CVE-2026-45659: Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 1 Jul 2026, 40 days after the CVE record was published.
- How likely is exploitation in the next 30 days?
- 80.2%
EPSS score, percentile 99.6 of all scored records
- How severe?
- 8.8 High
CVSS v3.1 base score, given by the CNA
- What should I do?
CISA deadline 4 Jul 2026. Apply mitigations in accordance with vendor instructions … Full text
- Which versions are affected?
Affected
- from 16.0.0 to before 16.0.5552.1002
- from 16.0.0 to before 16.0.10417.20128
- from 16.0.0 to before 16.0.19725.20280
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
What to do
Required action, set by CISA
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
CISA due date for this action: 4 July 2026.
Advisories and patches
Linked from CISA's catalog entry
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45659
- https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
- https://nvd.nist.gov/vuln/detail/CVE-2026-45659
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | from 16.0.0 to before 16.0.5552.1002 |
| Status | Versions |
|---|---|
| Affected | from 16.0.0 to before 16.0.10417.20128 |
| Status | Versions |
|---|---|
| Affected | from 16.0.0 to before 16.0.19725.20280 |
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
About this vulnerability
Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network.
Summary: CISA's KEV catalog, as of 28 Oct 2026.
- CISA added CVE-2026-45659 to its Known Exploited Vulnerabilities (KEV) catalog on 1 Jul 2026.
- CISA marks it as known to be used in ransomware campaigns.
- The due date CISA sets for the required action is 4 Jul 2026.
- The CVE record was published on 22 May 2026, 40 days before it was added to KEV.
- The CVE record carries a CVSS v3.1 base score of 8.8 (High), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 80.2% (percentile 99.6), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact total.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.
Description
Microsoft SharePoint Remote Code Execution Vulnerability
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
Weakness
- CWE-502: Deserialization of Untrusted Data
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| 22 May 2026 | CVE record published |
| 1 Jul 2026 | Added to CISA KEV |
| 4 Jul 2026 | CISA due date for the required action |
| 11 Aug 2026 | CVE record last updated |
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