CVE-2026-55021 Microsoft SharePoint Server Spoofing Vulnerability
An authorized attacker can perform spoofing via cross-site scripting in Microsoft SharePoint Server, requiring a vendor patch.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-55021?
CVE-2026-55021 is a high-severity cross-site scripting vulnerability in Microsoft Sharepoint Server, published on 14 Jul 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Office SharePoint allows an authorized attacker to perform spoofing over a network.
Weakness: CWE-79
Which versions are affected by CVE-2026-55021?
It affects 1 product.
Products include Microsoft Sharepoint Server.
How do I fix CVE-2026-55021?
No fix has been published for CVE-2026-55021 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-55021 being exploited?
There is no known exploitation of CVE-2026-55021 in the wild and no public exploit code.
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-c9qw-72v3-rp2r.