Type Vulnerability
Microsoft SharePoint contains a deserialisation of untrusted data vulnerability that allows an unauthorised attacker to execute code over a network. Known-exploited catalogue reports exploitation in the wild.
Microsoft · Parser conflict
Microsoft SharePoint Unsafe Deserialisation Vulnerability
CVE-2026-20963
What this means
This is rated critical severity (9.8 out of 10). It is on the known-exploited catalogue, which means attacks using it have already been seen. Ask IT whether Microsoft Sharepoint Server is in your estate, and treat that as the priority.
Full vendor description
Deserialization of untrusted data in Microsoft Office SharePoint allows an unauthorized attacker to execute code over a network.
Scoring and exploitation
9.8/ 10
CVSS 3.1 base scoreCritical
Exploitable over the network without any account, and no one has to click or open anything. High impact on confidentiality, integrity and availability.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Exploitability
Longer bar: easier to attack
Attack vectorNetworkAV:N
Attack complexityLowAC:L
Privileges requiredNonePR:N
User interactionNoneUI:N
ScopeUnchangedS:U
Impact
Longer bar: more harm
ConfidentialityHighC:H
IntegrityHighI:H
AvailabilityHighA:H
- Elevated attack likelihood (~29.2% in 30 days)Model estimate (): a probability signal, not confirmed exploitation
- Exploited in the wild
- Yes — confirmed exploitation (US CISA )
- Not reported
- Listed product
- Microsoft SharePoint
Weaknesses
CWE-502
Affected products ()
- Microsoft Sharepoint Server
Show the raw CPE strings (3)
- cpe:2.3:a:microsoft:sharepoint_server:*:*:*:*:subscription:*:*:*
- cpe:2.3:a:microsoft:sharepoint_server:2016:*:*:*:enterprise:*:*:*
- cpe:2.3:a:microsoft:sharepoint_server:2019:*:*:*:*:*:*:*
References
2 links from the CVE record, grouped by site; the vendor's advisory comes first.
msrc.microsoft.com1 linkVendor advisory
- CVE-2026-20963 (opens in a new tab)Vendor Advisory
cisa.gov1 link
- known-exploited-vulnerabilities-catalog (opens in a new tab)US Government Resource