruption, or another major security incident.
Cybersecurity Requires More Than Installing Updates
The SharePoint situation highlights a larger cybersecurity lesson.
Businesses increasingly depend on interconnected systems including Microsoft 365, servers, firewalls, VPNs, cloud applications, endpoints, and remote-access services.
Attackers only need to find one weak point.
That's why effective cybersecurity requires multiple layers of protection—including vulnerability management, endpoint security, multifactor authentication, network monitoring, backups, email security, and ongoing security reviews.
Is Your Business Infrastructure Properly Protected?
At MicroAdvantage, we help businesses evaluate and strengthen their IT infrastructure before vulnerabilities turn into larger problems.
Our team can help review areas including:
- Microsoft 365 security
- Microsoft Defender and endpoint protection
- Server and workstation security
- Firewall and network configuration
- Multifactor authentication
- Patch and vulnerability management
- Backup and disaster recovery
- Email security
- Remote-access and VPN security
If you're unsure whether your systems are properly patched, protected, and monitored, MicroAdvantage can help review your environment and identify potential gaps before attackers find them first.