Threats / Microsoft / CVE-2026-20963
CVE-2026-20963
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
Microsoft SharePoint vulnerability
Microsoft SharePoint contains a deserialization of untrusted data vulnerability allowing remote code execution. The flaw has been exploited in the wild.
Verdict
Today item — known-exploited.
An unauthenticated attacker can exploit unsafe deserialization in SharePoint to execute arbitrary code remotely without authentication, posing immediate risk to affected deployments.
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
4 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2026-03-18).
Probability (EPSS)
EPSS 0.31109 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: Microsoft, SharePoint. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-502 Deserialization of Untrusted Data — weakness family: Injection.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious serialized object and send it to a vulnerable SharePoint endpoint.
Business
Attackers gain initial network access to enterprise collaboration infrastructure.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
The server deserializes my untrusted payload, triggering code execution during object reconstruction.
Business
Arbitrary code runs with SharePoint service account privileges, bypassing authentication controls.
3
Lateral reach — past segmentation narrative 3
Attacker
I establish persistence and move laterally across the network from the compromised SharePoint server.
Business
Breach scope expands from a single service to enterprise systems, documents, and user credentials.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05