Microsoft SharePoint Deserialization Vulnerability Actively Exploited

Microsoft SharePoint contains a deserialization of untrusted data vulnerability that allows an unauthorized attacker to execute code over a network, with CVE-2026-58644 actively being exploited as of July 19, 2026.

Understanding the Vulnerability

The deserialization of untrusted data vulnerability in Microsoft SharePoint, CVE-2026-58644, is a critical issue that can be exploited by attackers to execute arbitrary code on affected systems. This is particularly concerning given the widespread use of SharePoint in enterprise environments for collaboration and document management.

Attack Vector

An attacker could exploit this vulnerability by sending specially crafted requests to a vulnerable SharePoint server, potentially leading to code execution and further malicious activities such as data theft, lateral movement within the network, or deployment of additional malware.

Who Is Affected

Organizations using Microsoft SharePoint are potentially at risk, particularly those with internet-exposed SharePoint servers. The vulnerability affects Microsoft SharePoint, and all versions are considered vulnerable until the appropriate patches are applied.

What the Sceptics Say

Some might argue that since a patch is available, the risk is mitigated for those who keep their systems up to date. However, the reality is that not all organizations may have applied the latest security updates due to various reasons such as compatibility issues, lack of resources, or simply because they are not aware of the vulnerability.

How to Defend

• Apply the latest security patches for Microsoft SharePoint as soon as possible to mitigate the vulnerability.
• Monitor network traffic for signs of exploitation attempts or suspicious activity.
• Implement additional security measures such as intrusion detection systems and firewalls to limit exposure.

Key Takeaways

1. Security Teams: Prioritize patching Microsoft SharePoint servers and monitor for signs of exploitation.
2. CISOs: Ensure that vulnerability management processes are in place and being followed to address known vulnerabilities promptly.
3. Developers: Be aware of secure coding practices, especially concerning deserialization of data, to prevent similar vulnerabilities in custom applications.
4. End Users: Be cautious of phishing attempts that might be used as a precursor to exploiting vulnerabilities like CVE-2026-58644.

Sources

• NIST: CVE-2026-58644
• NIST: CVE-2026-25089
• NIST: CVE-2026-39808