CVE-2026-55040 Microsoft SharePoint Weak Authentication
An unauthorized attacker can bypass security features in Microsoft SharePoint Server via weak authentication mechanisms.
- Exploited in the wild
- Since 18 Aug 2026
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-55040?
CVE-2026-55040 is a critical vulnerability in Microsoft Sharepoint Server, published on 14 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Weakness: CWE-1390
Which versions are affected by CVE-2026-55040?
It affects 1 product.
Products include Microsoft Sharepoint Server.
How do I fix CVE-2026-55040?
No fix has been published for CVE-2026-55040 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 21 Aug 2026.
Is CVE-2026-55040 being exploited?
Yes. Attackers have exploited CVE-2026-55040 in the wild since at least 18 Aug 2026.
Public exploit code: 1 Nuclei template and 5 proofs of concept on GitHub.
Other vulnerabilities in Microsoft Sharepoint Server
- CVE-2026-50522 Microsoft SharePoint Deserialization of Untrusted Data Vulnerability
- CVE-2026-58644 Microsoft SharePoint Deserialization of Untrusted Data
- CVE-2026-20963 Microsoft SharePoint Deserialization of Untrusted Data
- CVE-2025-53770 Microsoft SharePoint Deserialization of Untrusted Data
- CVE-2023-29357 Microsoft SharePoint Server Privilege Escalation
Sources
Also known as GHSA-grxw-7cvc-96rv.