CVE-2026-45659: Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability

What to do

1. Check whether your estate includes Microsoft SharePoint Server, including internet-facing devices.
2. Apply the vendor’s patch or mitigations (references below). Failing that, isolate the product or stop using it, as CISA requires of US federal agencies.
3. An exploited vulnerability has often been used before it was fixed: look for signs of compromise, especially on internet-facing devices.

References

• Vendor advisory or reference cited by CISA (msrc.microsoft.com)
• NVD entry (NIST)
• CISA KEV catalog