CVE-2025-53770 Microsoft SharePoint Deserialization of Untrusted Data Vulnerability
Microsoft SharePoint Server on-premises contains a deserialization of untrusted data vulnerability that could allow an unauthorized attacker to execute code over a network. This vulnerability could be chained with CVE-2025-53771. CVE-2025-53770 is a patch bypass for CVE-2025-49704, and the updates for CVE-2025-53770 include more robust protection than those for CVE-2025-49704.
From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.
Should You Worry?
- CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 20 Jul 2025.
- CISA lists it as known to be used in ransomware campaigns.
- Rated Critical severity (CVSS 9.8, scored by Vendor).
- This product type is often exposed to the internet, which is where attackers scan for it first.
- It has been in the catalogue for 474 days. Systems still unpatched now have almost certainly been scanned for it.
What It Is
Deserialization of untrusted data in on-premises Microsoft SharePoint Server allows an unauthorized attacker to execute code over a network. Microsoft is aware that an exploit for CVE-2025-53770 exists in the wild. Microsoft is preparing and fully testing a comprehensive update to address this vulnerability. In the meantime, please make sure that the mitigation provided in this CVE documentation is in place so that you are protected from exploitation.
Affected Versions
| Product | Versions |
|---|---|
| Microsoft Microsoft SharePoint Enterprise Server 2016 | 16.0.0 to before 16.0.5513.1001 |
| Microsoft Microsoft SharePoint Server 2019 | 16.0.0 to before 16.0.10417.20037 |
| Microsoft Microsoft SharePoint Server Subscription Edition | 16.0.0 to before 16.0.18526.20508 |
From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.
What To Do Now
- 1
Find it
Search your asset inventory and external attack surface for Microsoft SharePoint. Include cloud images, appliances and anything a supplier runs for you.
Attack Surface Management - 2
Fix it
Disconnect public-facing versions of SharePoint Server that have reached their end-of-life (EOL) or end-of-service (EOS) to include SharePoint Server 2013 and earlier versions. For supported versions, please follow the mitigations according to CISA (URL listed below in Notes) and vendor instructions (URL listed below in Notes). Adhere to the applicable BOD 22-01 guidance for cloud services or discontinue use of the product if mitigations are not available.
Vulnerability Management - 3
Hunt for compromise
If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.
Incident Response - 4
Prove it is fixed
Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.
Penetration Testing
The Compliance Clock
General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.
Not Sure If You Are Exposed?
Our attack surface and vulnerability teams can check your internet-facing estate for CVE-2025-53770 and every other exploited flaw on the list.